Staff Publications

Staff Publications

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    'Staff publications' is the digital repository of Wageningen University & Research

    'Staff publications' contains references to publications authored by Wageningen University staff from 1976 onward.

    Publications authored by the staff of the Research Institutes are available from 1995 onwards.

    Full text documents are added when available. The database is updated daily and currently holds about 240,000 items, of which 72,000 in open access.

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Leaf phenolics and seaweed tannins : analysis, enzymatic oxidation and non-covalent protein binding
Vissers, Anne M. - \ 2017
University. Promotor(en): Harry Gruppen; Wouter Hendriks, co-promotor(en): Jean-Paul Vincken. - Wageningen : Wageningen University - ISBN 9789463432023 - 154
phenols - leaves - seaweeds - tannins - beta vulgaris - laminaria - proteins - catechol oxidase - nuclear magnetic resonance spectroscopy - in vitro - mass spectrometry - browning - fermentation - animal feeding - fenolen - bladeren - zeewieren - tanninen - eiwitten - kernmagnetische resonantiespectroscopie - massaspectrometrie - bruinkleuring - fermentatie - diervoedering

Upon extraction of proteins from sugar beet leaves (Beta vulgaris L.) and oarweed (Laminaria digitata) for animal food and feed purposes, endogenous phenolics and proteins can interact with each other, which might affect the protein’s applicability. Sugar beet leaf proteins might become covalently modified by phenolics through polyphenol oxidase (PPO) activity. Oligomeric phenolics from seaweed (so-called phlorotannins (PhT)) might bind non-covalently to protein. The first aim of this thesis was to study factors involved in protein modification by phenolics. The second aim was to investigate the effect of PhT supplementation to feed on in vitro ruminal fermentation.

Besides PPO activity and the amount of low molecular weight phenolic substrates present, brown colour formation in sugar beet leaves was dependent on the amount of phenolics, which do not serve as a substrate of PPO. These non-substrate phenolics can engage in browning reactions by oxidative coupling and subsequent coupled oxidation of the products formed. Similar reactions might also be involved in covalent protein modification by phenolics, and therewith protein properties.
High molecular weight PhT from L. digitata could potentially modify protein properties by non‑covalent interactions. L. digitata contained PhT with subunits mainly connected via C‑O-C linkages, as determined using NMR spectroscopy. Further mass spectrometric analysis revealed the presence of a wide range of oligomers with degrees of polymerisation between 3 and 27. The interaction between PhT and proteins (b-casein and bovine serum albumin) was studied using model systems with different pH values, representing the various environments throughout the ruminants digestive tract. Phlorotannins bound to protein independent of pH, and broadened the pH range of protein precipitation from 0.5 to ~1.5 pH unit around the protein’s pI. At the pH of the abomasum of 2-3, the proteins re-solubilised again, presumably by increase in their net charge. Due to their ability to form water insoluble complexes, PhT could improve ruminal fermentation in vitro in a dose dependent manner, resulting in lower methane production and ammonia (NH3) concentration. The decreased NH3 concentration reflected decreased dietary protein breakdown in the rumen, which is considered a nutritional and environmental benefit.

Sugar beet leaves for functional ingredients
Tamayo Tenorio, Angelica - \ 2017
University. Promotor(en): Remko Boom, co-promotor(en): Atze Jan van der Goot. - Wageningen : Wageningen University - ISBN 9789463431378 - 188
sugarbeet - leaves - thylakoids - cellulosic fibres - food - surface proteins - food crops - protein extraction - suikerbieten - bladeren - thylakoïden - cellulosevezels - voedsel - oppervlakte-eiwitten - voedselgewassen - eiwitextractie

Plant leaves are recognised as a potential source for food applications based on their nutritional profile and interesting technological properties of leaf components, and based on the large availability of plant leaves in agricultural waste streams. Besides proteins, leaves have a rich nutritional profile (e.g. dietary fibres, minerals and secondary metabolites) and consist of complex biological structures (e.g. chloroplastic membranes) that can be explored as novel fractions that ultimately broaden the use of leaves. The overall aim of this thesis is to explore green leaves as a food source, with emphasis on neglected leaf fractions. This thesis describes a processing approach that aims at separating/generating enriched- functional fractions rather than pure components, and highlights the implications for value creation out of green leaves. The extraction of leaf membrane proteins is investigated using a proteomics extraction method, while the properties of other valuable leaf components (complexes and fibres) are analysed for techno-functional applications. Furthermore, the feasibility of leaves as a food source is studied at an industrial scale, considering large scale processing and options for leaf stabilisation.

The extraction of proteins from sugar beet leaves is evaluated in Chapter 2 by using a traditional heat coagulation method. The heat treatment is thought to precipitate the insoluble proteins together with fibres, chlorophyll and other components, resulting in a green curd. Therefore, the distribution of soluble and insoluble proteins was followed along the extraction process to discern the effect of the heating step on protein fractionation. This study showed that both soluble and insoluble protein distribute almost evenly over the leaf fractions juice, pulp, supernatant and final pellet. The even distribution of the proteins was attributed to the anatomy of leaves and their biological function, which is predominantly the enzymatic activity related to photosynthesis instead of protein storage, which occurs in other plant tissues. This chapter further concludes that striving for high purity severely compromises the yield, and consequently results in inefficient use of the leave proteins.

Chapter 3 describes the application of proteomic analytical extraction protocols to analyse the fractionation behaviour of leaf proteins. This analysis lead to the translation into food- grade processes based on four fundamental extraction steps: (1) tissue disruption, (2) enzymatic inhibition, (3) removal of interfering compounds, and (4) protein fractionation and purification. Part of these extraction steps can be translated into food-grade alternatives, while the processing conditions determine the potential properties for food of the final products. Nevertheless, it was concluded that harsh and/or non-food grade conditions were required to isolate the leaf membrane proteins with high purity. Those results were explained by the fact that membrane proteins are heterogeneous w.r.t. charge, hydrophobicity, post- translational modification and complexation, leading to non-selective behaviour when compared with a single pool of proteins.

Given the large challenges in isolating membrane proteins from leaves, we studied another approach in which green leaves are considered as a source of naturally structured elements that have relevant techno-functional properties for food products, like the chloroplastic membranes (i.e. thylakoid membranes) and cellulose-rich fibres. Chapter 4 describes the properties of thylakoid membranes and their emulsifying mechanism. These membranes showed surface active properties and their adsorption kinetics were typical for large molecules or soft particles. The thylakoid fragments can effectively stabilise emulsion droplets, even though aggregation was observed already during emulsion preparation and increased with increased thylakoid concentration. Both composition and structure make thylakoid membranes suitable as a biobased material for food and pharma applications.

To continue exploring valuable fractions from leaves, Chapter 5 reports on the interfacial behaviour of cellulose-rich particles obtained from leaf pulp. Cellulosic particles were produced from the pulp obtained after leaf pressing. The particles spontaneous adsorption onto the oil-water interface and interfacial behaviour similar to that of solid particles. Addition of cellulosic particles to oil-in-water emulsions resulted in stable emulsions above a particle concentration of 0.1 w/v%, although phase separation was observed. The particle fines (0.04 – 1.0 µm) stabilised the droplet interface, while large particles formed a network in the continuous phase and rendered a top (green) phase in the emulsions. Finding applications for leaf side streams, like leaf pulp, broadens the options for total leaf processing and contributes to resource use optimisation.

A sustainability assessment of leaf processing is discussed in Chapter 6, considering the challenges that may appear at industrial scale. The seasonal availability of sugar beet plants implies the need of processing large amounts of biomass within a short time due to their high moisture content (85 - 90%) and their sensitivity to spoilage. Processing options were evaluated on their resource use efficiency in terms of energy requirement and exergy indicators. A decentralised process constitutes a good option compared to freezing, since solid side streams can be directly returned the land, leaving nutrients to the soil, and reducing transportation loads. With a decentralised process, freezing of the leaves becomes unnecessary; the leaf juice is transported while chilled, resembling the transportation of fresh milk that is also chill-transported from the farm to a central factory.

Chapter 7 concludes this thesis with a general discussion of the main findings. An integrated process for leaf valorisation is described, which combines the production of functional fractions with the production of bulk products such as protein-rich and fibre-rich fractions. A compilation of data on protein yield and protein purity of fractions obtained from protein crops (e.g. soy, lupine beans, pulses) and from photosynthetic active tissues (e.g., leaves, algae, duckweed) is included. Protein crops reach 50 - 60% protein yield with a protein purity of ~ 90%, whereas leaves and other photosynthetic active tissues reach similar protein purity (60 – 80 w/w% protein) but at much lower yields (10%). We hypothesize that the low yields are due to the small length scale in which protein is structured inside the leaves and the lack of protein storage anatomy in these tissues. Therefore, we conclude that leaf valorisation requires non-conventional approaches that go beyond higher extraction yields but that consider a complete use of the biomass.

Dynamic photosynthesis under a fluctuating environment: a modelling-based analysis
Morales Sierra, Alejandro - \ 2017
University. Promotor(en): Paul Struik; Jaap Molenaar, co-promotor(en): Xinyou Yin; Jeremy Harbinson. - Wageningen : Wageningen University - ISBN 9789463430456 - 282
photosynthesis - modeling - analysis - environmental factors - light - canopy - leaves - crop physiology - metabolism - fotosynthese - modelleren - analyse - milieufactoren - licht - kroondak - bladeren - gewasfysiologie - metabolisme

In their natural environment, leaves are exposed to rapid fluctuations of irradiance. Research on CO2 assimilation under fluctuating irradiance often relies on measurements of gas exchange during transients where irradiance is rapidly increased or decreased, after the leaf has adapted to a particular set of environmental conditions. In the field, such increases and decreases occur mostly because of sunflecks (rapid increases in irradiance on a low irradiance background) created by gaps in the canopy and plant movement by wind, and cloudflecks (rapid decreases in irradiance on a high irradiance background) generated by clouds that transiently block the sun.

In this dissertation, the metabolic regulation of photosynthesis and how this may limit dynamic CO2 assimilation is studied in silico with the development and application of simulation models. In order to support the development of the models, a review of the literature was performed as well as an experiment designed to generate data on dynamic CO2 assimilation for different photosynthetic mutants of Arabidopsis thaliana. In addition to providing these models to the research community, this dissertation also identifies multiple targets that may be used for improving dynamic CO2 assimilation in plants. It further demonstrates that the dynamic responses of CO2 assimilation to changes in irradiance has a significant effect on canopy CO2 assimilation, even for dense canopies exposed to open skies, resembling the conditions of commercial crops.

In Chapter 1, the context of this dissertation is presented. The societal relevance of this research is argued, making reference to the role that photosynthesis could play in addressing global problems such as food and energy security. The necessary background on the physiology of photosynthesis is provided, with special emphasis on the terminology and concepts required to understand the rest of the dissertation, with the aim of making the contents more accessible to a wider audience. Then, prior literature on the specific topics of this dissertation (i.e., photosynthesis in a dynamic environment and its mathematical modelling) is presented, with a chronological approach that analyses the evolution of ideas and methodologies up to the present.

In Chapter 2, the current literature on dynamic CO2 assimilation is reviewed, with an emphasis on the effects of environmental conditions ([CO2], temperature, and air humidity) on the rates of photosynthetic induction and loss of induction. This review reveals major knowledge gaps, especially on the loss of induction. The little data available indicates that rates of photosynthetic induction increase with [CO2], which could be explained by a weak effect on Rubisco activation and a strong effect on stomatal opening. Increases in temperature also increase the rates of photosynthetic induction, up to an optimum, beyond which a strong negative effect can be observed, which could be attributed to deactivation of Rubisco activase.

In Chapter 3, an experiment is presented that makes use of several photosynthetic mutants of A. thaliana. Downregulating non-photochemical quenching and sucrose synthesis did not have any significant effect on dynamic CO2 assimilation, whereas CO2 diffusion and Rubisco activation exerted stronger limitations. Further analysis reveals that whether stomatal opening limits CO2 assimilation after an increase in irradiance depends on the stomatal conductance prior to the change in irradiance. A threshold value of 0.12 mol m−2 s−1 (defined for fluxes of water vapour) could be defined, above which stomata did not affect the rates of photosynthetic induction. The comparison of measurements across irradiance levels also indicated that the apparent rate constant of Rubisco activation is irradiance-dependent, at least for irradiance levels below 150 μmol m−2 s−1.

In Chapter 4, a phenomenological model of leaf-level CO2 assimilation is presented. The model is described in detail and all the parameters are first estimated with published data, and later refined by fitting the model to the data from Chapter 3. Additional data from the experiment in Chapter 3 is used to validate predictions of CO2 assimilation under lightflecks for the different photosynthetic mutants. The model predicts accurately dynamic CO2 assimilation for the different photosynthetic mutants by only modifying those parameters that are affected by the mutation. This demonstrates that the model has a high predictive power and that the equations, although phenomenological in nature, have a solid physiological basis.

The model is further used to analyse, in silico, the limitations imposed by different photosynthetic processes on dynamic CO2 assimilation at the leaf and canopy level, allowing a more in depth analysis than in Chapter 3. The analysis demonstrates that results obtained at the leaf level should not be extrapolated directly to the canopy level, as the spatial and temporal distribution of irradiance within a canopy is more complex than what is achieved in experimental protocols. Both at the leaf and canopy level, CO2 diffusion is strongly limiting, followed by photoinhibition, chloroplast movements and Rubisco activation.

In Chapter 5, a mechanistic model of the dynamic, metabolic regulation of the electron transport chain is presented. The model is described in detail and all the parameters are estimated from published literature, using measurements on A. thaliana when available. Predictions of the model are tested with steady-state and dynamic measurements of gas exchange, chlorophyll fluorescence and absorbance spectroscopy on A. thaliana, with success.

The analysis in silico indicates that a significant amount of alternative electron transport is required to couple ATP and NADPH production and demand, and most of it is associated with nitrogen assimilation and export of redox power through the malate shuttle. The analysis also reveals that the relationship between ATP synthesis and the proton motive force is highly regulated by the concentrations of substrates (ADP, ATP and inorganic phosphate), and this regulation facilitates an increase in non-photochemical quenching under conditions of low metabolic activity in the stroma.

In Chapter 6, the findings of Chapters 2–5 are summarised and employed to answer in detail the four research questions formulated in Chapter 1. Of great interest is the identification of six potential targets that may be used to improve dynamic CO2 assimilation. These targets are: (i) regulation of Rubisco activity through changes in the amount or regulation of Rubisco activase, (ii) acceleration of stomatal opening and closure, (iii) a lower /ATP for ATP synthesis, (iv) faster relaxation of non-photochemical quenching, (v) reduced chloroplast movements, and (vi) reduced photoinhibition by increased rates of repair of Photosystem II.

Super-performance in a palm species
Jansen, Merel - \ 2016
University. Promotor(en): Niels Anten; Pieter Zuidema, co-promotor(en): Frans Bongers; M. Martínez-Ramos. - Wageningen : Wageningen University - ISBN 9789462579996 - 193
chamaedorea elegans - understorey - tropical forests - spatial variation - leaves - growth - population ecology - defoliation - genetic variation - onderlaag - tropische bossen - ruimtelijke variatie - bladeren - groei - populatie-ecologie - ontbladering - genetische variatie

The world is changing rapidly due to anthropogenic disturbance. Effects include: global warming, massive pollution, a changed global nitrogen cycle, high rates of land-use change, and exotic species spread. This has a tremendous impact on both natural and agricultural systems. To understand these impacts, good understanding of ecological systems and underlying drivers is necessary. Ecological systems can be studied at different levels of aggregation. Different levels of aggregation influence each other and are also influenced by external drivers like the environment. The population level is of particular interest, because many important ecological processes occur at the population level, like evolution, extinction, and invasion. Ecologists are increasingly recognizing that population processes are strongly influenced by one level of aggregation lower, the individual level. Individual heterogeneity (i.e. differences between individuals in performance), determines many population processes including population growth rate. However, the exact relations between individual heterogeneity, the external drivers of it, and the population level are not always well understood. Furthermore, methods to analyze these relations are not always available.

Individual heterogeneity occurs at different temporal scales, ranging from short- to long-term performance differences between individuals, where short- and long-term refer to the expected lifespan of the species in question. Short-term differences between individuals are relatively easily identifiable and are common in almost all species. But long-term differences are much harder to determine especially for long-lived organisms. Long-term differences between individuals in reproduction have been identified for several animal species, and in growth for several tree species, but less is known about the existence of such differences in other life forms (e.g. palms, lianas or clonal plants). Quantifying the extent to which individuals differ is essential for understanding the influence of individual heterogeneity on population processes. Super-performing individuals (i.e. individuals that persistently grow faster and reproduce more than others), probably contribute more to the growth of the population and therefore to future generations. Future populations will, therefore, have the genetic characteristics of the super-performers. Which characteristics this will be, depends on the genetic and environmental drivers of super-performance. Full understanding of the influence of individual heterogeneity on population processes, therefore, requires knowledge of the underlying causes of individual heterogeneity.

For many species, it is known that spatial variation in environmental conditions can cause short-term performance differences between individuals, but it is often not clear if the same environmental factors that cause short-term performance differences are also the environmental factors that cause long-term performance differences. Furthermore, genetic variation is known to cause performance differences, but to what extent is not well studied in natural long-lived plant populations. Within-population genetic variation can be maintained in habitats that are characterized by strong temporal or spatial heterogeneity in environmental conditions if the performance of a genotype relative to others depends on the environment it experiences.

Super-performing individuals possibly play an important role in the resistance and resilience of populations to disturbance (i.e. maintaining and recovering population growth rate under stress), because super-performers potentially contribute more to the recovery of the population. However, this depends on the relative tolerance to disturbance of super-performers compared to under-performers. A positive relation between performance and tolerance would make super-performers more important, while a negative relation would make them less important. Many types of disturbances entail leaf loss and tolerance to leaf loss is associated with performance being larger than what one would assume based on the amount of leaf area loss. Tolerance can be achieved by compensating for leaf loss in terms of growth rate, which entails either allocating more new assimilates to leaves, allocating new assimilates more efficiently to leaf area (i.e. by increasing specific leaf area), or growing faster with existing leaf area (i.e. by increasing net assimilation rate). Genetic variation in tolerance and compensatory responses would allow populations to adapt to changes in disturbance events that entail leaf loss.

Individual heterogeneity could also have implications for management. Plant and animal populations are managed at many different levels ranging from harvest from natural populations to modern agricultural practices. When harvesting from natural populations, it might be beneficial to spare the individuals that are most important for future production. Individuals could be spared, either because they contribute most to population growth, because they are tolerant to harvesting (which is relevant when only part of a plant is harvested), or when they start producing less or lower quality product. The productivity of natural populations could also be increased by actively promoting those environmental conditions and genotypes that allow for high productivity, which is the basis of agriculture and common practice in forest management. To determine how this can best be done, knowledge of the causes of individual heterogeneity is necessary.

The general aim of this thesis is to identify and quantify the mechanisms that determine individual heterogeneity and to determine how this heterogeneity, in turn, affects population level processes. This aim was divided into four main questions that I addressed: (1) To what extent do individuals differ in performance? (2) What causes individual heterogeneity in performance? (3) What are the demographic consequences of individual heterogeneity? (4) Can individual differences be used to improve the management of populations? To answer these questions, we used the tropical forest understorey palm Chamaedorea elegans as a study system, of which the leaves are an important non-timber forest product that is being used in the floral industry worldwide. We collected demographic data, measured spatial variation in environmental conditions, and applied a defoliation treatment to simulate leaf harvesting, in a natural population in Chiapas, Mexico. Furthermore, we grew seedlings from different mothers from our study population in the greenhouses of Wageningen University, where we also applied a defoliation treatment.

In Chapter 2 we quantified the extent to which individuals differ in long-term growth rate, and analyzed the importance of fast growers for population growth. We reconstructed growth histories from internodes and showed that growth differences between individuals are very large and persistent in our study population. This led to large variation in life growth trajectories, with individuals of the same age varying strongly in size. This shows that not only in canopy trees but also in species in the light limited understorey growth differences can be very large. Past growth rate was found to be a very good predictor of current performance (i.e. growth and reproduction). Using an Integral Projection Model (i.e. a type of demographic model) that was based on size and past growth rate, we showed that fast-growing individuals are much more important for population growth than others: the 50% fastest growing individuals contributed almost two times as much to population growth as the 50% slowest growing individuals.

In Chapter 3 we analyzed the extent to which observed long-term growth differences can be caused by environmental heterogeneity. Short-term variation in performance was mainly driven by light availability, while soil variables and leaf damage had smaller effects, and spatial heterogeneity in light availability and soil pH were autocorrelated over time. Using individual-based simulation models, we analyzed the extent to which spatial environmental heterogeneity could explain observed long-term variation in growth, and showed that this could largely be explained if the temporal persistence of light availability and soil pH was taken into account. We also estimated long-term inter-individual variation in reproduction to be very large. We further analyzed the importance of temporal persistence in environmental variation for long-term performance differences, by analyzing the whole range of values of environmental persistence, and the strength of the effect of the environmental heterogeneity on short-term performance. We showed that long-term performance differences become large when either the strength of the effect of the environmental factor on short-term performance is large, or when the spatial variation in the environmental factor is persistent over time. This shows that an environmental factor that in a short-term study might have been dismissed as unimportant for long-term performance variation, might, in reality, contribute strongly.

In Chapter 4 we tested for genetic variation in growth potential, tolerance to leaf loss, compensatory growth responses, and if growth potential and tolerance were genetically correlated in our study population. We quantified compensatory responses with an iterative growth model that takes into account the timing of leaf loss. Genetic variation in growth potential was large, and plants compensated strongly for leaf loss, but genetic variation in tolerance and compensatory growth responses was very limited. Growth performances in defoliated and undefoliated conditions were positively genetically correlated (i.e. the same genotypes perform relatively well compared to others, both with and without the stress of leaf loss). The high genetic variation in growth potential and the positive correlation between treatments suggests that the existence of super-performing individuals in our study population likely has (at least in part) a genetic basis. These super-performing individuals, that grow fast even under the stress of leaf loss, possibly contribute disproportionately to population resistance and resilience to disturbance. The low genetic variation in tolerance and compensatory responses, however, suggests that populations might have limited ability to adapt to changes in disturbance regimes that entail increases in leaf loss. Furthermore, the high genetic variation in growth potential could potentially be used in management practices like enrichment planting.

In Chapter 5 we explore the potential of using individual heterogeneity to design smarter harvest schemes, by sparing individuals that contribute most to future productivity. We tested if fast and slow growers, and small and large individuals, responded differently to leaf loss in terms of vital rates, but found only very limited evidence for this. Using Integral Projection Models that were based on stem length and past growth rate, we simulated leaf harvest over a period of 20 years, in several scenarios of sparing individuals, which we compared to “Business as usual” (i.e. no individuals being spared, BAU). Sparing individuals that are most important for population growth, was beneficial for population size (and could, therefore, reduce extinction risk), increased annual leaf harvest at the end of the simulation period, but cumulated leaf harvest over 20 years was much lower compared to BAU. Sparing individuals that produced leaves of non-commercial size (i.e. <25cm), therefore allowing them to recover, also resulted in a lower total leaf harvest over 20 years. However, a much higher harvest (a three-fold increase) was found when only leaves of commercial size were considered. These results show that it is possible to increase yield quality and sustainability (in terms of population size) of harvesting practices, by making use of individual heterogeneity. The analytical and modeling methods that we present are applicable to any natural system from which either whole individuals, or parts of individuals, are harvested, and provide an extra tool that could be considered by managers and harvest practitioners to optimize harvest practices.

In conclusion, in this thesis, I showed that in a long-lived understorey palm growth differences are very large and persistent (Chapter 2) and that it is likely that long-term differences in reproduction are also very large (Chapter 3). I also showed that spatial heterogeneity in environmental conditions can to a large extent explain these differences and that when evaluating the environmental drivers of individual heterogeneity, it is important to take the persistence of spatial variation into account (Chapter 3). Individual heterogeneity also is partly genetically determined. I showed that genetic variation in growth potential to be large (Chapter 4), and that fast growers keep on growing fast under the stress of leaf loss (Chapters 4,5). Therefore it is likely that genetic variation contributes to long-term differences between individuals. Genetic variation for tolerance and compensatory responses was estimated to be low (Chapter 4), suggesting that the adaptive potential of our study population to changes in disturbance events that entail leaf loss might be low. I also showed that super-performing individuals are much more important for the growth of the population (Chapter 2) and that individuals that are important for future production could be used to improve the management of natural populations (Chapter 5).

This study provides improved insight into the extent of individual heterogeneity in a long-lived plant species and its environmental and genetic drivers, and clearly shows the importance of individual heterogeneity and its drivers for population processes and management practices. It also presents methods on how persistent performance differences between individuals can be incorporated into demographic tools, how these can be used to analyze individual contributions to population dynamics, to extrapolate short-term to long–term environmental effects, and to analyze smart harvesting scenarios that take differences between individuals into account. These results indicate that individual heterogeneity, underlying environmental and genetic drivers, and population processes are all related. Therefore, when evaluating the effect of environmental change on population processes, and in the design of management schemes, it is important to keep these relations in mind. The methodological tools that we presented provide a means of doing this.

Arriving at the right time : a temporal perspective on above-belowground herbivore interactions
Wang, Minggang - \ 2016
University. Promotor(en): Wim van der Putten, co-promotor(en): T.M. Bezemer; A. Biere. - Wageningen : Wageningen University - ISBN 9789462578142 - 174 p.
herbivores - aboveground belowground interactions - herbivory - defence mechanisms - roots - leaves - mycorrhizas - population dynamics - soil biology - herbivoren - boven- en ondergrondse interacties - herbivorie - verdedigingsmechanismen - wortels - bladeren - mycorrhizae - populatiedynamica - bodembiologie
Leaf anatomy and photosynthesis : unravelling the CO2 diffusion pathway in C3 leaves
Berghuijs, H.N.C. - \ 2016
University; KU Leuven. Promotor(en): Paul Struik; Bart M. Nicolaï, co-promotor(en): Xinyou Yin. - Wageningen : Wageningen University - ISBN 9789462577947 - 286 p.
leaves - plant anatomy - photosynthesis - mesophyll - photorespiration - carbon pathways - solanum lycopersicum - bladeren - plantenanatomie - fotosynthese - bladmoes - fotorespiratie - koolstofpathways

Keywords: CO2 diffusion, C3 photosynthesis, mesophyll conductance, mesophyll resistance, re-assimilation, photorespiration, respiration, tomato

Herman Nicolaas Cornelis Berghuijs (2016). Leaf anatomy and photosynthesis; unravelling the CO2 diffusion pathway in C3 leaves. PhD thesis. Wageningen University, Wageningen, The Netherlands, with summaries in English and Dutch. 286 pages

Optimizing photosynthesis can contribute to improving crop yield, which is necessary to meet the increasing global demand for food, fibre, and bioenergy. One way to optimize photosynthesis in C3 plants is to enhance the efficiency of CO2 transport from the intercellular air space to Rubisco. The drawdown of CO2 between these locations is commonly modelled by Fick's first law of diffusion. This law states that the flux from the air spaces to Rubisco is proportional to the difference in partial pressure between these locations. The proportionality constant is the mesophyll conductance. Its inverse is mesophyll resistance. Mesophyll resistance is a complex trait, which lumps various structural barriers for CO2 transport and processes that add or remove CO2 along the diffusion pathway. In order to better understand how and to what extent these factors affect photosynthesis, it is necessary to find a more mechanistic description of CO2 transport in the mesophyll. The aim of this dissertation is to investigate how leaf anatomical properties and CO2 sources and sinks along the CO2­ diffusion pathway in C3 leaves affect the photosynthetic capacity of these leaves. In this study, Solanum lycopersicum was used as a model organism. In a first approach, we developed a model in which we partitioned mesophyll resistance into two sub-resistances. The model assumed that CO2 produced by respiration and photorespiration was released between the two sub-resistance components. By quantifying these resistances using measured thicknesses, exposed mesophyll and chloroplast surfaces, and assumed diffusive properties, we were able to simulate the effect of various anatomical properties on photosynthesis. A disadvantage of this two-resistance approach is that it assumes either that (photo)respiratory CO2 release takes place in the outer cytosol or that there is no CO2 gradient in the cytosol. Therefore, in a second approach we modelled CO2 transport, production and consumption by use of a reaction-diffusion model. This model is more flexible in terms of determining the location of CO2 sources and sinks. We developed methods to estimate physiological parameters of this model using combined gas exchange and chlorophyll fluorescence measurements on leaves. The results suggest that the rate of respiration depends on the oxygen partial pressure, which is often not considered in previous photosynthesis models. We also presented a method to calculate the fraction of (photo)respiratory CO2 that is re-assimilated. We found that this fraction strongly depends on both environmental factors (CO2, irradiance), the location of mitochondria relative to the chloroplast, stomatal conductance and various physiological parameters. The reaction-diffusion model and associated methods presented in this study provide a more mechanistic framework to describe the CO2 diffusion pathway in C3 leaves. This model could, therefore, contribute to identifying targets to increase mesophyll conductance in future research.

Biorefinery of leafy biomass using green tea residue as a model material
Zhang, C. - \ 2016
University. Promotor(en): Johan Sanders, co-promotor(en): Marieke Bruins. - Wageningen : Wageningen University - ISBN 9789462576902 - 156 p.
biorefinery - biomass conversion - leaves - biomass - green tea - tea - alkaline pulping - pectins - lignocellulose - environmental impact - processes - plant protein - food - biobased economy - bioraffinage - biomassaconversie - bladeren - biomassa - groene thee - thee - alkalische pulpbereiding - pectinen - milieueffect - processen - plantaardig eiwit - voedsel

Summary

With the rapidly growing world population and improving living standards, food demand is increased with a simultaneous desire for less human impact on the environment, such that “Twice the food production at half the ecological footprint” could be the EU goal for 2050. In fact, a boost in food demand is mainly required in developing countries, where the farmlands are limited and/or they are of poor quality. Rather than improving crop-production yield, developing biorefinery technology with unused biomass, such as leaves, in developing countries may be the key to fulfil the food demand.

Four major components, protein, pectin, lignin, and (hemi-) cellulose, account for more than 70% of the materials in leaves in almost all species. Among these components, protein and pectin can be used in food and animal feed, and they are key components for supplementing food production. However, the production and application of leaf products is limited for four reasons: unstable raw materials, complex components, rigid plant cell walls, and underdeveloped leaf logistics and economics. The limitations cause low pectin and protein yields, and low cost-efficiency in current extraction technologies, including mechanical milling, chemical extraction (acid and alkaline), solvent extraction, and ammonia protein extraction. Development of an integrated process for multiple products might be a good option for leaf biorefinery, but the compatibilities of these processes were unknown.

The aim of this study was to develop new processes and applications that optimally utilize all components, particularly protein, of leafy biomass in the feed and/or food industry using green tea residues as a starting material. The method should also be applicable to other leafy biomass. The research started from the development of alkaline protein extraction technology as presented in Chapter 2. We found that in alkaline protein extraction, temperature, NaOH amount, and extraction time are the parameters determining protein yield, while pH and volume of extraction liquid are critical parameters for production cost. After optimization, more than 90% of leaf protein could be extracted at a cost of 102€/ton protein by single step alkaline extraction. The extracted protein nutritional value was comparable to soybean meal and this technique can be adapted to various leafy biomass. Main drawback of this technique is the overuse of alkali, generation of salts, and the destruction of key amino acids, such as lysine, during the extraction. We tried to overcome its drawbacks by developing integrated process with a recycle for chemicals.

Chapter 3, 4, 5, and 6 refer to the integrated biorefinery. For a better design, we investigated how the alkali aided protein extraction (Chapter 3), and proved that alkaline protein extraction was not facilitated by increased solubility or hydrolysis of protein, but positively correlated to leaf tissue disruption. HG pectin, RGII pectin, polyphenols, and organic acids can be extracted before protein. Protein extraction can then be followed by the extraction of cellulose and hemi-cellulose. RGI pectin and lignin yield were both linearly correlated to protein yield, which indicated that they are likely to be the key limitation to leaf protein extraction. Based on the above findings, an integrated biorefinery that combined protein extraction with a pre-treatment was proposed. In Chapter 4, ethanol, viscozyme, and H2O2 were selected for pre-treatments targeting on the removal of polyphenols and pigments, carbohydrates, and lignin accordingly. Ethanol and viscozyme could extract their targeting components efficiently while H2O2 could bleach GTR with no lignin extracted. The best pre-treatment was the combination of viscozyme and 50% ethanol extraction, which not only reduced the use of alkali by 50%, but also improved protein content and its nutritional value. As pectin can be applied for food or chemicals, enzyme and PBS buffer were investigated for pectin extraction (Chapter 5). Both enzyme and PBS buffer extraction could not only extract high yield HG pectin (predominated by galacturonic acid) with no protein extraction, but also reduced alkali usage in subsequent protein extraction. Pectin obtained using PBS buffer could be present in its native form, which can be precipitated by 40% ethanol. Buffer is suggested to extract pectins when pectins are to be used in food. Otherwise, hydrolyzed pectin that mainly contains galacturonic acid, can be converted to other useful chemicals. For this the enzymatic methods, such as using Viscozyme® L, are recommended.

Alkali usage was further optimized. It was found that by using potassium hydroxide, the protein extraction efficiency was similar to that using sodium hydroxide. The waste water, mainly containing potassium salts, can then be used as fertilizer. This technique is highly depending on the location of factories, which should be built close to the field. Alternatively, calcium hydroxide can be used. As calcium salts can be precipitated by CO2 and calcium hydroxide can be regenerated through burning of the precipitate, this scheme is sustainable and adaptable to most situations. However, as calcium also precipitated pectin, ployphenols, and even proteins, the protein yield is relatively low. Although a pre-treatment can improve extraction efficiency of calcium hydroxide, economic results suggested that a pre-treatment is not necessary unless the products obtained by pre-treatment have an attractive market value.

In Chapter 7, we extend our knowledge on leaf biorefinery with some additional experiments and literature. Simplified models of leaf tissues and cell walls were proposed and used to explain the mechanism of alkaline protein extraction. The models were also used to explain other mechanisms for protein extraction; mechanical milling, steam explosion, acid, and enzyme aided extraction. The possible improvements of leaf biorefinery economics were illustrated either by reducing production cost, by e.g. using counter current extraction or ultrafiltration, or by upgrading product value by applying protein and pectin in food. The processes recommended in this thesis show an excellent prospective, in which they are applicable to other leaf biomass and suitable for small-scale production.

Linking leaf initiation to the aerial environment: when air temperature is not the whole story
Savvides, A. - \ 2014
University. Promotor(en): Leo Marcelis, co-promotor(en): Wim van Ieperen; Anja Dieleman. - Wageningen : Wageningen University - ISBN 9789462571136 - 154
bladeren - plantenontwikkeling - initiatie - knoppen - bladmeristemen - licht - luchttemperatuur - leaves - plant development - initiation - buds - leaf meristems - light - air temperature

The initiation of new leaves, which takes place at the shoot apical meristem, is essential for plant growth and development. Leaf initiation rate (LIR) is very sensitive to meristem temperature. However, in practice meristem temperature is hardly ever monitored and air temperature is often used instead. It can be questioned whether relating LIR solely to air temperature is valid. This thesis aims at linking LIR to the aerial environment in two main horticultural crops: tomato and cucumber. It was shown that meristem temperature often differs from air temperature, depending on other environmental factors (e.g. radiation, humidity and wind speed) and species-specific traits. LIR was solely influenced by meristem temperature even when it largely deviated from air temperature. In addition, LIR was reduced at low light levels. Consequently, air temperature is not the whole story when relating leaf initiation to the environment.

Coniferous needle-leaves, shots and canopies : a remote sensing approach
Yanez Rausell, L. - \ 2014
University. Promotor(en): Michael Schaepman, co-promotor(en): Z. Malenovsky; Jan Clevers. - Wageningen : Wageningen University - ISBN 9789461738684 - 154
remote sensing - naaldbossen - pinopsida - naalden, coniferen - bladeren - optische eigenschappen - modellen - coniferous forests - conifer needles - leaves - optical properties - models

Coniferous forests are important in the regulation of the Earth’s climate and thus continuous monitoring of these ecosystems is crucial to better understand potential responses to climate change. Optical remote sensing (RS) provides powerful methods for the estimation of essential climate variables and for global forest monitoring. However, coniferous forests represent challenging targets for RS methods, mainly due to structural features specific for coniferous trees (e.g. narrow needle leaves, shoot clumping) whose effects on the RS signal are not yet known or not yet fully understood.

Recognizing the need for a better adaptation of RS methods to such spatially heterogeneous and structurally complex canopies, this thesis contributes to improving the interpretation of the remotely sensed optical signal reflected from coniferous stands by focusing on specific knowledge gaps identified in the RS methods at different scales of the coniferous canopies. In addition, it explores the application of approaches that simplify the way the structural complexity of such an environment is tackled when using canopy-level radiative transfer approaches. Three main levels based on the identified gaps were defined for the analysis: (needle) leaf level (chapter 2 and 3); shoot level (chapter 4) and canopy level (chapter 5).

At leaf levelthis thesis contributes to minimizing the uncertainties and errors related to leaf optical measuring methods adapted for needle leaves. Although optical properties of coniferous leaves are extensively used in RS approaches (i.e. as input or as validation data), there is only a limited number of techniques available for measuring coniferous leaves. The first focus of this thesis was to review the shortcomings and uncertainties of such methods in order to identify application limits and potential improvements (chapter 2). A review showed that a more standardized measuring protocol was needed, for which measurement uncertainties and errors had to be identified, quantified and preferably removed or minimized. Thus, an experimental set-up improving the original method of Mesarch et al. (1999) was presented (chapter 3), which focused on analyzing uncertainties caused by the presence of the sample holder and by the multiple scattering triggered by both the shape of the specific needle cross-section, and the distance between the needles composing a sample. Results showed that both the sample holder and the multiple scattering, triggered specially by the shape of the non-flat cross section of the coniferous needle-leaves, had a non-negligible effect on the optical signal when measured using a standard spectroradiometer coupled to a single-beam integrating sphere and following the method suggested by Mesarch. Thus, approaches designed to measure optical properties of non-flat coniferous needle samples more comprehensively should take into account these effects in their current signal correction algorithms.

Needle clumping into shoots quickly transforms the optical signal making the description of the canopy radiative transfer a complex task and encouraging the search for simplified yet robust approaches. Thus, subsequent steps in this thesis focus on one such simplified approach, known as the recollision probability theory (“p-theory”), applied at two hierarchical levels, i.e., shoots (Chapter 4) and the whole canopy (Chapter 5).At shoot level, an empirical verification of the relationship between the photon recollision probability and a structural parameter called STAR was investigated. The approach allows upscaling needle albedo to shoot albedo and was previously theoretically tested only (chapter 4). For this analysis empirical optical measurements of Scots pine needles and shoots were used. Results showed that the approach works well for the VIS and SWIR spectral regions. However, it was less accurate for the NIR and also for sparse shoots (STAR <0.15) with an uneven distribution of photon–needle interactions and a larger influence of the twig bark.

Finally, accurate modelling of the reflectance signal at canopy levelfor coniferous canopies requires realistic representations of the forest stands, which in general implies a large number of input parameters and computationally demanding algorithms. Radiative transfer modelling based on the photon recollision probability offers an alternative for a simplified definition of the forest canopy structure. The performance of such approach for estimation of the leaf chlorophyll content from satellite imaging spectroscopy data acquired by the CHRIS-PROBA sensor was investigated. The approach was compared to a computationally more demanding one based on a detailed 3D structural description of a forest (chapter 5). For this purposes two canopy models, PARAS and DART, representing the first and second approach respectively, were used. Top-of-canopy bidirectional reflectance factors (BRF) were simulated for both models and used to calculate two optical indices, ANCB670–720 and ANMB670–720.Subsequently, the empirical relationships established between the optical indices and the needle-leaf chlorophyll content (Cab) were applied to the CHRIS-PROBA image of a Norway spruce forest stand to retrieve a map of Cab estimates. Results showed that for the spatial resolution of CHRIS-PROBA (17 m), the simpler model PARAS can be applied to retrieve plausible needle-leaf Cab estimates from satellite imaging spectroscopy data with less intensive model parameterization and reduced computational powerthan when using a model like DART. The ANMB670–720 optical indexwas more robust andresulted in a linear relationship between the Cab estimated by both models. This relationship showed, however, a systematic offset that is potentially caused by differences in the implementation of woody elements in each model or by a different parameterization of leaf optical properties. Thus, further investigation on the impact of parameterization differences related to the needle optical properties and the implementation of woody elements in such a model is recommended.

LED belichting in Alstroemeria
Helm, F.P.M. van der; Garcia Victoria, N. ; Warmenhoven, M.G. - \ 2014
alstroemeria - cultuurmethoden - winter - belichting - led lampen - gewaskwaliteit - bladeren - gewasproductie - energiebesparing - glastuinbouw - cultural methods - illumination - led lamps - crop quality - leaves - crop production - energy saving - greenhouse horticulture
Winterproductie van Alstroemeria is afhankelijk van belichting voor het voorkomen van knopverdroging. SON-T belichting (50-100 μmol/m²/s) wordt gebruikt tot een daglengte van 16 uur per dag, (kwantitatieve lange dag plant). In de winter is de bladkwaliteit van alstroemeria soms niet goed. Telers vermoeden een rol van belichten. Onderzocht is of LED belichting mogelijk kan bijdragen aan betere bladkwaliteit en productieverhoging bij een lagere stroomvraag.
Bladschade bij potanthurium
Warmenhoven, M.G. ; Garcia Victoria, N. ; Noort, F.R. van - \ 2012
Bleiswijk : Wageningen UR Glastuinbouw (Rapporten GTB 1186) - 86
bladplanten - bladeren - schade - overdosis - kalk - waterbehoefte - vochtgehalte - substraten - anthurium - bladvlekkenziekte - potplanten - foliage plants - leaves - damage - overdose - lime - water requirements - moisture content - substrates - leaf spotting - pot plants
Bladschade bij gevoelige potanthurium cultivars verlaagt de sier-en marktwaarde van het product. De kosten voor de sector bedragen naar schatting 7500 € per ha per jaar. Daarom is met financiering van PT van november 2011 tot mei 2012 onderzoek uitgevoerd naar de mogelijke oorzaken van twee vormen van bladschade bij potAnthurium. Gebleken is dat de necrotische stippen op de bladrand van het oude blad niet altijd overeenkomen met guttatie en/of schade aan de hydathoden. De necrose, een niet omkeerbare schade, wordt ook niet veroorzaakt door calcium gebrek, of mangaan overmaat, in tegengeel, een hogere Calciumgift verergert het schadebeeld. Vlekkerige bladvergeling, een omkeerbare schadevorm is niet het gevolg is van lenswerking van waterdruppels op het blad, maar tekort aan Magnesium of Mangaan verergeren het schadebeeld. Beide schades worden grotendeels voorkomen door te telen in een afwijkende omgeving (onder een folie); door de overgang van een vochtige omgeving (onder een folie) naar een “normale” omgeving ontstaat geleidelijk schade of neemt de aanwezige schade toe. Het telen onder folie kent echter ook negatieve effecten. Aanbevolen wordt daarom om vervolgonderzoek te verrichten naar de relaties tussen de watergeefstrategie en het substraatvocht en het optreden van schade. Abstract Sensitive potanthurium cultivars can show leaf damage that reduce both the ornamental and the market value of the product. The costs for the sector are estimated at € 7,500 per hectare per year. To study the possible causes of two types of leaf damage, a series of activities and experiments were performed between November 2011 and May 2012. It has been found that the necrotic spots on the leaf edge (appearing mainly in older leaves) do not always correspond with guttation and / or damage to the hydathodes. The necrosis, a non reversible damage is not caused by calcium deficiency or excess manganese, on the contrary, a higher calcium supply leads to an increased damage. Yellow spots on the younger leaves, the other type of damage, has proved reversible and is not the result of lensing of water droplets on the leaf. A reduced supply of magnesium or manganese, worsen the damage. Both damage forms have been largely prevented by cultivation in a different environment (under foil), the transition from a humid environment (under foil) to a “normal” environment gradually leads to an increase of the damage symptoms. However, growing under plastic also has negative effects. It is therefore recommended to conduct further research to the influence of the relations between the watering strategy and the substrate moisture and the occurrence of the damage.
Phenology related measures and indicators at varying spatial scales : investigation of phenology information for forest classification using SPOT VGT and MODIS NDVI data
Clerici, N. ; Weissteiner, C.J. ; Halabuk, A. ; Hazeu, G.W. ; Roerink, G.J. ; Mücher, S. - \ 2012
Wageningen : Alterra (Alterra-rapport 2259)
fenologie - bossen - habitats - modellen - bladeren - classificatie - phenology - forests - models - leaves - classification
Transcriptional networks of TCP transcription factors in Arabidopsis development
Danisman, S.D. - \ 2011
University. Promotor(en): Gerco Angenent, co-promotor(en): Richard Immink. - [S.l.] : S.n. - ISBN 9789461730336 - 159
arabidopsis - transcriptie - moleculaire biologie - transcriptiefactoren - bladeren - groei - transcription - molecular biology - transcription factors - leaves - growth

Leaves are a plant’s main organs of photosynthesis and hence the development of this organ is under strict control. The different phases of leaf development are under the control of both endogenous and exogenous influences. In this work we were interested in a particular class of transcription factors known to control leaf development: the TCP transcription factor family. Members of the TCP transcription factor family are found to be involved in transcriptional control of leaf development in different plant species, including tomato, snapdragon and the model plant Arabidopsis thaliana. The 24 TCP genes encoded in the Arabidopsis genome are divided into two classes, class I and class II TCPs. Based on the putative consensus binding sites of TCP proteins belonging to these classes, the theory has been postulated that class I and class II proteins antagonistically regulate common target genes. In general, not much is known about TCP functions, and almost all knowledge comes from analyses of class II TCP mutants, where divergent phenotypes have been characterized in single and multiple gene knockouts. Most of the time, single TCP knockouts have inconspicuous or no divergent phenotypes that can be explained by strong functional redundancy within the TCP transcription factor family. The most prominent example is the JAGGED AND WAVY (JAW) phenotype, in which a group of five TCP transcription factors that are under control of the microRNA miR319a a knocked down by overexpression of the microRNA. Different ways exist to circumvent problems with genetic redundancy. One way is to cross knockout lines for closely related homologues in order to knock-out complete functions. In the TCP family, where sequences are highly variable outside the so called TCP domain, highest sequence homology is not always a good predictor for functional redundancy. Instead, integration of expression and other functional data can help determining the level of functional redundancy between closely related genes. We could show that from the four TCPs that are closely related to TCP4 the transcription factor, TCP10 has the highest overlap in sequence, expression, and protein-protein interaction capacity. Further investigation shows a strong overlap in target genes as well, specifically covering genes that are involved in jasmonate (JA) synthesis and response, indicating common functions and verifying earlier studies on the importance of JA signaling in mediating class II TCP functioning in leaf development. Another way to circumvent genetic redundancy as a problem to analyze gene function, which is suitable for the analysis of transcription factors, is to identify the genes that are under direct transcriptional control of the transcription factor. We identified direct target genes of the class I TCP transcription factor TCP20, because no phenotypic alterations could be observed in tcp20 single knockout mutants. Among the target genes found there was a significant proportion of JA synthesis and response genes. Surprisingly, cell cycle genes, which were supposed to be under the control of TCP20, were not found in our study. Because LIPOXYGENASE2 (LOX2), which is also under the control of the class II TCP transcription factors TCP4 and TCP10, was found to be a target of TCP20 we were able to investigate and partially verify the previously theorized antagonistic control of target genes by class I and class II TCPs. Another group of genes that was found to be over-represented in the TCP20 target gene list were genes involved in iron homeostasis in both roots and leaves. The so called subgroup Ib basic helix-loop-helix transcription factors were analyzed for their role in leaf development. We could show that these transcription factors are involved in photomorphogenesis during the switch from proliferative to differentiated leaf cells, and that they are inhibited by TCP20 as a means to suppress cell differentiation during early leaf development. As TCPs were not found to control the cell cycle directly, we identified potential direct regulators in a large scale analysis of transcription factor binding to three selected cell cycle promoters. Transcription factors of different families were identified, some of which previously have not been associated to cell cycle control. Of these families, especially the MYB and NAC families of transcription factors stand out.

In sum, we found both class I and class II TCPs to be involved in hormonal control of leaf development, but also in cell wall control and iron homeostasis, increasing the number of cellular functions TCPs are probably involved in. More importantly we could not find any indications that core cell cycle genes are direct targets of these transcription factors, despite the growth effects discovered when knocking out several TCP genes. The fact that in these tcp mutants ultimately cell proliferation is affected leads to the assumption that TCP genes indirectly control the cell cycle via downstream targets. For this, especially the hormones under their control are strong candidates. We conclude that the broadly expressed members from the TCP transcription factor family are not the key regulators of growth, but act as co-factors or mediators in this biological process.

Stress in de plant speelt rol bij bladvorming : vervorming blad kost geld door productieverlies of aantasting sierwaarde
Ieperen, W. van - \ 2011
Onder Glas 8 (2011)10. - p. 8 - 9.
snijbloemen - chrysanten - deformatie - bladeren - stress - belichting - plantenfysiologie - lichtregiem - cultuurmethoden - glastuinbouw - cut flowers - chrysanthemums - deformation - leaves - illumination - plant physiology - light regime - cultural methods - greenhouse horticulture
Bladvervorming kost productie en kan de sierwaarde ernstig aantasten. Meer zicht op oorzaken zou dus welkom zijn. Het blijkt een complexe zaak, waarbij waarschijnlijk meerdere effecten door elkaar heen spelen. Daarom vergt een oplossing, bijvoorbeeld voor bolblad bij chrysant, ook een samenspel van maatregelen.
Bladrandjes en Ca bij tomaat: Fysiologische achtergronden van cel- en weefselstevigheid in relatie tot het ontstaan van bladrandjes en infectie met Botrytis cinerea L.
IJdo, M.L. ; Janse, J. ; Hofland-Zijlstra, J.D. ; Voogt, W. - \ 2011
Bleiswijk : Wageningen UR Glastuinbouw (Rapporten GTB 1116) - 48
solanum lycopersicum - botrytis cinerea - bladeren - symptomen - calcium - gebreksziekten - glastuinbouw - leaves - symptoms - deficiency diseases - greenhouse horticulture
Tip burn of tomato leaves is often seen by growers as indication for maximum crop performance, however grey mould (botrytis), can easily infect through the necrotic leaf edges. In this desk study factors that are influencing the occurrence of tip burn and calcium (Ca) deficiency were studied. Cells formed during periods of Ca shortage have weaker membranes and walls and ‘burst’ after a climatic shock resulting in plasmolysis and disintegration of the membranes. Possibly the disruption of the Ca homeostasis in the cytoplasm. Botrytis uses dead tissue as an entrance to infect the plant. The weak cell walls and solute leaking caused by disruption of the membranes facilitates the infection process of the fungus. Ca uptake and transport are affected by high fruit load, EC and K/Ca in the root environment and transpiration and root pressure. These factors sometimes interact and sometimes are independently effective, resulting in a complex situation. Thus preventing heavy fruit loads in susceptible periods and stimulating Ca uptake and distribution will alleviate the problem. This, in combination with the prevention of climate shocks will help to reduce the occurrence of tip burn in tomato.
Onderzoek bolblad chrysant: Resultaten praktijkonderzoek op bedrijven in De Lier en Hoek van Holland
Maaswinkel, R.H.M. ; Ieperen, W. van; Kersten, M. - \ 2011
Bleiswijk : Wageningen UR Glastuinbouw (Rapporten GTB 1079) - 32
chrysanthemum - bladeren - afwijkingen, planten - symptomen - daglicht - kunstmatige verlichting - verrood licht - aanvullend licht - schijnbaar positieve resultaten - glastuinbouw - nederland - leaves - plant disorders - symptoms - daylight - artificial lighting - far red light - supplementary light - false positive results - greenhouse horticulture - netherlands
During the growing season 2010-2011, on two nurseries, research was done on bulbous leaf by chrysanthemum. The amount of daylight is limited during the winter. It is common that the chrysanthemum-plants are lighted by SON-T lamps. The spectrum of these lamps (550 – 620 nanometres) is not corresponding to the daylight. Especially the far-red part of the spectrum is during the winter scarcely present. It supposed that caused by the shortage of far-red light the conversion of starch does not expired optimum at night for varieties which are sensitive for bulbous leaf. The natural shortage of far-red light in the spectrum can be supplemented by lightning with bulbs. On both nurseries standard cultivation is compared with cultivation in which, after a dark period of one hour light is given with bulbs during one hour. On both nurseries there were limited problems with bulbous leaf. Only one time (with the variety Anastasia Pink Star) it was possible to prevent bulbous leaf with given light by bulbs. Further on it appears that delaying of the bud formation was occurred by lighting with bulbs during the dark period.
Kasproef detectie en beheersing van Pseudomonas cattleyae in Phalaenopsis
Ludeking, D.J.W. ; Kromwijk, J.A.M. ; Woets, F. ; Vermunt, A. ; Schenk, M.F. - \ 2010
phalaenopsis - acidovorax avenae - detectie - gewasbescherming - aantasting - bladeren - detection - plant protection - infestation - leaves
Informatieposter over een kasproef detectie en beheersing van Pseudomonas cattleyae in Phalaenopsis
Mogelijkheden om vroeg tijdig bladrandproblemen te signaleren met MIPS bij Hortensia
Noort, F.R. van; Jalink, H. - \ 2010
Bleiswijk : Wageningen UR Glastuinbouw (Rapport / GTB 1027) - 14
gewasbescherming - groeispanning - hydrangea - afwijkingen, planten - potplanten - bladeren - bladvlekkenziekte - fluorescerend licht - meting - plant protection - growth stress - plant disorders - pot plants - leaves - leaf spotting - fluorescent light - measurement
Met geavanceerde camera technieken zijn beelden vast te leggen van fotosynthese activiteit en het is ook mogelijk gebleken om bladgedeelten met stress vast te leggen, zonder dat deze stress met het blote oog al te zien is. Dit opent perspectieven om monitorringonderzoek te doen naar het ontstaan van bladrandschade en tegelijkertijd naar de eventuele mogelijkheden tot ingrijpen met (wellicht) herstel. Deze metingen worden in het donker uitgevoerd. Er is recentelijk een nieuwe camera ontwikkeld die ook in het licht kan meten, maar bij een meting in het licht zal het verschil tussen schade- en gezonde plekken waarschijnlijk kleiner zijn dan bij een meting in het donker. Dit laatste zal getest moeten worden.
Inzicht in het optreden van bolblad bij chrysant
Ieperen, W. van; Maaswinkel, R.H.M. ; Corsten, R. ; Roelofs, T. - \ 2010
Bleiswijk : Wageningen UR Glastuinbouw (Rapport / Wageningen UR Glastuinbouw 326) - 8
chrysanthemum - bladeren - afwijkingen, planten - symptomen - plantenziekten - glastuinbouw - sierteelt - leaves - plant disorders - symptoms - plant diseases - greenhouse horticulture - ornamental horticulture
Jaarlijks treedt vanaf begin november tot en met eind februari op verschillende chrysantenbedrijven bolblad op. Er zijn een aantal chrysanten rassen zeer gevoelig hiervoor. Takken met bolblad hebben een negatieve sierwaarde. Een duidelijke oorzaak is nog niet gevonden. In december 2009 zijn op twee bedrijven in de Bommelerwaard chrysanten met bolblad gemonsterd. Na waarnemingen op de bedrijven blijkt het volgende: 1. De eerste bladeren met bolblad worden al gesignaleerd bij planten in de lange dagperiode. 2. Gedurende de korte dag fase neemt het aantal bladeren met bolblad toe. 3. Na “pluizen” is er een toename van het aantal bladeren met bolblad. Bij het optreden van bolblad wordt gedacht aan de volgende hypothese: Alle planten bouwen gedurende de dag een zetmeelreserve op in bladeren en stengels om de volgende nacht te kunnen overleven. In het donker is er geen fotosynthese en daardoor geen aanmaak van assimilaten. Onderhoudsprocessen in de plant staan echter ’s nachts niet stil en zijn noodzakelijk voor de plant om te kunnen overleven. Planten gebruiken dus ook ’s nacht assimilaten, in het bijzonder voor onderhoud maar ook voor nachtelijke groei. Deze assimilaten komen ’s nachts beschikbaar door zetmeel af te breken. Dit zetmeel wordt overdag opgebouwd. Er is dus een dagelijkse cyclus van opbouw en afbraak van zetmeel in een plant. Planten hebben ingenieuze systemen om opbouw en afbraak van zetmeel op elkaar af te stemmen. Ze reageren op een tekort aan assimilaten aan het einde van de nacht door de daaropvolgende dag meer in licht geproduceerde assimilaten om te zetten in zetmeel en minder in groei. Aan het omgekeerde, een overschot aan zetmeel aan het einde van de nacht, is weinig onderzoek gedaan. In het algemeen wordt aangenomen dat een plant dan het omgekeerde doet: om ophoping van zetmeel te voorkomen worden overdag minder assimilaten naar zetmeel omgezet en kan ook de productie van assimilaten worden verlaagd door efficiëntie van de fotosynthese te verlagen of door de lichtonderschepping te verlagen. Het optreden van bol blad kan worden gezien als het mijden van licht om de fotosynthese te verlagen en daardoor verdere zetmeelophoping te voorkomen. Deze licht-mijding reactie zou het gevolg kunnen zijn van zetmeelophoping in de bladeren met als doel productie en gebruik van assimilaten (en zetmeel) over 24h weer in balans te brengen. Het doel van de ‘scan’ op beide bedrijven was een indruk te krijgen of er zetmeelophoping optreedt in bladeren van belichte chrysant cv ‘Anastasia’ in verschillende teeltfasen en of er een correlatie is met het optreden van ‘bol blad’. Na analyse van de monsters blijkt, dat er sterke zetmeelophoping in de bladeren optreedt gedurende de lange dag fase en op één van de bedrijven na het pluizen in de korte dag. Naast de bemonstering op twee bedrijven is op één chrysantenbedrijf vastgesteld dat daar waar een lagere temperatuur werd gerealiseerd er minder bolblad optrad dan op plaatsen met een hogere ruimtetemperatuur.
Led-licht geeft iets efficientere bladfotosynthese (interview met Jan Snel)
Snel, J.F.H. - \ 2010
Groenten en Fruit Magazine 2010 (2010)2. - ISSN 1879-7318 - p. 50 - 51.
proeven op proefstations - tuinbouwbedrijven - belichting - lichtgevende dioden - fotosynthese - bladeren - kooldioxide - vruchtgroenten - glastuinbouw - led lampen - station tests - market gardens - illumination - light emitting diodes - photosynthesis - leaves - carbon dioxide - fruit vegetables - greenhouse horticulture - led lamps
Planten benutten sommige lichtkleuren efficiënter dan andere. Onderzocht is of die veronderstelde gevoeligheid bij huidige gewassen nog overeenstemt met de plantgevoeligheidskromme van 35 jaar geleden; gemeten aan rassen van toen, maar nog steeds in gebruik
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