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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Gridded Hourly Temperature, Radiation and Makkink Potential Evaporation forcing for hydrological modelling in the Rhine basin
Osnabrugge, B. van; Weerts, A.H. - \ 2018
climatology - forcing - hydrological modelling - Makkink potential evaporation - radiation - Rhine basin - temperature
Hourly gridded observation based estimates for energy related meteorological forcing variables for a gridded hydrological model of the Rhine basin: temperature, radiation and makkink potential evaporation.
Woningbouw en hittestress in een veranderend klimaat : testbed Den Haag
Koopmans, S. ; Ronda, R.J. ; Steeneveld, G.J. - \ 2018
De Bilt : KNMI (KNMI Intern Rapport IR-2018-03) - 28 p.
heat stress - climate - plantations - temperature - urban areas
Aanleiding voor deze studie is de beleidsopgave van Nederland om tot 2040 nog één miljoen additionele woningen te bouwen (EIB, 2015), waarvan naar verwachting een groot deel zal worden toegevoegd aan de huidige woningvoorraad van de grootste steden in Nederland. De reden hiervoor is dat er ook in Nederland een trek naar de stad gaande (CBS, 2016) is, waarbij naar verwachting de bevolking in de grootste Nederlandse gemeenten sterk toeneemt, terwijl de bevolking in kleine, perifeer gelegen gemeenten juist krimpt. Deze beleidsopgave betekent dat de druk op de bebouwde omgeving steeds meer zal toenemen en heeft onder meer tot gevolg dat steeds meer mensen zullen worden blootgesteld aan het specifieke lokale klimaat in de stad (zie box 1), een uitdaging die steeds urgenter wordt als door een, veranderend klimaat de temperatuur in zowel het rurale gebied als in de stad verder toeneemt.
Physiological responses of rice to increased day and night temperatures
Shi, Wanju - \ 2017
University. Promotor(en): Paul Struik, co-promotor(en): Xinyou Yin. - Wageningen : Wageningen University - ISBN 9789463437110 - 202
crops - rice - oryza sativa - plant physiology - temperature - crop yield - grain - agronomy - gewassen - rijst - plantenfysiologie - temperatuur - gewasopbrengst - graan - agronomie

A more rapid increase in night-time temperature compared with day-time temperature and the increased frequency of heat waves associated with climate change present a serious threat to rice (Oryza sativa L.) production and food security. This thesis aims to understand the impact of high night-time temperature (HNT) and high day-time temperature (HDT) on rice grain yield and grain quality and to examine adaptation strategies to cope with high-temperature stresses.

Grain yield and quality of a susceptible indica genotype (Gharib) and all tested hybrids, when exposed to HNT in the field, were significantly reduced across seasons, with less average reduction in the dry season than in the wet season, indicating that other environmental factors under field conditions may contribute to impacts of HNT on yield. Among the different yield components, a reduced number of spikelets m−2 significantly contributed to yield loss under HNT followed by the consistently lower single-grain weight across all genotypes, while the impact of the decrease in percentage seed-set was less and season-specific. Lower grain yield and poorer grain quality in susceptible cultivar Gharib were associated with a significant reduction in non-structural carbohydrate translocation after flowering, resulting in reduced grain-filling duration. Increased total nitrogen application did not alleviate the negative impact of HNT. The proposed model approach showed that there were significant differences among cultivars in their changes in source-sink relationships in response to HNT. Given that rice grain yield and quality are challenged by a rise in HDT and HNT, in particular at flowering and during grain filling, differential impacts of HNT and HDT during these critical stages were observed. For the single-grain growth during grain filling, HDT either independently or in combination with HNT exerted greater influences than HNT on the grain filling dynamics, activities of starch metabolism enzymes, temporal starch accumulation patterns, and the process of chalk formation. During flowering, HDT increased spikelet sterility in tested hybrids and hybrids were less tolerant to high temperatures than high-yielding inbred varieties. Moreover, in contrast with HNT, HDT played a dominant role in determining spikelet fertility. Novel observations with a series of snapshots of dynamic fertilization processes demonstrated that disturbances in the pre-fertilization phase were the primary causes for heat-induced spikelet sterility, indicating the effectiveness of employing the early-morning flowering trait for mitigating the impact of heat stress at flowering on rice.

A floor cover to improve temperature distribution and quality preservation in maritime refrigerated container transport of grapes : GreenCHAINge WP1 - Table Grapes
Lukasse, Leo ; Mensink, Manon ; Wissink, Edo - \ 2017
Wageningen : Wageningen Food & Biobased Research (Wageningen Food & Biobased Research report 1733) - ISBN 9789463436601 - 32
refrigerated transport - containers - sea transport - grapes - covers - temperature - food quality - koeltransport - zeetransport - druiven - bedekkingsmaterialen - temperatuur - voedselkwaliteit
Like many other fruits, table grapes depend on accurate temperature management during transport in maritime refrigerated containers. Ideally the temperature inside the container is equal to set point in every location in the container. Unfortunately door-end temperatures are always higher due to poor air flow distribution. In climate chamber tests Lukasse & Staal (2016a and 2016b) investigated the effect of covering sections of the container’s T-bar floor. The best T-bar floor cover found in that study was a trapezoid-shape floor cover. The aim of this study is to assess the effect of that trapezoid-shape T-bar floor cover on temperature and fruit quality in commercial reefer container transports of grapes. A field experiment was done in a commercial container shipment of six standard 40 ft. HC reefer containers travelling from South Africa to The Netherlands taking 24 days. The three test containers contained a T-bar floor cover. The three reference containers did not contain the T-bar floor cover. All other parameters were, to the extent possible, the same for all containers. In 31 locations air temperature between the fruit was logged at an interval of 10 min. with an accuracy of approx. ± 0.1 °C. 15 Trays, evenly distributed in a vertical plane on the container’s longitudinal centre line, were weighed at origin and at destination. At destination the fruit quality of these 15 trays was analysed. A clear positive effect on temperature was observed. The floor cover reduces the average difference between warmest and coldest temperature in the trays by approx. 30%. An effect on grape quality could not be assessed.
Hemp (Cannabis sativa L.) leaf photosynthesis in relation to nitrogen content and temperature : implications for hemp as a bio-economically sustainable crop
Tang, Kailei ; Struik, Paul C. ; Amaducci, Stefano ; Stomph, Tjeerd Jan ; Yin, Xinyou - \ 2017
Global change biology Bioenergy 9 (2017)10. - ISSN 1757-1693 - p. 1573 - 1587.
Hemp (Cannabis sativa L.) - model - nitrogen - photosynthesis - sustainable crop - temperature

Hemp (Cannabis sativa L.) may be a suitable crop for the bio-economy as it requires low inputs while producing a high and valuable biomass yield. With the aim of understanding the physiological basis of hemp's high resource-use efficiency and yield potential, photosynthesis was analysed on leaves exposed to a range of nitrogen and temperature levels. Light-saturated net photosynthesis rate (Amax) increased with an increase in leaf nitrogen up to 31.2 ± 1.9 μmol m−2 s−1 at 25 °C. The Amax initially increased with an increase in leaf temperature (TL), levelled off at 25–35 °C and decreased when TL became higher than 35 °C. Based on a C3 leaf photosynthesis model, we estimated mesophyll conductance (gm), efficiency of converting incident irradiance into linear electron transport under limiting light (κ2 LL), linear electron transport capacity (Jmax), Rubisco carboxylation capacity (Vcmax), triose phosphate utilization capacity (Tp) and day respiration (Rd), using data obtained from gas exchange and chlorophyll fluorescence measurements at different leaf positions and various levels of incident irradiance, CO2 and O2. The effects of leaf nitrogen and temperature on photosynthesis parameters were consistent at different leaf positions and among different growth environments except for κ2 LL, which was higher for plants grown in the glasshouse than for those grown outdoors. Model analysis showed that compared with cotton and kenaf, hemp has higher photosynthetic capacity when leaf nitrogen is <2.0 g N m−2. The high photosynthetic capacity measured in this study, especially at low nitrogen level, provides additional evidence that hemp can be grown as a sustainable bioenergy crop over a wide range of climatic and agronomic conditions.

Metropolitan solutions: Droge voeten in een groene stad
Hattum, T. van - \ 2017
Wageningen : Wageningen University & Research
klimaat - hittetolerantie - stedelijke gebieden - luchtkwaliteit - regenwateropvang - temperatuur - climate - heat tolerance - urban areas - air quality - water harvesting - temperature
Door klimaatverandering krijgen we steeds vaker te maken met hevige regenval en periodes van extreme hitte en droogte. Veel steden zijn hier niet tegen opgewassen en moeten anders ingericht gaan worden. Groene oplossingen kunnen wateroverlast beperken, de temperatuur verlagen en de luchtkwaliteit verbeteren. Tim van Hattum van Wageningen University & Research vertelt er alles over.
Gezondheidseffecten onder de loep : weldadig groen
Spijker, J.H. ; Vries, S. de - \ 2017
Stadswerk (2017)6. - ISSN 0927-7641 - p. 34 - 36.
gezondheid - warmtestress - temperatuur - kwaliteit - beplantingen - biodiversiteit - stedelijke gebieden - bevolking - stressfactoren - sociaal welzijn - klimaat - health - heat stress - temperature - quality - plantations - biodiversity - urban areas - human population - stress factors - social welfare - climate
Groen speelt een sleutelrol bij een gezonde leefomgeving. De gezondheidseffecten spelen op diverse manieren, maar vooral door de stressverlagende effecten van groen en de hittedempende werking op warme dagen. Het is daarbij wel belangrijk om niet alleen naar de kwantiteit maar ook naar de kwaliteit van het groen te kijken.
Greenery and residential : a summary of the positive effects of greenery on well-being in residential
Hiemstra, J.A. ; Vries, S. de; Spijker, J.H. - \ 2017
Wageningen University & Research - 7 p.
residential areas - housing - plantations - public green areas - gardens - domestic gardens - health indicators - green roofs - green walls - temperature - climate - heat stress - health - woonwijken - huisvesting - beplantingen - openbaar groen - tuinen - tuinen bij het huis - gezondheidsindicatoren - groene daken - groene gevels - temperatuur - klimaat - warmtestress - gezondheid
Greenery and residential : a summary of the positive effects of greenery on well-being in residential
Nocturnal parasitism of moth eggs by Trichogramma wasps
Woelke, Joop ; Bukovinszki, Tibor ; Huigens, M.E. - \ 2017
Biocontrol Science and Technology 27 (2017)6. - ISSN 0958-3157 - p. 769 - 780.
Circadian rhythm - egg parasitoid - Ephestia kuehniella - offspring production - scotophase - temperature
Parasitoid wasps of the genus Trichogramma are used worldwide as biological control agents against lepidopteran pests. Trichogramma wasps develop inside eggs of a wide range of host species, most of them moths. They are generally considered as diurnal insects. Here, we investigated whether Trichogramma wasps can also successfully parasitise host eggs at night under controlled laboratory conditions. Eggs of the moth Ephestia kuehniella were offered under dark conditions (scotophase) to females of Trichogramma brassicae and Trichogramma evanescens either from 9:00 PM to 9:00 AM or from 11:00 AM to 5:00 PM at four different temperatures (5°C, 10°C, 15°C and 20°C). Both species are known to parasitise E. kuehniella eggs in the photophase during daytime. The results show that T. brassicae did not parasitise eggs in the scotophase at night and only very few in the artificially induced scotophase during daytime from 10°C to 20°C. In contrast, T. evanescens parasitised more eggs in the dark both at night and artificially induced scotophase during daytime. Parasitism in the scotophase already started at 5°C, with more eggs being parasitised and more offspring being produced at higher temperatures. T. evanescens displayed higher parasitism activity in the induced scotophase during daytime than in the scotophase at night. The present study suggests that Trichogramma are capable of successfully parasitising host eggs at night, even at low temperatures, but that nocturnal activity with respect to parasitism varies between wasp species.
Crop growth and development in closed and semi-closed greenhouses
Qian, Tian - \ 2017
University. Promotor(en): Leo Marcelis, co-promotor(en): Anja Dieleman; Anne Elings. - Wageningen : Wageningen University - ISBN 9789463430708 - 112
crops - crop production - growth - greenhouse crops - greenhouse horticulture - climate - semi-closed greenhouses - photosynthesis - temperature - gewassen - gewasproductie - groei - kasgewassen - glastuinbouw - klimaat - semi-gesloten kassen - fotosynthese - temperatuur

(Semi-)closed greenhouses have been developed over the last decades to conserve energy. In a closed greenhouse, window ventilation is fully replaced by mechanical cooling while solar heat is temporarily stored in an aquifer. A semi-closed greenhouse has a smaller cooling capacity than a closed greenhouse and, in which mechanical cooling is combined with window ventilation. (Semi-)closed greenhouses create new climate conditions: high CO2 concentrations irrespective of the outdoor climate, and vertical gradients in temperature and vapour pressure deficit throughout the canopy. This thesis focuses on the crop physiology in (semi-)closed greenhouses, and investigates the effects of the new climate conditions on crop growth, development and underlying processes.

Cumulative production in (semi) closed greenhouses increased by 6-14% compared to the open greenhouse, depending on the cooling capacity. The production increase in the (semi-)closed greenhouses was explained by the higher CO2 concentrations. In many species, feedback inhibition of photosynthesis occurs when plants are grown at high CO2. The results, however, suggest that high CO2 concentrations do not cause feedback inhibition in high producing crops, because the plants have sufficient sink organs (fruits) to utilise all assimilates. Pruning experiments showed that photosynthetic acclimation to elevated CO2 concentration only occurred when the number of fruits was considerably reduced.

Cooling below the canopy induced vertical temperature and vapour pressure deficit gradients. These gradients correlated with outside radiation and outside temperature. Despite the occurrence of vertical temperature gradients, plant growth and fruit yield were mostly unaffected. Leaf and truss initiation rates did not differ in the presence or absence of a vertical temperature gradients, since air temperatures at the top of the canopy were kept comparable. The only observed response of plants to the vertical temperature gradient was the reduced rate of fruit development in the lower part of the canopy. This resulted in a longer period between anthesis and fruit harvest and an increase in the average fruit weight in summer. However, total fruit production over the whole season was not affected.

The effects of the climate factors light, CO2 concentration, temperature, and humidity on leaf photosynthesis were investigated. The photosynthesis model of Farquhar, von Caemmerer and Berry (FvCB) was modified by adding a sub-model for Ribulose-1,5-bisphosphate carboxylase (Rubisco) activation. The photosynthetic parameters: the maximum carboxylation capacity (Vcmax) and the maximum electron transport rate (Jmax), α (the efficiency of light energy conversion), θ (the curvature of light response of electron transport), and Rd (the non-photorespiratory CO2 release) were estimated based on measurements under a wide range of environmental conditions in the semi-closed greenhouse. The simultaneous estimation method and the nonlinear mixed effects model were applied to ensure the accuracy of the parameter estimation. Observations and predictions matched well (R2=0.94).

The yield increase in a closed greenhouse, compared to that in an open greenhouse was analyzed based on physiological and developmental processes. The yield increase in the (semi-)closed greenhouses was the result of an increase of net leaf photosynthesis. The (semi-)closed greenhouses have been applied commercially first in the Netherlands, and later in other countries. The knowledge obtained from (semi-)closed greenhouses is applied in conventional open greenhouse as well, which is called the next generation greenhouse cultivation. A number of innovations are being developed for greenhouse industry to reduce energy consumption while improving production and quality.

Groen en wonen : de meerwaarde van groen voor het welbevinden in de woonomgeving samengevat
Spijker, J.H. - \ 2017
- 7 p.
woonwijken - huisvesting - beplantingen - openbaar groen - tuinen - tuinen bij het huis - gezondheidsindicatoren - culturele waarden - hoveniers - groene daken - groene gevels - temperatuur - plaatsbepaling van bomen - klimaat - warmtestress - welzijn - residential areas - housing - plantations - public green areas - gardens - domestic gardens - health indicators - cultural values - landscape gardeners - green roofs - green walls - temperature - tree orientation - climate - heat stress - well-being
Groen in en rondom woonhuizen en appartementen is goed voor het (leef)klimaat binnen en buiten de woning. Het heeft een positief effect op de gezondheid en het algehele welbevinden van bewoners en bezoekers en verhoogt de waarde van het vastgoed. Dit document biedt meer inzicht in de voordelen van groen in relatie tot wonen en welbevinden, inclusief verwijzingen naar de wetenschappelijke onderbouwing. Het document sluit af met tips die helpen om groen succesvol en volwaardig toe te passen
Groen en herstellen : de meerwaarde van groen voor het welbevinden in de herstelomgeving samengevat
Spijker, J.H. - \ 2017
- 6 p.
welzijn - gezondheid - gezondheidsindicatoren - tuinen - warmtestress - klimaat - temperatuur - luchtkwaliteit - stress - sociaal welzijn - participatie - beplantingen - herstellen - well-being - health - health indicators - gardens - heat stress - climate - temperature - air quality - social welfare - participation - plantations - reconditioning
Groen in en rondom verzorgingshuizen, ziekenhuizen en overige klinieken is goed voor het klimaat binnen en buiten de instelling en heeft een positief effect op het herstellend vermogen en de gemoedstoestand van patiënten, en het algehele welbevinden van patiënten, medewerkers en bezoekers. Dit document biedt meer inzicht in de voordelen van groen in relatie tot herstellen en welbevinden, inclusief verwijzingen naar de wetenschappelijke onderbouwing. Het document sluit af met tips die helpen om groen succesvol en volwaardig toe te passen.
Groen en leren : de meerwaarde van groen voor het welbevinden in de leeromgeving samengevat
Spijker, J.H. - \ 2017
- 7 p.
beplantingen - onderwijs - leren - schoolterrein - leerprestaties - openbaar groen - klimaat - temperatuur - gezondheid - sociaal welzijn - luchtkwaliteit - lichamelijke activiteit - lichamelijke fitheid - stressfactoren - kinderen - plantations - education - learning - school site - educational performance - public green areas - climate - temperature - health - social welfare - air quality - physical activity - physical fitness - stress factors - children
de meerwaarde van groen voor het welbevinden in de leeromgeving samengevat
Temperature in water and sediment in the pesticide model TOXSWA : implementation report
Beltman, W.H.J. ; Adriaanse, P.I. ; Jacobs, C.M.J. ; Mulder, H.M. - \ 2017
Wageningen : Wageningen Environmental Research (Wageningen Environmental Research report 2794) - 67
pesticides - water - temperature - models - sediment - surface water - pesticiden - temperatuur - modellen - oppervlaktewater
TOXSWA simuleert het gedrag van stoffen in oppervlaktewater om blootstellingsconcentratie te berekenen voor organismen die in water of sediment leven, als onderdeel van de aquatische risicobeoordeling van gewasbeschermingsmiddelen (GBM). Het vernieuwde concept voor de beschrijving van de temperatuur in het TOXSWA model werd getest aan de hand van een bestaande implementatie van het 1D bulk model.
The hot, the cold and the tulip : the regulation of flowering time and dormancy release
Leeggangers, Hendrika A.C.F. - \ 2017
University. Promotor(en): Richard Immink, co-promotor(en): Henk Hilhorst. - Wageningen : Wageningen University - ISBN 9789463430289 - 244
tulipa - lilium - tulips - flowering date - flowering - dormancy - plant development - temperature - plant physiology - vegetative propagation - tulpen - bloeidatum - bloei - slaaptoestand - plantenontwikkeling - temperatuur - plantenfysiologie - vegetatieve vermeerdering

The ornamental geophyte Tulipa gesneriana is the most cultivated bulbous species in the Netherlands. It is widely grown in the field for vegetative propagation purposes and in greenhouses for the production of high quality cut flowers. Over the last decade, the tulip bulb industry is affected by the rapid climate change the world is facing. Temperature is rising and influences the vegetative to reproductive phase change (floral induction) inside the tulip bulbs in spring and processes that are occurring during winter, such as dormancy release.

In this thesis the two temperature-dependent processes related to tulip flowering, being floral induction and dormancy release, were investigated in detail with a special focus at the molecular level. Flowering time has been studied in a broad range of species, including the model species Arabidopsis thaliana and Oryza sativa. The current understanding of this process can be translated to non-model species, such as tulip, through a ‘bottom-up’ and ‘top-down’ approach (Chapter 2). For the ‘bottom-up’ approach conservation of molecular pathways is assumed and researchers make use of sequence homology searches to identify candidate genes. The ‘top-down’ approach starts from large scale data mining, such as RNA-sequencing (RNA-seq) data or microarrays, followed by the association between phenotypes, genes and gene expression patterns. Here, a comparison with data from model plant species is made at the end of the process and this also leads to the identification of candidate genes for a particular process.

Large scale genomics data mining in tulip is only possible via transcriptome analysis with RNA-seq derived data, because no full genome-sequence is present at this moment. Genome sequencing remains a challenge for species with a large and complex genome, containing probably a large number of repetitive sequences, which is the case for tulip and lily. In chapter 3 a high quality transcriptome of tulip and lily is presented, which is derived from a collection of different tissues. In order to obtain good transcriptome coverage and to facilitate effective data mining, different filtering parameters were used. This analysis revealed the limitations of commonly applied methods used in de novo transcriptome assembly. The generated transcriptome for tulip and lily is made publicly available via a user friendly database, named the ‘Transcriptome Browser’.

The molecular regulation of the temperature-dependent floral induction was studied through the use of RNA-seq (Chapter 4). A better understanding of this process is needed to prevent floral bud blasting (dehydration of the flower) in the future. The development at the shoot apical meristem (SAM) was morphologically investigated in two contrasting temperature environments, high and low. Meristem-enriched tissues were collected before and during the start of flower development. The start of flower development is morphologically visible by rounding of the SAM and correlates with the up-regulation of TGSQA, an AP1-like gene. A ‘top-down’ approach was used to identify possible regulators of the floral induction in tulip. However, Gene ontology (GO)-enrichment analysis of the differentially expressed genes showed that the floral induction, maturation of the bulb and dormancy establishment are occurring around the same period in time. Therefore a ‘bottom-up’ approach was followed to identify specific flowering time regulators based on knowledge obtained from other species. Expression analysis in tulip, heterologous analysis in Arabidopsis and yeast two hybrid-based protein-protein interaction studies revealed that Tulipa gesneriana TERMINAL FLOWER 1 (TgTFL1) is likely a repressor of flowering, whereas Tulipa gesneriana SUPPRESSOR OF OVEREXPRESSION OF CONSTANS-LIKE2 (TgSOC1L2) acts probably as a floral activator.

Another well-known flowering time regulator is FLOWERING LOCUS T (FT), which is a member of the PEBP gene family found in Arabidopsis and many more plant species. In tulip and lily, a total of four highly similar sequences to FT and HEADING DATA 3A (Hd3a) were identified (Chapter 5). Overexpression of Lilium longiflorum FT (LlFT) and TgFT2 in Arabidopsis resulted in an early flowering phenotype, but upon overexpression of TgFT1 and TgFT3 a late flowering phenotype was observed. The tulip PEBP genes TgFT2 and TgFT3 have a similar expression pattern during development, but show a different behaviour in Arabidopsis. Therefore the difference within the amino acid sequence was investigated, which resulted in the identification of two important amino acids for the FT function, which appeared to be mutated in TgFT3. Interchanging of these amino acids between TgFT2 and TgFT3 resulted in conversion of the phenotype, showing the potential importance of these positions in the protein and these specific amino acids for the molecular mode of action of these two proteins. Based on all the data, LlFT is considered to play a role in creating meristem competency to flowering related cues and TgFT2 to act as a florigen involved in the floral induction. The function of TgFT3 is not clear, but phylogenetic analysis suggests a bulb specific function.

After the floral induction and completion of flower development inside the tulip bulb, a period of prolonged cold is required for proper flowering in spring. Low temperature stimulates the re-mobilization of carbohydrates from the scale tissues to the sink organs, such as the floral stem, floral bud and leaves. Not many details are known about the molecular and metabolic changes during this cold period. In chapter 6, first insights are shown on the development of the different tissues inside the bulbs. The floral bud appears to be the least active tissue in comparison with the floral stem and leaves, suggesting a type of floral bud dormancy in tulip. However, metabolic changes are suggesting that the floral bud is still showing active cell division and/or preparation for elongation by turgor-driven cell wall extension. Dormancy of all tissues seems to be released ten weeks after planting and is correlated with the increase of glucose levels. In the leaves, from this same moment, photosynthesis related genes are up-regulated suggesting that the leaves are preparing for photosynthesis while still beneath the soil surface.

At the end of the thesis a glance is given at different perspectives of the tulips life cycle, categorizing tulip as a perennial, biennial or annual plant species, respectively. The perennial way of life is applicable when growing bulbs from seeds, while biennial and annual are more in relation to vegetative propagation. Also the importance of bulb size is highlighted, because it will determine if the bulbs are able to flower or not the following spring. Two scenarios are discussed related to availability of energy in the presence of carbohydrates and meristem incompetency to floral inducing signals. Throughout all research done for this thesis, it became clear that tulip bulbs and seeds have a lot in common. By combining the knowledge of processes in different plant species or developmental systems it is possible to understand how flowering and dormancy release are regulated and this provides us with novel insights how these processes are regulated in bulbous plant species, such as tulip.

Koudetolerantie Phalaenopsis : GreenCHAINge onderzoek potplanten 2016
Harkema, Harmannus ; Hogeveen, Esther ; Otma, Els ; Leentfaar, Gerard - \ 2017
Wageningen : Wageningen Food & Biobased Research (Wageningen Food &amp; Biobased Research rapport 1698) - ISBN 9789463430593 - 48
koudebeschadiging - potplanten - orchideeën als sierplanten - koudeopslag - temperatuur - gevoeligheidsanalyse - chilling injury - pot plants - ornamental orchids - cold storage - temperature - sensitivity analysis
Ambient temperature‐directed flowering time regulation : the role of alternative splicing
Verhage, Dina Sara Leonie - \ 2017
University. Promotor(en): Gerco Angenent, co-promotor(en): Richard Immink; Guusje Bonnema. - Wageningen : Wageningen University - ISBN 9789462579705 - 161
plants - flowering date - flowering - temperature - alternative splicing - molecular biology - genes - planten - bloeidatum - bloei - temperatuur - alternatieve splitsing - moleculaire biologie - genen

As a consequence of a sessile lifestyle, plants are constantly facing a fluctuating environment. In order to both profit maximally and protect themselves from these environmental cues, plants evolved ways to sense and respond to signals.

Ambient temperature is one of the cues for which plants have acquired a strategy to enhance their chance of survival and reproduction. Small changes in ambient temperature can have major effects on plant architecture and development, such as the transition from the vegetative to the reproductive flowering phase. The moment of flowering is an important event in the life cycle of a plant, since reproductive success depends on it.

In Chapter 1, I introduced the concept of alternative splicing, a molecular mechanism with a pivotal role in ambient temperature regulation of flowering time. In the model plant Arabidopsis thaliana, approximately 60% of the intron-containing genes show alternative splicing. Gene splicing varies depending on developmental stage and tissue type, but also environmental changes trigger differential splicing. Splicing is conducted by a large cellular machinery called the spliceosome, which recognizes intron-defining sequences and other cis-regulatory elements acting as splicing enhancers or silencers. Moreover, factors like chromatin structure, histone marks, RNA polymerase II (polII) elongation speed and the secondary structure of the pre-mRNA all play a role in the splicing outcome. Due to alternative splicing, a single gene can yield various transcripts. However, this does not cause an equal expansion of the proteome. Part of the transcripts are targeted for nonsense-mediated decay, or will be translated into unstable proteins. This is a way of regulating gene expression at the post-transcriptional or –translational level. Other transcripts will be translated into functional proteins that may be structurally and functionally different. Hence, alternative splicing creates additional complexity in the transcriptome, providing plants with molecular tools to respond to their environment, including the translation of ambient temperature alterations into a flowering time response.
In Chapter 2, we reviewed the current knowledge on molecular mechanisms that control the ambient-temperature directed flowering time pathway in the plant model species Arabidopsis thaliana. Several different mechanisms have been proposed, like alternative splicing of FLOWERING LOCUS M (FLM) (described in Chapter 4) and protein degradation of SHORT VEGETATIVE PHASE (SVP), two mechanisms that probably work in a cooperative manner to release floral repression at higher ambient temperatures. Another mechanism that is involved at high ambient temperature is the replacement of the canonical histone H2A by the variant H2A.Z. As a consequence of this replacement, chromatin becomes less tightly wrapped around the nucleosomes, which allows transcription of flowering time activators, such as PHYTOCHROME INTERACTING FACTOR 4 (PIF4). Lastly, we discuss microRNAs (miRNA) that can either repress or activate flowering (miR156 and miR172, respectively). These miRNAs have been proposed to be regulated by low and high ambient temperature. However, due to the lack of mutant analyses, more research is necessary to show the true involvement of these factors. Altogether, there are several mechanisms acting partly in cooperation to regulate thermosensitive floral timing.
In Chapter 3, we analysed ambient temperature-directed alternative splicing events that occur after a temperature shift by RNAseq. We performed the experiment in two different accessions of A. thaliana, and in one variant of B. oleracea (cauliflower). We showed that flowering time genes are overrepresented amongst the ambient temperature induced alternatively spliced genes, but also genes encoding components of the splicing machinery itself, indicating that alternative splicing is one of the potential mechanisms by which plants are able to sense temperature and adapt floral timing. Analysis of a mutant for one of these alternatively-spliced splicing related factors, ATU2AF65A, showed a temperature-dependent flowering time phenotype, confirming its proposed role in the flowering time response upon temperature fluctuations. Based on these findings, we proposed a two-step model in which splicing related genes are targeted for differential splicing upon ambient temperature fluctuations, which results in changes in the composition of the spliceosome, causing differential splicing of downstream genes that affect the development and architecture of the plant, including flowering time.
In Chapter 4, we investigated the molecular mode-of-action of FLM, one of the differentially spliced flowering time regulating genes that we identified in Chapter 3. We showed that in A. thaliana Col-0, the main splice forms of FLM are FLMβ and FLMδ. FLMβ forms an obligate heterodimer with SVP, and this complex represses floral integrators like SUPPRESSOR OF OVEREXPRESSION OF CONSTANS1 (SOC1) by binding to the regulatory regions of these genes. FLMδ also dimerizes with SVP, but this complex is not able to bind to DNA. When temperature rises, more FLMδ is produced at the cost of FLMβ. Hence, less repressive complexes can be formed. However, the fact that FLMδ is still able to binds SVP makes it function as a dominant negative form, titrating out SVP and preventing repressive SVP/FLMβ-complex formation.
Chapter 5 is a short comment written to clarify the concept of thermoplasticity in flowering time control. Occasionally, this concept is confused with adaptation to different ambient temperature environments on the long term. Thermoplasticity is the ability to adapt flowering time to fluctuations in ambient temperature within one life cycle. Furthermore, some genes have been marked as players in the ambient temperature response, whereas these appear to be general flowering repressors or activators, affecting flowering time in a similar manner at low and high ambient temperature. In order to interpret novel findings on thermosensitive flowering time control, it is essential to distinguish between these various concepts.
In chapter 6, we unveiled the first indications that differential splicing of FLM can be caused by differences in polymerase II elongation rate. We mimicked a situation in which FLM is transcribed at a higher rate, by expressing the genomic FLM gene under a strong artificial promoter. Preliminary results showed that plants harbouring this construct have altered flowering time and temperature-responsiveness, which can be explained by the altered FLMβ/FLMδ ratio that we observed.
In chapter 7, we assessed the functional conservation between FLM and closely related genes at the intraspecific level in A. thaliana. FLM (also called MAF1) is a member of the FLC-clade, that consists of FLC, FLM and MAF2-5. FLC is widely known for its function in the vernalization pathway, whereas MAF2 has been shown to regulate flowering time through alternative splicing in a way very similar to FLM. For the other MAF genes, not much is known. We showed that all of these genes produce splicing isoforms that function in a more or less similar way to FLM and MAF2. Despite the high functional conservation at the intraspecific level, FLM and MAF orthologues are not widely present. Through synteny analysis, we showed that FLM and MAF2 are very recent genes, which are only present in a small group of Brassicaceae species. MAF3-5 originated less recently, but are not present outside the Brassicaceae. For FLC, it was previously shown that it originated from an ancestor of the seed plants, and in many plant species belonging to other families, presence of more than one FLC-like gene has been reported. This raises the question what the function of these genes is. In tomato, we showed that the FLC-like gene MBP8 becomes differentially spliced upon temperature changes, suggesting a function in the ambient temperature pathway. A binding assay showed high similarities of the different MBP8 isoforms to FLM and MAF isoforms, but suggests a slightly different functionality, since all three isoforms showed binding to the DNA. Further research is necessary to confirm the role of MBP8 in thermosensitive flowering time control, and elucidate the functionality of the different splice forms.
In Chapter 8, I discussed the finding of this thesis in a broader perspective, and make suggestions for future research. Over the last few years, several mechanisms that act in the temperature-directed floral pathway have been revealed. In this thesis, we showed that alternative splicing plays an important role, and we demonstrated how temperature may affect the splicing outcome directly through the effect of temperature on transcription elongation rate. It is becoming clear that most likely a single thermosensor does not exist in plants, and a model in which temperature is sensed through thermodynamic properties of DNA, RNA and proteins, is gaining support. Future research is assigned to the exiting task to elucidate the exact mechanisms by which temperature-sensing is achieved in different plant species and to determine how conserved the currently identified molecular mechanisms are.

Temperature during the last week of incubation. III. Effects on chicken embryo physiology
Maatjens, C.M. ; Roovert-Reijrink, I.A.M. van; Engel, B. ; Pol, C.W. van der; Kemp, B. ; Brand, H. van den - \ 2017
Poultry Science 96 (2017)5. - ISSN 0032-5791 - p. 1451 - 1458.
temperature - incubation - chicken embryo physiology - hepatic glycogen
We investigated effects of eggshell temperature (EST) of 35.6, 36.7, 37.8, or 38.9°C applied from d of incubation (E) 15, E17, or E19 onward on chicken embryo physiology. A total of 2,850 first-grade eggs of a 43-week-old Ross 308 broiler breeder flock were incubated at an EST of 37.8°C until E15. From E15, E17, or E19 onward, eggs were incubated at an EST of 35.6, 36.7, 37.8, or 38.9°C. Plasma glucose, uric acid, and lactate concentrations, and hepatic glycogen amount and concentration were measured at E15, E17, E19, internal pipping (IP), external pipping (EP), and hatch.
An EST of 38.9°C applied from E15 onward decreased the amount of hepatic glycogen from E19 to IP and resulted in a lower glycogen amount at IP compared to all other EST. At EP, when oxygen (O2) becomes largely available, an EST of 38.9°C resulted in a higher glycogen amount and concentration compared to IP, which suggests that plasma glucose between IP and EP might be used for building up hepatic glycogen reserves. However, hepatic glycogen levels remained considerably lower at IP, EP, and hatch at an EST of 38.9°C, compared to an EST of 35.6 and 36.7°C.
Opposite to an EST of 38.9°C, from IP onward, an EST of 35.6°C resulted in a higher glycogen amount and concentration compared to all other EST, which might be caused by the higher O2 availability relative to the lower metabolic rate, which provided time to build up glycogen stores from excessive glucose. A higher availability of hepatic glycogen might contribute to an improved physiological status of the broiler chicken embryo toward hatch. Hepatic gluconeogenesis is crucial for developing embryos, as glucose is the major energy source from IP until hatch. At hatch, no effect of EST was found for glucose, uric acid, or lactate.
Results of this study emphasize that EST of 35.6 and 36.7°C from E15 onward appear to be beneficial for chicken embryo physiology.
Plant reageert bij bloei op externe signalen als temperatuur en daglengte : vernalisatie zorgt voor het juiste bloeitijdstip
Heuvelink, E. ; Kierkels, T. - \ 2016
Onder Glas 13 (2016)12. - p. 40 - 41.
temperatuur - fotoperiode - planten - bloei - milieufactoren - temperature - photoperiod - plants - flowering - environmental factors
Een plant die op het punt staat te gaan bloeien, kan zich niet bedenken als de omstandigheden toch tegen blijken te vallen. De overgang naar de bloei is onomkeerbaar. Daarom is het van het grootste belang voor het voortbestaan van de soort dat de bloei precies op het juiste tijdstip valt. Om dat voor elkaar te krijgen, reageert de plant op externe signalen, vooral de temperatuur en de daglengte.
Stress speelt een belangrijke rol : inzicht in koploosheid groeit door gezamenlijk onderzoek
Groot, S.P.C. ; Kierkels, T. ; Heuvelink, E. - \ 2016
Onder Glas 13 (2016)8. - p. 30 - 31.
tuinbouw - groenten - landbouwkundig onderzoek - groeistoornis - plantenontwikkeling - verlichting - tomaten - capsicum - brassica - gypsophila - stresstolerantie - temperatuur - horticulture - vegetables - agricultural research - failure to thrive - plant development - lighting - tomatoes - stress tolerance - temperature

Jonge tomaten- en paprikaplanten, maar ook een aantal andere gewassen, houden soms opeens op met groeien. Koploosheid was lange tijd een lastig maar zeer slecht begrepen fenomeen. De laatste jaren is het inzicht in een stroomversnelling gekomen. In ieder geval is het aantal mogelijke oorzaken drastisch ingeperkt.
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