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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    Light on phloem transport (an MRI approach)
    Prusova, Alena - \ 2016
    Wageningen University. Promotor(en): Herbert van Amerongen, co-promotor(en): Henk van As. - Wageningen : Wageningen University - ISBN 9789462579156 - 130
    solanum lycopersicum - phloem - light - flow - photoperiod - nuclear magnetic resonance - biophysics - magnetic resonance imaging - solanum lycopersicum - floëem - licht - stroming - fotoperiode - kernmagnetische resonantie - biofysica - kernspintomografie

    This thesis (Light on phloem transport – an MRI approach) aims to answer the question whether phloem transport can be a limiting factor for photosynthesis efficiency (and ultimately causing a bottleneck towards achieving higher yields). To answer this key question, we manipulated the source: sink ratio within tomato (Solanum lycopersicum L.) while measuring phloem transport with magnetic resonance imaging (MRI) flowmetry. Additionally we compared phloem flow characteristics of two potato plants (Solanum tuberosum L.) which differed in source : sink ratio. In Chapter 2, the source strength was manipulated by varying the light intensity. An increase in phloem sap volume flow under higher light intensities was observed. However, under all light intensities applied, the phloem flow velocity was found to be constant (as has previously been suggested in other studies) although a clear diurnal pattern was observed. This finding does not fit in current models to describe the mechanism of phloem transport and a different mechanism must be at play. The results of this chapter demonstrate that increased levels of photo-assimilates are transported in sieve tubes, which are activated when needed by the plant. This is the first study which shows that plants activate individual sieve tubes when more photo-assimilates are available, yet maintain constant velocity. Those observations were in a tomato plant with pruned fruit trusses (i.e., in a simplified system). In Chapter 3, we investigated whether tomato plants still exhibit constant phloem flow velocity (with a diurnal pattern) under normal conditions, i.e., with strong sinks (tomato fruits) still attached. This was tested for both a long and short photoperiod by measuring flow characteristics with MRI flowmetry. We simultaneously monitored other plant processes like xylem flow rates with a heat balance sensor, net photosynthesis with gas exchange and stem diameter changes with a linear motion potentiometer. With this integrated approach, we revealed a correlation between night phloem volume flow, dark respiration and stem growth. We also conclusively showed that phloem volume flow performs a diurnal pattern under a variety of source-sink ratios which appears to be a normal behaviour for tomato plants growing under moderately-high light conditions. In chapters 2 and 3 we learned that under higher source strength a greater amount of phloem sap is transported, but the changes in flow were not accompanied by changes in velocity. To further our understanding of the mechanisms driving phloem transport, it is of interest to know how the sucrose concentration in phloem sap relates to phloem flow. In Chapter 4 we used an average T2 relaxation time in the phloem vascular tissue region to reveal the plant’s phloem carbon status under source manipulation. In this chapter we demonstrated that T2 relaxation time, when measured in parallel with phloem flow, can provide additional information about phloem region carbon status, i.e., changes in the T2 relaxation time are correlated with changes in sucrose concentration in the whole phloem region.

    When studying phloem transport in plants with magnetic resonance imaging (MRI) flowmetry, plants which are relatively easy to manipulate (e.g. fruit pruning) like tomato have so far been used. However, tomato plants (used in all three previous chapters) have relatively low sink strength beneath the MRI measurement site. A potentially preferable approach is to work with plants with strong sinks beneath the measurement site. In Chapter 5 we studied potato as a potentially better test subject for MRI flowmetry as it possesses strong sink below the MRI measurement site (i.e., developing tubers). For that purpose we used two potato plants (cv. Desiree) both with several developing tubers. One of the plants overexpressed the StSWEET gene (35S:StSWEET) which appears to have altered its source : sink ratio. As a result, the 35S:StSWEET plant transported 60% more phloem sap than Desiree WT. Strikingly, the average phloem flow velocity in both plants was the same and the greater amount of transported phloem sap in the 35S:StSWEET plant was accommodated by more sieve tubes than in Desiree WT. This finding agrees with the hypothesis about the conserved nature of phloem flow velocity, where volume flow is regulated by the number of active sieve tubes (Chapter 2 and 3). In this chapter we also demonstrate that a potato plant with developing tubers represents a good subject to study phloem transport with MRI flowmetry. We concluded that under optimal conditions (which are commonly met in greenhouses) phloem transport is likely to reach its maximum capacity and therefore photosynthesis could be limited by the export and transport of photo-assimilates because of the finite number of sieve tubes and constant flow velocity.

    Nuclear magnetic response imaging of sap flow in plants
    Windt, C.W. - \ 2007
    Wageningen University. Promotor(en): Herbert van Amerongen; T.J. Schaafsma, co-promotor(en): Henk van As. - [S.l.] : S.n. - ISBN 9789085047292 - 172
    sapstroom - kernmagnetische resonantie - transport over water - floëem - ricinus communis - sap flow - nuclear magnetic resonance - water transport - phloem - ricinus communis

    This thesis deals with Nuclear Magnetic Resonance (NMR) imaging of long distance transport in plants. Long distance transport in plants is an enigmatic process. The theoretical framework that describes its basic properties has been in place for almost a century, yet at the same time only little is known about the dynamics of long distance transport inside the living plant. The latter is caused by the fact that the two pathways in which transport takes place, the xylem and the phloem, are virtually inaccessible to invasive experimentation. As a result a wide range of questions about the dynamics of long distance transport have yet to be answered. Examples of such questions, as addressed in this study, are: how fast does phloem sap move; how variable is the phloem sap flow velocity between species and over the diurnal cycle; what percentage of the potential flow conducting area in xylem tissue is functional. Or with regard to fruits: what percentage of the influx to fruits occurs through the xylem, what percentage through the phloem; does the xylem remain functional throughout fruit development; and does backflow from the fruit to the plant occur. Here, we show that NMR flow imaging provides a non-invasive and quantitative means to answer these intriguing questions.
    In order to be able to compare the results from different plants, the flow imaging data need to be independent from anatomical characteristics such as conduit diameter. To quantify flow, the signal from a known quantity of water in a reference object is compared with the signal from flowing water in the plant. When the NMR signals arising from the flowing water in the plant and that of the reference object have different relaxation rates, quantification problems may arise. In porous materials relaxation is influenced by pore diameter. Correspondingly, the relaxation of flowing water in plants will be influenced by conduit diameter. We developed a T2 resolved flow imaging method to measure the T2 relaxation behaviour of the flowing water (chapter 2), and used it to determine how xylem conduit diameter affects T2 relaxation. Furthermore, we investigated whether conduit diameter dependent T2 changes need to be corrected for when quantifying results of NMR flow imaging (chapter 3). We found that conduit diameter indeed affected the T2 of the flowing water. However, because the effects were relatively small, T2 resolved flow imaging was not needed to correct for conduit diameter induced changes in T2. Standard, non flow resolved T2 imaging sufficed. The accuracy of the quantification of volume flow in the xylem in all cases was ±10% or better. The T2 resolved flow imaging sequence that was developed will be of interest for research that deals with liquids moving through microscopic conduits, such as porous media, bioreactors, and biomats.
    With regard to the dynamics and basic properties of xylem and phloem transport, three subjects are taken into account: xylem transport, phloem transport, and long distance transport to fruits.
    For the xylem, one of the questions to be solved is how much of the potential flow conducting area that is present in the xylem anatomy, is in reality used to conduct flow. Xylem tissue consists of many conduits of varying diameters, ranging from small to large. We investigated the relationship between xylem conduit diameter distribution and flow conducting area in stems of various plant species (chapter 3), and the relation between the diurnal dynamics of xylem sap flow and the flow conducting area (chapter 4). We found that in the stems with the widest conduits only a small proportion of the potential flow conducting area conducted flow (as low as 31%). In stems that only possessed narrow conduits, a much larger part of the total xylem conduit cross sectional area conducted flow (up to 86%). We conclude that when wide conduits are present and are functional, the role of the narrowest conduits in terms of the conductance of water is almost negligible. Secondly, we found that the flow conducting area does not stay constant throughout the diurnal cycle. Decreases in xylem flux at night were accompanied by a decrease in velocity, but also by a decrease in flow-conducting area. It is well known that plant stems exhibit a diurnal pattern of shrinkage and expansion due to changes in xylem pressure. However, the diurnal changes in the flow conducting area were opposite to the changes in stem diameter and thus could not be explained by pressure dependent elastic changes in conduit diameter.
    With regard to the phloem we investigated the following questions: how fast does phloem sap move, how variable is the sap flow velocity between species and over the diurnal cycle; and what percentage of the shoot-bound xylem sap is returned to the root system by means of the phloem (chapter 4). Furthermore we investigated how phloem volume flow responds to local cooling (chapter 6). We compared the diurnal phloem and xylem flow dynamics in poplar, tomato, castor bean, and tobacco. In contrast to the highly variable sap flow velocities in the xylem, the sap flow velocities in the phloem remained very constant throughout the diurnal cycle. The differences in the average phloem flow velocity between the four species also were remarkably small (0.25 - 0.40 mm/s). We hypothesize that upper and lower bounds for phloem flow velocity may exist: when phloem flow velocity is too high, wall bound (parietal) organelles may be stripped away from sieve tube walls; when sap flow is too slow or is highly variable, phloem borne signalling could become unpredictable. The phloem to xylem volume flow ratio reflects the amount of xylem water that within the plant is (re)used for phloem transport. It may be indicative for the water use efficiency of a plant. This ratio was surprisingly large at night for poplar, castor bean and tobacco (ranging from 0.19 for poplar to 0.55 in tobacco), but as low as 0.04 in tomato.
    With regard to long distance transport to fruits we investigated three long-standing questions: how much of the influx into the fruit occurs by means of the xylem, and how much by means of the phloem; does the xylem remain functional throughout fruit development; and does backflow from the fruit to the plant occur. As a model system we used a tomato truss. We found that xylem transport into the truss remained functional throughout the full 8 weeks of truss growth. During that period at least 75% of the net influx occurred through the xylem, and about 25% through a region that contains both internal phloem and internal xylem (perimedullary region). These results contradict earlier estimates that were made on the basis of indirect measurements. Halfway during truss development a xylem backflow to the plant appeared. However, the influx volume always was larger, implying that there was no net loss of water from the truss to the plant. Interestingly a circulation of xylem sap in the truss stalk remained even after the fruits were removed, probably caused by pressure gradients originating from the main stem. During the experiment about half of the cumulative net influx into the truss was lost to the air due to evaporation.
    Because of the extreme sensitivity of xylem and phloem to invasive experimentation, only little is known about the dynamics of long distance transport in the living plant. The fact that the exploratory NMR flow imaging experiments in this study swiftly turned up a number of surprises with regard to the dynamics of flow underscores this observation. We found indications that phloem flow velocity is much more constant in nature than previously assumed, over the course of a day as well as between species. We observed that, depending on the species, at night a significant amount of xylem water can be recycled by means of the phloem, thus helping to maintain xylem circulation during periods of low transpiration. With regard to long distance transport to fruits, we found that during truss growth in tomato the majority of water influx does not occur by means of the phloem, but through the xylem. These results illustrate that the dynamics of xylem and phloem sap flow in the living plant are far from being understood, but also that NMR flow imaging provides an excellent non-invasive tool to help elucidate it.

    Stiletpenetratie door bladluizen
    Tjallingii, W.F. - \ 2003
    Entomologische Berichten 63 (2003)5. - ISSN 0013-8827 - p. 110 - 116.
    aphidoidea - voedingsgewoonten - floëem - sapstroom - plantenweefsels - aphidoidea - feeding habits - phloem - sap flow - plant tissues
    Stylet penetration by aphids can be studied well by the electrical penetration graph (EPG) technique, a recording system which incorporates both plant and insect in an electrical circuit. A large number of details of plant-aphid interactions during stylet penetration has been elucidated by EPG-studies
    Tentative determination key to 600 trees, shrubs and climbers from the Ivory Coast, Africa, mainly based on characters of the living bark, besides the rhytidome and the leaf
    Outer, R.W. den - \ 1972
    Wageningen : Veenman (Mededelingen Landbouwhogeschool 72-18,19,20,21) - 4
    planten - identificatie - bedektzadigen - bosbouw - bomen - floëem - schors, bomen - plantenmorfologie - ivoorkust - bladeren - plantenfysiologie - plants - identification - angiosperms - forestry - trees - phloem - bark - plant morphology - cote d'ivoire - leaves - plant physiology
    Movement of 45Ca in the phloem of Yucca
    Wiersum, L.K. ; Vonk, C.A. ; Tammes, P.M.L. - \ 1971
    Wageningen : [s.n.] (Publication / Plant physiological research centre no. 104) - 2
    floëem - liliaceae - yucca - calcium - voedingsstoffen - metabolisme - plantenvoeding - assimilatie - phloem - liliaceae - yucca - calcium - nutrients - metabolism - plant nutrition - assimilation
    Histological investigations of the secondary phloem of gymnosperms
    Outer, R.W. den - \ 1967
    Wageningen University. Promotor(en): A.L. Stoffers. - Wageningen : Veenman - 118
    bosbouw - bomen - naaktzadigen - floëem - cytologie - plantenweefsels - forestry - trees - gymnosperms - phloem - cytology - plant tissues
    An anatomical study of secondary phloem of the different species of Gymnosperms showed that three categories could be distinguished, which may represent three evolutionary stages. These three categories were:

    Pseudotsuga taxifolia type, to which belong many Pinaceae (while the other Pinaceae species belong to a subtype, e.g. the Tsuga canadensis subtype);

    Gingko biloba type, to which belong the Cycadaceae, Araucariaceae and many Podocarpaceae and Taxaceae;

    Chamaecyparis pisifera type, to which belong the Cupressaceae, Taxodiaceae and the rest of the Taxaceae and Podocarpaceae.

    The phylogenetic sequence of the axial system and the reduction of the phloem rays starts in the Ps. taxifolia type with an almost uniform axial system and ray- albuminous cells, and a complex heterogeneous phloem ray, differentiating through the G. biloba type to the C. pisifera type, which has a highly specialized axial system with phloem-albuminous cells and a simpler, reduced homogeneous phloem ray. The reduction of the phloem rays parallels the differentiation of the axial system.

    Onderzoek naar bruikbare kenmerken ter identificatie van boomen naar hun bast
    Thorenaar, A. - \ 1926
    Wageningen University. Promotor(en): E. Reinders. - Wageningen : Veenman - 207
    bosbouw - floëem - schors, bomen - nederlands indië - cum laude - forestry - phloem - bark - netherlands east indies
    To facilitate further discussions and to inform tropical forestry experts, the formation and anatomy of bark were reviewed in association with its terminology. Sections deal with: secondary phloem; dilation and sclerosis; their influence on primary bark parts and on secondary phloem; interxylary phloem; pith ducts; periderm; lenticels and dead outer bark. Next follows an analysis of what could usually be seen of the anatomy of the bark and the crust with a x 10 lens and with the naked eye. The features noticed were then evaluated as distinctions for bark species. Information was given on odour and taste.

    Then follow descriptions of 60 investigated barks of the Indonesian Archipelago, analysed by these means. A x 10 lens proved sufficient for identification.

    The sequence of bark features from common to special features was shown to be usually: cork layer, stone cells, fibres, soft bark parts, secretory organs, bark rays, while the primary bark parts, often having disappeared, could only serve as distinguishing features for a limited number of barks.

    If the number of bark parts considered were to be further enlarged the use of a x 20 lens might become necessary.

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