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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.

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Adventitious root formation in Arabidopsis : underlying mechanisms and applications
Massoumi, Mehdi - \ 2016
Wageningen University. Promotor(en): Richard Visser, co-promotor(en): Geert-Jan de Klerk; Frans Krens. - Wageningen : Wageningen University - ISBN 9789462578524 - 191
arabidopsis thaliana - adventitious roots - formation - plant development - quantitative traits - etiolation - auxins - explants - molecular biology - gene expression - dna methylation - rooting - ontogeny - plant breeding - arabidopsis thaliana - adventiefwortels - formatie - plantenontwikkeling - kwantitatieve kenmerken - etiolering - auxinen - explantaten - moleculaire biologie - genexpressie - dna-methylering - beworteling - ontogenie - plantenveredeling

Adventitious root (AR) formation is indispensable in vegetative propagation and is widely used. A better understanding of the underlying mechanisms is needed to improve rooting treatments. We first established a system to study rooting in Arabidopsis, the model organism in plant biology but only occasionally used to study adventitious rooting. Inhibition of polar auxin transport reduced AR formation. The role of auxin transporter proteins (several PIN-proteins) was found to be tissue-specific. Maturation (the transition from juvenile to adult) negatively influenced AR formation. Maturation was associated with increased DNA methylation and decreased miR156 level. 5-Azacytidine, a drug that reduces DNA methylation, increased rooting. We also examined the effect of two donor plant pre-treatments, etiolation and flooding, on rooting. Both increased AR formation.

Composite hydrogels of bio-inspired protein polymers : mechanical and structural characterization
Rombouts, W.H. - \ 2015
Wageningen University. Promotor(en): Jasper van der Gucht. - Wageningen : Wageningen University - ISBN 9789462575721 - 172
gels - formation - proteins - polymers - networks - mechanical properties - gels - formatie - eiwitten - polymeren - netwerken - mechanische eigenschappen

In this thesis we presented various combinations of custom-designed protein polymers that formed composite hydrogels. In chapter 2, composite hydrogels were prepared by mixing silk-like block copolymers (CP2SE48CP2) with collagen-like block copolymers (T9CR4T9). We found that by adding the collagen-like protein polymer the storage modulus, the critical stress and critical strain values of the composite hydrogels were significantly improved in comparison to the single networks. With cryo-transmission electron microscopy (cryo-TEM) we observed that the silk-like fibers were bundled in the presence of the collagen-like protein polymer, probably due to depletion attraction interactions. In follow-up research on these composite hydrogels in chapter 3, we tried to get more insight into the exact toughening mechanism and self-healing capabilities of the composite network by performing cyclic loading/unloading tests. We found that mechanical hysteresis occurred in these composite hydrogels. The energy that was dissipated could be split into two contributions: a part belonging to the permanent rupture of silk-like fibers, and a viscoelastic part belonging to the assembly and disassembly of collagen-like triple helices. Both these contributions increased as the concentration of the collagen-like protein polymer in the composite network was increased, resulting in toughening of the composite network. Furthermore, it was observed that the silk-like fiber network was not able to recover, while the composites could recover up to 70% of the original storage modulus after failure. In chapter 4 we studied composite networks of silk-like block copolymers (CP2SE48CP2) and a FMOC-functionalized dipeptide (FMOC-LG) which could both form fibers. With cryo-TEM and atomic force microscopy (AFM) we found that two different types of fibers were formed, indicating that orthogonal self-assembly occurred in this system. We found with rheology that the storage moduli of the composite fiber networks were significantly higher (75 kPa vs. 400 kPa) than that of the single networks. Strain-hardening present in the FMOC-LG fiber network disappeared when the silk-like protein polymer was present. In chapter 5 hydrogels with both physical and chemical crosslinks were prepared from collagen-like protein polymers (T9CRT9). The chemical crosslinks were introduced by crosslinking lysine residues present in the random-coil middle blocks with glutaraldehyde. We found with rheology that the order in which the physical and chemical networks were formed did not influence the final storage modulus of the hydrogel. Depending on the amount of glutaraldehyde added we found an increase of up to an order of magnitude in the storage modulus for the collagen-like hydrogels. To investigate effects on the nonlinear rheological properties cyclic loading/unloading tests were performed. It was observed that before hydrogel failure occurred no hysteresis was observed between consecutive cycles. Both physical and chemical crosslinks ruptured when the hydrogel was fractured. In chapter 6 we studied hydrogels formed by the co- assembly of an asymmetric silk-collagen-like protein polymer (SH8CR4T9) with a symmetric oppositely charged silk-like protein polymer (CP2SE48CP2). This was done in a step-wise approach: (1) the S blocks were co-assembled into silk-like fibers. (2) the T blocks were assembled into triple helical nodes by reducing the temperature. We confirmed with confocal laser scanning microscopy and NMR that both monomers were present in the same fibers. With rheology we found that these composite hydrogels did respond in a reversible manner to temperature changes, with which the mechanical strength of the hydrogel can be tuned. In chapter 7 hydrogel formation of a modified silk-like protein polymer with a cysteine-residue attached to the C-terminal side (CP2SH48CP2-Cys) was studied. With rheology we showed that hydrogels that were formed in oxidizing conditions, where disulfide-bridges could form, were much stronger than those formed in reducing conditions. Both hydrogels formed in oxidizing and reducing conditions showed a scaling of modulus versus concentration consistent with entangled semi-flexible networks. This result implied that the disulfide-bridges formed between cysteine-residues formed loops in the coronae of the fibers. The increase in mechanical strength of the fibers was related to the increase in persistence length of the fibers in oxidizing conditions observed with AFM. With self-consistent field theory-simulations it was shown that the formation of loops in the corona resulted in a slight reduction of the lateral pressure in the corona of the fibers. However, this effect is by itself not sufficient to cause a significant change in persistence length. Due to the reduction in lateral pressure, the stacking of monomers into fibers is probably influenced: fibers with a more crystalline structure and with less detects are formed, resulting in improved mechanical properties of the hydrogels. In the general discussion in chapter 8, we reflect on our work, discuss about future directions of research, and possible applications of protein polymers.

Arsenic analysis in produced formation water (PFW) from Chinguetti FPSO in Mauritania
Korytar, P. ; Galiën, W. van der - \ 2006
IJmuiden : IMARES (Report / IMARES C058/06) - 5
arsenicum - testen - formatie - water - bemonsteren - observatie - discussie - arsenic - testing - formation - sampling - observation - discussion
Woodside Mauritania has commissioned IMARES to organize testing of produced formation water (PFW) from Chinguetti FPSO in Mauritania for arsenic (As (III) and As (V)). This report provides the results of the testing, observations made during the sampling and discussion of the results.
Effect of pentosans on gluten formation and properties.
Wang, M. - \ 2003
Wageningen University. Promotor(en): Rob Hamer, co-promotor(en): Ton van Vliet. - Wageningen : WU - ISBN 9058088286 - 190
tarwegluten - pentosanen - opbrengsten - reologische eigenschappen - formatie - wheat gluten - pentosans - yields - rheological properties - formation
The life cycle of the potato (Solanum tuberosum L.) : from crop physiology to genetics
Celis-Gamboa, B.C. - \ 2002
Wageningen University. Promotor(en): R.G.F. Visser; P.C. Struik; E. Jacobsen. - S.l. : S.n. - ISBN 9789058086884 - 191
solanum tuberosum - aardappelen - solanum phureja - terugkruisingen - genotypen - plantenfysiologie - plantenontwikkeling - knollen - formatie - veroudering - genetische analyse - solanum tuberosum - potatoes - solanum phureja - backcrosses - genotypes - plant physiology - plant development - tubers - formation - senescence - genetic analysis

This thesis describes the results of an analysis of the major developmental events taking place during the life cycle of the potato, based on records from 250 genotypes, from the highly diverse CxE population. The aim was to generate a massive amount of data to build a framework of crop physiological relationships, and use the data to begin with the identification of genetic factors controlling major developmental processes like senescence.

Physiological ageing of seed tubers during storage influences tuber initiation and plant development. Since the majority of the CxE population had short or no tuber dormancy, seed tubers sprouted during storage. Physiological ageing is associated with the intensity of sprouting during storage and with tuber formation after planting. Therefore, it was necessary to investigate the association between sprout length, as an indicator of physiological ageing, and the timing of occurrence of events related to tuber formation and the duration of the plant cycle. Among genotypes of the CxE population, sprout length at the end of the storage period was not strongly related to tuber initiation or other events related to tuber formation. Associations were not found between sprout length and the duration of the plant cycle, plant size and several other variables recorded. We conclude that the variation in sprouting of seed tubers was not the main factor responsible for the large variation observed in the CxE population in the timing of occurrence of tuber formation and plant developmental events.

Despite the large variation found in the CxE population and control varieties in the duration of the plant cycle, all began to form stolons and to flower within a remarkably short period of time. Results strongly suggest that the onset of stolon formation and flowering are not necessarily triggered by an environmental stimulus. The peak production of stolons and swelling stolon tips took place during flowering. However, while in most genotypes, stolon formation was confined to the flowering period, stolon tip swelling proceeded beyond the end of flowering and ended during the senescence period. The number and size distribution of tubers was largely influenced by the degree of stolon branching and the length of the stolon swelling period, and apparently to an smaller extent by the resorption of tubers. Tuber initiation did not have a determinant influence on the timing of stolon formation, stolon tip swelling, flowering and the duration of the plant cycle, contradicting extensive literature supporting the determinant influence of tuber initiation on plant development.

Differences in the timing of events related to plant development and tuber formation were further analyzed after grouping the CxE population according to the duration of the plant cycle. Genotypes with life cycles shorter than 90 days had a small plant size, a short period of stolon formation, stolon tip swelling and flowering, early tuber initiation, very little or no stolon branching and fast progress of canopy senescence. In contrast, genotypes with life cycles longer than 170 days, had a large plant size, profuse and long flowering period, large production of stolons during most of the plant cycle, profuse stolon branching, late but long period of stolon tip swelling and subsequent tuber initiation and slow progress of canopy senescence.

Differences were also found between groups of genotypes in the chronological order at which tuber formation and plant developmental events took place during the plant cycle. Our results show that although in every potato plant there is a period when there is a simultaneous presence of newly formed stolons, swelling stolon tips, tuber incipients and growing tubers, there was no chaos, but a well-orchestrated order influenced by the duration of the plant cycle.

The large variation found in the CE genotypes and varieties in the order of occurrence of morphological events related to plant development and tuber formation demonstrates the remarkable plasticity present in potato and the influence of the selection process during the developing of varieties on the timing of events leading to high yields.

Very high correlations were found between tuber formation and plant developmental events and the duration of the plant cycle (end of the senescence process). In addition, very large differences were found in the CxE population in the onset, duration, mid point and rate of the senescence process. We decided to investigate the genetic factors underlying these variables, describing the process of senescence in potato. We found between two and four QTLs associated with each one of these senescence variables, located on chromosomes 5, 6, 9 and 12. Each one of these QTLs was found in common to at least two of these senescence variables. The effect of these QTLs on different senescence variables was in the same direction, suggesting pleiotropic effects rather than close linkage interactions between these genetic factors. From the QTL analysis of the progress of senescence (amount of yellowing of the plant canopy) during the life cycle of the CxE population, new QTLs were identified, which were present either at the beginning, at the end or during most of the senescence process.

Our results show that the evaluation of variables describing complex traits in a large mapping population, can be a powerful strategy to describe a process at both, physiological and genetic levels.

Formation and stability of emulsions made with proteins and peptides
Smulders, P.E.A. - \ 2000
Agricultural University. Promotor(en): P. Walstra. - S.l. : S.n. - ISBN 9789058083135 - 143
emulsies - formatie - stabiliteit - caseïne - lactalbumine - lysozym - ovalbumine - peptiden - emulsions - formation - stability - casein - lactalbumin - lysozyme - ovalbumin - peptides

The formation and stabilization of oil-in-water emulsions using well-defined and well-characterized proteins and peptides was studied in order to elucidate the relation between their molecular and functional properties. The emulsions were formed with a high-pressure homogenizer. To study the effect of the homogenizer scale on the emulsion properties, emulsions were prepared with a laboratory and a small industrial homogenizer. The flow in the industrial homogenizer was shown to be turbulent. In the laboratory homogenizer, droplet break-up was found to occur in a bounded laminar type of flow, resulting in a poor operating efficiency. The effect of the flow type on the emulsion properties, however, appeared to be small, if the number of passes through the laboratory homogenizer was sufficiently high.

Proteins appeared to have good emulsion forming properties as long as protein aggregation was absent. In those cases, the recoalescence rate during homogenization was found to be similar and only small differences in the droplet size of emulsions could be determined. The surface excess of the emulsion droplets appeared to be governed by the conformational stability and the aggregated state of the proteins. Globular proteins with a high conformational stability yielded relatively low surface excesses, while a flexible random coil protein, likeβ-casein, yielded a relatively high surface excess. Protein aggregation may be due to physicochemical conditions and surface or heat denaturation. If protein aggregates were present, the emulsion droplets were also often aggregated. The droplet size, surface excess, and rate of recoalescence of these aggregated emulsions were usually found to be relatively high.

The emulsion forming properties ofβ-casein peptides appeared to be comparable or superior to those of intact proteins. Amphiphilic peptides without the hydrophobic C-terminal domain ofβ-casein yielded a relatively low surface excess, likely due to strong electrostatic interactions between the highly charged groups of the N-terminal end. The surface excess of emulsions made with hydrophobic peptides with a removed N-terminal domain was comparable to those of emulsions made with intactβ-casein. The peptides were due to their relatively small molar mass more readily desorbed from the oil/water interface than intact proteins.

The coalescence stability of emulsions made with proteins was high even at low protein concentrations and appeared to be mainly determined by the surface excess of the droplets. The emulsion stabilizing properties ofβ-casein peptides were inferior to those of intact proteins probably due to their relatively low molar mass. Comparison of the stability of emulsions made with amphiphilic peptides with an intact or partially removed N-terminal domain showed that this domain was of great importance for providing stability against coalescence. The coalescence stability of emulsions made with hydrophobic peptides was relatively high, which was attributed to the high surface excess of the droplets. The electrostatic and steric interactions appeared to be of great importance for stabilizing emulsions made with peptides against coalescence as was indicated by the effect of changes in pH and ionic strength on the stability.

Keywords: emulsions, formation, stability, molecular properties,β-casein,β-lactoglobulin,α-lactalbumin, lysozyme, ovalbumin, peptides.

Seed development and carbohydrates
Wittich, P.E. - \ 1998
Agricultural University. Promotor(en): M.T.M. Willemse; A.A.M. van Lammeren; C.J. Keijzer. - Wageningen : Wittich - ISBN 9789054858553 - 178
zaadzetting - zaden - formatie - plantenfysiologie - plantenontwikkeling - vruchten - rijp worden - planten - embryologie - metabolisme - plantenvoeding - assimilatie - koolhydraten - vicia faba - gasteria verrucosa - organische scheikunde - seed set - seeds - formation - plant physiology - plant development - fruits - ripening - plants - embryology - metabolism - plant nutrition - assimilation - carbohydrates - vicia faba - gasteria verrucosa - organic chemistry

Seeds assure the plant the onset of a next generation and a way of dispersal. They consist of endosperm and an embryo (originating from gametophytic tissue), enveloped by a seed coat (sporophytic tissue). Plants generate different types of seeds. For instance, the endosperm may either be consumed by the embryo during seed development or retained for use by the embryo during germination. Differences in timing of endosperm digestion can be illustrated with broad bean ( Vicia faba ) and Gasteria verrucosa . Broad bean forms seeds in which the endosperm has been consumed by the fully developed embryo, while the embryo of Gasteria is less developed and surrounded by a large amount of endosperm for use during germination.

An important factor in seed development is the distribution, storage, and utilization of carbohydrates, since carbohydrates are a major source of energy for cell growth. In this thesis the carbohydrate distribution is studied in developing ovules and seeds of maize ( Zea mays ) and Gasteria , by identifying the cells and tissues in which sucrose is degraded. Sucrose is the main carbohydrate supplied by these plants in the developing seeds. The sucrose degrading activity of the enzymes sucrose synthase and invertase indicates the destination of the sucrose transport (Chapters 9 and 10). Immunocytochemical and histochemical techniques are used for the localization of these enzymes in situ .

The results obtained in this study on maize (Chapter 2 and 3) and Gasteria seed development (Chapters 4 and 5) show a general pattern of carbohydrate transport. First, the greatest amount of carbohydrates is applied for the development of the seed coat and nucellus (sporophytic tissues). An example of such a carbohydrate consuming process is the deposition of phytomelan in the seed coat of Gasteria . Phytomelan is a black cell wall component and chemically very inert. Histochemical and electron microscopy observations (Chapters 6 and 7) show that callose forms a mould for the deposition of phytomelan. The breakdown products of callose (glucose monomers and polymers) seem to be used for the synthesis of the phytomelan. Chemical analysis reveals that phytomelan is a complex polyphenolic polymer, and not a melanin (Chapter 8). Second, carbohydrate transport to the sporophytic tissues is followed by transport of most carbohydrates into the endosperm. These carbohydrates will be used for endosperm growth and for storage. Finally the main carbohydrate flow will go to the embryo. The pattern of carbohydrate usage observed in maize and Gasteria was used to generate a general model for angiosperm seed development (Chapter 10). The model explains differences between seeds by relating carbohydrate distribution during seed development to the timing of seed dispersal.

Genetic analysis of seed development in Arabidopsis thaliana = [Genetische analyse van de zaadontwikkeling in Arabidopsis thaliana]
Leon - Kloosterziel, K. - \ 1997
Agricultural University. Promotor(en): M. Koornneef. - S.l. : Leon-Kloosterziel - ISBN 9789054857709 - 119
genen - genomen - mutaties - mutagenese - mutagenen - plantenfysiologie - plantenontwikkeling - vruchten - rijp worden - brassicaceae - zaadzetting - zaden - formatie - kieming - zaadkieming - kiemrust - genes - genomes - mutations - mutagenesis - mutagens - plant physiology - plant development - fruits - ripening - brassicaceae - seed set - seeds - formation - germination - seed germination - seed dormancy

This thesis deals with the genetic aspects of seed development in Arabidopsisthaliana. Mutants affected in several aspects of seed development and, more specifically, in seed maturation have been isolated by various selection procedures. The mutants have been analyzed genetically, physiologically, and morphologically. Some of the mutants are impaired in the biosynthesis or sensitivity to the plant hormone, abscisic acid (ABA). All ABA-related mutants show reduced seed dormancy, indicating the important role of this hormone in the establishment of dormancy. In a direct screen for reduced dormancy, two mutants (rdo) with reduced dormancy were found. These were not ABA-deficient and showed the same sensitivity to ABA, ethylene, auxin, and cytokinin as the wild-type. In contrast to this embryo-determined reduced dormancy, reduced dormancy can also originate in an altered seed coat (testa), like in the altered testa shape ( ats ) mutant. Here, the altered testa shape is caused by a defect in the development of the integuments. Extreme ABA-insensitive mutants ( abi3 ) have green seeds that fail to complete many other aspects of seed maturation, including the induction of dormancy and desiccation tolerance, and the accumulation of seed storage proteins and lipids. In addition to abi3 mutants, lec and fus mutants exhibit such a severely disturbed seed maturation as well, with dark purple seeds due to anthocyanin accumulation. The fus3 mutant shows normal ABA-sensitivity. These various seed maturation mutants indicate that specific genes, some acting dependently and some acting independently from ABA, are responsible for seed maturation programs. The seed maturation mutants were subjected to a physiological and biochemical analysis. A GA-deficient mutant was combined with these mutants. Analysis of these double mutants indicated that seeds of the abi3 and lec mutants did not require GA for germination, in contrast to fus3 seeds. This correlates with ABA-sensitivity for germination. The composition of storage proteins and carbohydrates in abi3 , lec, and fus3 mutant seeds has been compared. The abi3 , lec, and fus3 mutants all showed severely reduced storage proteins. The desiccation intolerance of these seed maturation mutants was not correlated with the lack of specific carbohydrates. Furthermore, the mutants had a higher total content of carbohydrates. This is probably a consequence of the lower levels of storage lipids and proteins.
Physiological constraints to seed growth in perennial ryegrass (Lolium perenne L.)
Warringa, J.W. - \ 1997
Agricultural University. Promotor(en): P.C. Struik; A.J.C. de Visser. - S.l. : Warringa - ISBN 9789054856337 - 139
lolium - plantenfysiologie - plantenontwikkeling - vruchten - rijp worden - formatie - distributie - voedingsstoffenreserves - lolium - plant physiology - plant development - fruits - ripening - formation - distribution - nutrient reserves

The yield of a seed crop of perennial ryegrass varies between I and 2 Mg/ha. This variation is caused by variation in the number of seeds that reach an adequate dry weight. On average 70 % of the seeds present before harvest and cleaning are not recovered because of their low weight. This suggests that seed filling and not seed set determines to a large extent seed yield. Factors influencing seed filling were studied on spaced plants in the greenhouse.

Reducing the light intensity after anthesis from 115 % to 24 % (1.1 MJ/m2) showed that the amount of carbon assimilates in the reproductive tiller was not limiting to seed filling. Seed yield per ear was reduced by only 14 % and average seed dry weight by only 4 %. Although the amount of water-soluble carbohydrates (WSC in the stem + rachis was strongly reduced at 24 % light, it could have supported an extra 37 % of seed yield.

New vegetative tillers that developed after anthesis did not reduce seed filling and seed yield per ear because of the large amount of WSC reserves in the stem. Regrowth of tillers cut at anthesis strongly reduced WSC stem reserves.

The large variation of seed dry weight within the ear could for about 60 % be attributed to differences in rate of growth and for about 30 % to differences in duration of growth. The differences in growth rate were determined by the ovule dry weight at anthesis and not by differences in relative growth rate. The availability of assimilates and the accumulation of starch did not differ between seeds within the ear. Differences in the duration of growth were mainly caused by differences in time of anthesis, not ripening. The interaction between seeds in the ear was weak; removal of spikelets or seeds within a spikelet did not strongly affect the remaining seeds. Apparently processes in the seed itself mainly determine seed filling and seed yield of perennial ryegrass. Factors controlling ear development determine the ovule dry weight at anthesis and thus to a large extent the variation in final seed dry weight within the ear.

Research for the development of sago palm (Metroxylon sagu Rottb.) cultivation in Sarawak, Malaysia
Jong, F.S. - \ 1995
Agricultural University. Promotor(en): M. Flach. - S.l. : Jong - 139
metroxylon sagu - sago - plantenvermeerdering - beplanten - formatie - distributie - voedingsstoffenreserves - geslachtelijke voortplanting - sarawak - metroxylon sagu - sago - propagation - planting - formation - distribution - nutrient reserves - sexual reproduction - sarawak
General introduction (Chapter 1)

This chapter contains an overview of knowledge with respect to the cultivation of the true sago palm (Metroxylon sagu). The palm flowers once and forms suckers or tillers. Seedlings grow into a rosette stage of leaves and trunks are only formed after 4-6 years. The trunk may reach a length of 6-14 m and possess a trunk of 7-24 feathered leaves. An enormous inflorescence heralds the end of the life cycle. Formation of the inflorescence, for which the starch in the trunk is being used, begins 4-14 years after the start of trunk formation.

Continuous suckering multiplies the palm vegetatively, forming a cluster around the leader palm. Suckers are commonly used for vegetative propagation by man. Since time immemorial, man uses the sago palm trunk as a source of food starch in South East Asia. It has been a commercial crop of smallholder farmers on peat soils in Sarawak for a long time. At present, Sarawak exports nearly 50,000 tonnes air-dried sago palm starch.

Since 1982, the Sarawak Government tries to improve and increase its cultivation, as it is one of the few crops that can be grown with reasonable success on the rather wet deep peat soils. For this purpose, a research station has been established at Sungai Talau Station and a laboratory in Mukah. The semi-govern mental agency for land development, Land Custody and Development Authority, is planting sago on some ten thousands of hectares, in order to develop part of the 1.5 million ha of poorly drained peat soils.

The chapter ends with an overview of the main limiting factors for sago palm cultivation. This lead to the research presented in this thesis.

Factors affecting the subsequent survival rate of sago palm suckers in the nursery (Chapter 2).

Suckers are the most popularly used planting material for establishing sago palms in smallholder gardens and plantations in Sarawak. In nurseries, the mortality rate of suckers is around 20-40%. In the dry season, higher mortality rates are common.

Factors suspected to affect the subsequent survival rate of sago palm suckers in nurseries were investigated. The survival of suckers was significantly enhanced if they were planted promptly, best if it was within three days after removal from the parent palm. Suckers stored for more than two weeks before planting generally showed a marked decrease in their subsequent survival in the nursery. When the cutends and the whole or part of the rhizome were completely buried in the soil, an increased rate of survival was also obtained. Rhizomes planted 8 cm below the soil surface or just placed on top of the soil surface had lower survival rates. Trimming of roots to as short as 1 em did not affect the subsequent survival of the suckers. Trimming of the rhizomes to a length close to the growing point of the sucker was deleterious. Shading of suckers during the dry season appeared to contribute positively to their successful establishment.

When planting of suckers was delayed, treatment with a wide-spectrum fungicide while storing the suckers in cool and moist places was shown to reduce their mortality rate.

Effects of sucker size on the establishment of sago palms (Chapter 3).

The effects of sucker size on their subsequent establishment were investigated. Suckers of all sizes from 5 to 25 em in base diameter were established successfully without mortality. In general, larger suckers of 15-25 em in base diameter are faster in their establishment. However, these suckers are heavy, bulky, less abundant, and expensive to handle. In large- scale cultivation of sago palms, the use of large suckers has to be weighed in financial terms and availability of the material. It appears that larger suckers may be suitable for smallholder cultivation. In plantations, smaller suckers of 7-10 em in base diameter are recommended.

Effects of plant spacing on the growth and development of sago palms on undrained deep peat (Chapter 4).

The growth of sago palms was compared at 4.5 m, 7.5 m, 10.5 m and 13.5 m square planting. Palms spaced at 4.5 m had the lowest frond emergence rate, smallest trunk circumference at the base and at 1 m above ground level (a.g.l.), shortest prostrate (ground)trunk, longest fronds with thinnest rachides and the smallest crown size. They produced the least numbers of trunks and suckers, and their canopy was closed before trunk formation commenced in the third to fourth year after field planting.

The vegetative growth was intermediate in the 7.5 m spacing treatment. Compared to 4.5 m spacing, these palms had significantly higher frond emergence rate, larger crown size and trunk circumference, better stem formation and suckering ability as well as shorter fronds with thicker rachides. Their canopy was closed by the fifth to sixth year after planting. However, when compared to the 10.5 m and 13.5 m spacing treatments, the 7.5 m treatment palms had significantly smaller crown size, lower frond production rate, longer fronds and thicker rachides, smaller trunks at 1 m a.g.l. and slower trunk formation. There were no differences among these treatments in the suckering ability and the size of the basal circumference of the trunk.

Significant differences between spacing treatments of 10.5 m and 13.5 m were only found in the frond length, sucker number and frond production rate. However, the canopy of palms spaced at 10.5 m was about to close in the eighth year whereas those spaced at 13.5 m remained open. No difference was found in the average trunk height between any two spacing treatments.

The formation and growth of sago palm trunks were suppressed at 4.5 and 7.5 m spacing whereas at a spacing of 13.5 m, the field was under-utilized. Among the spacing treatments, the maximum trunk production per unit area was from palms spaced at 10.5 m. This suggests that sago palm on peat should be cultivated at a spacing of about 10 m.

Distribution and variation in the starch and moisture contents of sago palms at different growth stages (Chapter 5).

Sago palms of similar growth stages established on shallow peat vary in length, circumference and weight of their trunks. From the time of planting, a sago palm remains in the rosette growth stage for about 5.5 years before trunks are formed. Flower initiation occurs at 12.5 years and the fruit drop is completed in 14.5 years.

The average content and density of dry starch increases with increasing maturity of the sago palm until flowering. Maximum starch content of 18-20% is found between the full trunk growth stage (just before the emergence of inflorescence structure) and flowering stage. Thereafter, the starch content decreases sharply and remains finally at about 4 - 6%.

The moisture content is high and remains rather constant along the trunk of young sago palms. As the palm matures, moisture content decreases, especially in the lower portion of the trunk.

The lowest mean moisture content is found in palms from the full trunk growth stage to flowering stage, corresponding to the highest starch content in the trunk. In young and over- mature palms, the mean moisture content is higher. A high negative correlation (r2 = -0.85) is found between moisture and starch contents, showing the mutual replacement of starch and moisture in the trunk.

Within each growth stage, the density of the fresh trunk is constant along the entire trunk length. However, among different growth stages, the mean density of the sago palm trunk increases gradually from the early trunk formation stage. It reaches a maximum between the full trunk growth and flowering stage before decreasing in the subsequent over-mature stages.

This study provides an understanding of the pattern of starch accumulation and the relationship between the fresh density of the trunk and the starch content in it. This enables the harvesting of palms at the correct growth stage for maximum starch yield per unit time, and facilitates the grading of sago logs for starch yield based on their buoyancy.

Flowering biology of the sago palm (Chapter 6).

Scaffolds were constructed below the gigantic inflorescence of sago palms to investigate the flowering biology. In the early stage of development, flower buds occur in pairs in a bracteole. One is a staminate (male) and the other a hermaphrodite (perfect) flower. During development, abortion of either the staminate or the hermaphrodite flower buds occurs. By anthesis, mainly single flower buds are left in each bracteole. The sago palm is andromonoecious as indicated by the presence of staminate and hermaphrodite flowers in the same inflorescence. In three of the seven palms investigated, abnormal hermaphrodite flowers which opened prematurely were encountered.

The duration of flower opening in the entire inflorescence is about 30 days for the staminate flowers and 50 days for the hermaphrodite flowers. For the abnormal hermaphrodite flowers, opening may stretch over a period of three months and the premature stamens die during the opening. The peak of daily flower opening is between 1100-1400 hours. To a large extent, the sago palm is protandrous but overlaps in the opening of staminate and hermaphrodite flowers do occur. Seedless fruits are formed in all these palms. Visiting insects ( predominantly Trigona itama, Trigona apicalis and Apis dorsata) are found in great numbers during anthesis. However, only seedless fruits develop in most palms. This suggests that the pollen and pistil of sago palms may be self - incompatible. Bagging experiments to exclude visiting insects suggest that cross- pollination is obligatory in sago palms.

.In the current investigation, each sago palm produced between 276,000-864,000 mature flower buds and 2174-6675 mature fruits. The duration of fruit growth from anthesis to last fruit drop is between 19-23 months.

Germination of sago palm seeds (Chapter 7 ).

Some practical methods to increase the germination rate of sago palm seeds were investigated. The capability of seeds to germinate was found to increase as seed maturity advanced. Germination tests conducted on mature sago palm seeds using wet sand tray showed that removal of the husk and husk plus fleshy tissue (sarcotesta) enhanced germination. Loosening of the operculum and treatment with 10' M gibberellin also increased the number and speed of germination. Brief treatment with concentrated sulphuric acid was found fatal to the seeds. Germination of the entire sago palm fruit required an environment with high humidity. An easy and effective way of achieving this is to put mature sago palm fruits in partially permeable Hessian sacks placed in a damp atmosphere.

General conclusions (Chapter 8)

In this chapter, an assessment of the research results for practical application in sago cultivation is given.

Application of the findings from experiments on the survival of suckers may lead to an increase of survival between 10 and 40%. At the current cost of about RM 3.50 per sucker, this will decrease cost of planting, at the present planting distance, between RM 72 and RM 290 per hectare. Selecting suckers with a base diameter between 7 and 10 cm and a weight between 2 and 5 kg can reduce transportation and handling costs. This may also prevent price increase due to temporary sucker shortage when larger planting materials are preferred . Planting sago palms in a 10 m square pattern, with possibly a temporary plant in the middle of the square for oneharvest trunk , appears optimal for ultimate production. Findings in the distribution of starch in the trunk at different growth stages leads to harvesting just before flowering. Based on the ralation found between starch content, moisture content and trunk density, it may lead to the development of a practical method to estimate the starch content of a trunk based on its buoyancy. The results obtained in flowering and seed germination appear to be important and may be used for future breeding and research programmes. Sago palm seeds may also be used for new planting if suckers are either too expensive or in short supply.

The most pressing problems that needs attension in sago research is fertilizer application on the notoriously poor and badly drained peat soils. It is also important to start research on shortening the unproductive phase of the cultivation.

Fruit growth and dry matter partitioning in cucumber
Marcelis, L.F.M. - \ 1994
Agricultural University. Promotor(en): H. Challa; S.C. van de Geijn. - S.l. : Marcelis - ISBN 9789054853107 - 173
cucumis sativus - komkommers - formatie - distributie - voedingsstoffenreserves - groei - fotosynthese - cucumis sativus - cucumbers - formation - distribution - nutrient reserves - growth - photosynthesis

In this thesis, dry matter partitioning into different plant parts of generative cucumber plants was quantitatively studied as a dynamic process in terms of an internal competition among organs for assimilates in relation to external factors, such as the greenhouse climate and cultural practices. As the fruits represent the major sink organs and as they are of economic interest, special attention was paid to the growth and development of the individual fruits.

During a growing season the fraction of dry matter partitioned into the fruits changed cyclically between 40 and 90%. Dry matter partitioning appeared to be primarily regulated by the sinks (fruits). Source strength influenced the number of fruits on a plant and, therefore, indirectly influenced the dry matter partitioning, although after a lag phase. No feed-back effect of the number of fruits per plant on source strength (leaf photosynthesis) was observed, unless all fruits were removed for a prolonged period.

The growth rate of an individual fruit, but not its development, was strongly dependent of the assimilate supply. Fruit development appeared to be closely related to the temperature sum. The growth rate increased with increasing temperature, but the effect on final fruit weight depended on the level of assimilate supply. Irradiance affected growth of individual fruits via effects on assimilate supply, but had no photomorphogenetic effect. During fruit ontogeny, cells expanded continuously, but cell division was restricted to the first part of the growing period. Although usually the size of the cucumber fruit positively correlated with the number of cells, cell number was not an important determinant of fruit size.

Fruit photosynthesis contributed only to a small extent (1-5%) to the cumulative carbon requirement of a fruit. Thirteen to 15% of the cumulative carbon requirement of a fruit was respired. The respiratory losses as a fraction of the carbon requirement of a fruit changed during fruit ontogeny, but were independent of temperature and were similar for slow and fast growing fruits.

A dynamic model was developed for the simulation of the daily dry matter partitioning. In the model dry matter partitioning was simulated as a function of sink strengths of the plant organs, where sink strength of an organ was described by its potential growth rate. Model results agreed well with the measured data.

Tuber formation in the wild potato species Solanum demissum Lindl.
Helder, J. - \ 1994
Agricultural University. Promotor(en): J. Bruinsma; P.C. Struik; D. Vreugdenhil. - S.l. : Helder - ISBN 9789054852049 - 113
plantenfysiologie - plantenontwikkeling - wortelstokken - knollen - formatie - distributie - voedingsstoffenreserves - solanum tuberosum - aardappelen - solanaceae - solanum demissum - vegetatieve organen van de plant - plant physiology - plant development - rhizomes - tubers - formation - distribution - nutrient reserves - solanum tuberosum - potatoes - solanaceae - solanum demissum - plant vegetative organs
1. How does a potato plant form tubers?

Potato plants produce sexual multiplication and survival structures, true seeds, and asexual multiplication and survival bodies, tubers. Berries of the potato plant contain a large number of minute seeds. Relatively large tubers are formed in the soil in the subapical part of the stolons. The genetically heterogeneous seeds of a potato plant will spread in a larger area than its tubers, whose radius of spread is restricted by the length of the stolons. Potato tubers from one plant are genetically identical (to each other and to the mother plant) and reside in the soil, a relatively sheltered environment. Contrary to germinating seeds, the sprouts on a potato tuber have access to a relatively large quantity of storage food. A potato plant invests a lot of dry matter into the tubers. Apparently, tubers are, apart from being a valuable agricultural product, important structures for the potato plant itself. In this thesis 1 focused on tuber induction (Chapters 2 and 3), and changes in sucrose metabolism in stolon tips as a result of tuber induction (Chapters 4, 5 and 6).

A series of long nights and a relatively low night temperature favour tuber induction in tuber- forming Solanum species. As a result of exposure to these conditions a potato plant synthesizes a (set of) compound(s) in the leaves, which is (are) transported basipetally to the stolon tips. During the last thirty years, it was surmised that this (set of) compound(s) consisted of a (mix of) classical plant hormones. However, no (mix of) plant hormone(s) could be identified as the tuber inducing principle yet.

The starting point for this research project was the finding of Struik et al. (1987) that tuber inducing activity is present in extracellular extracts from leaflets of tuber-bearing Solanum tuberosum plants. An important indication that this activity is related to tuber induction would be its absence in non-tuber-bearing plants from the same age. However, tuber formation in commercial West-European S. tuberosum cultivars cannot be prevented by a simple shortening of the nightlength. Therefore, it was decided to switch to a wild Solanum species that only forms tubers under short-day conditions. S.demissum, a Mexican Solanum species which habits resemble S.tuberosum, meets this prerequisite. Tubers are formed when plants are exposed to 10 h daylength, whereas no tuber formation is observed when the daylength is extended to 16 h.

2. The role of (hydroxylated) jasmonic acids in tuber induction

Yoshihara, et al. (1989) isolated and characterized a substance from leaves of tuber-bearing potato plants (Solanum tuberosum, cv. Irish Cobbler) which they called 'tuberonic acid'. 'Tuberonic acid' is a glucoside of 12-hydroxy-jasmonic acid (12-OH-JA). This finding prompted us to investigate whether the tuber-inducing activity found in extracts from potato leaflets could be attributed to the presence of 'tuberonic acid'. Assuming 'tuberonic acid' to be involved in tuber induction, it is to be expected that this substance is absent in leaflets from non- tuber-bearing S.demissum plants.

Extracts of leaflets from S.demissum plants grown under long- (LD) and short-day (SD) conditions were analyzed. The aglycon of 'tuberonic acid', not its glucoside, was detected in leaflets from SD plants. Moreover, a second hydroxylated jasmonic acid was detected: 11-OH-JA. It was the first time that this compound was detected in higher plants (Chapter 2). As a native substance it was detected before in a fungus, Botryodiplodia theobromae, by Miersch et al. (1991). Because no deuterated hydroxylated JAs were available, we could not determine the absolute concentrations of 11- and (12-OH-JA). in SD leaflets. However, the level of 11-OH-JA of SD leaflets was higher than the (12-OH-JA). level. No hydroxylated JAs were detected in LD leaflets.

Hydroxylated JAs are metabolization products of JA. The CA concentrations in LD and SD leaflets did not differ significantly. Hence, tuber induction in S.demissum is correlated with the hydroxylation of CA A number of diurnal cycles of long nights and relatively cool temperatures will finally result in either the formation or activation of CA hydroxylating enzymes or the neutralization of the spatial separation between enzyme and substrate.

Whether hydroxylated JAs are causally related to tuber induction remains to be proven. CA was found to induce the formation of tubers on S.demissum explants in vitro . Hydroxylated JAs could not be tested because only minute amounts of these substances were available. The reason why CA itself is apparently not involved in tuber induction inplanta could be its apolarity. Apolarity prevents basipetal transport of a compound via the phloem. Hydroxylated JAs can be easily glycosylated, and become transportable. This hypothesis is only apparently conflicting with the observation that CA can induce tuber formation in vitro. In the bioassay, stem pieces with axillary buds were placed in the JA-containing, solidified nutrient medium, so no transport of CA via the phloem was needed.

3. Reception of a tuber-inducing substance in a stolon tip

Tuber induction in potato plants is irregular: only a subset of the stolon tips available will start to swell subapically after exposure to tuber-inducing conditions. The vasculature of potato plants excludes the possibility that a subset of stolon tips would be solely connected with a certain subset of leaves that does or does not synthesize a tuber-inducing signal. Nevertheless, this misconception persists in the literature.

We monitored external characteristics of 841 stolon tips from 6 plants exposed to SD conditions. It was investigated whether a correlation could be found between subapical swelling and branching order, stolon and stolon-branch age, longitudinal growth rates of stolons and stolon branches, and attachment of the stolon to the main stem. No correlation was found between tuber formation and one of these external characteristics (Chapter 3). It is concluded that tuber initiation in S.demissum depends on metabolic or hormonal conditions in stolons or stolon branches, which are insufficiently reflected in external characteristics of these stolons or stolon branches to indicate the change of longitudinal growth into radial growth.

4. Tuber induction and concomitant changes in sucrose metabolism in stolon tips

High concentrations of sucrose induces tuber formation in S. tuberosum explants in vitro (e.g. Hussey and Stacey 1984) as well as the expression of genes coding two semi-tuberspecific proteins, patatin (Wenzler et al. 1989) and proteinase inhibitor II (Johnson and Ryan 1984). We decided to investigate whether changes in the sucrose metabolism could be observed in the stolon tip before or during tuber initiation.

The mono- and disaccharide contents of individual stolon tips of different developmental stages were determined qualitatively and quantitatively. No (transient) increase of the sucrose concentration could be detected concomitant with tuber initiation. The sucrose concentration was constantly low in developing stolon tips, and only tended to increase in relatively large tubers. However, we could not be conclusive about this since sucrose measurements were done at stolon tips as a whole. Very local (transient) sucrose accumulations could not be excluded. Recently, Müller-Röber et al. (1992) showed that a constitutively high sucrose concentration in potato tuber does not lead to an enhanced expression of patatin or proteinase inhibitor II. It illustrates that phenomena observed in in vitro systems do not necessarily occur in planta. Apart from sucrose, glucose and fructose were the main sugars in stolon tips. The glucose concentration decreased gradually during the process of subapical swelling whereas the fructose concentration dropped (Chapter 4).

Invertases catalyze the irreversible hydrolysis of sucrose into glucose and fructose. Acid invertase activity is high in non-swollen stolon tips and decreases during subapical swelling. A specific neutral invertase could not be detected in stolon tips (Chapter 5).

Sucrose synthase catalyzes a reversible reaction in which UDP and sucrose are converted into UDP-glucose and fructose. Sucrose synthase activity is barely detectable in non-swollen stolon tips. From the onset of subapical swelling onwards sucrose synthase activity increases rapidly (Chapter 5).

The decreasing glucose concentration could be attributed to an increase of the sucrose synthase activity relative to the acid invertase activity in the stolon tip. On the other hand, sucrose splitting results in the formation of fructose irrespective of the nature of the enzyme involved. The steep decrease of the fructose concentration could be explained by a spatial shift: acid invertase activity is restricted to the cell wall or the vacuole, an environment where hexose kinases are relatively inactive, whereas sucrose synthase activity occurs in the cytosol. The fructose level in stolon tips drops in developing tubers, because sucrose splitting takes place in the cytosol. Here, fructose is exposed to a high activity of hexose kinases. The rate of fructose phosphorylation in extracts from stolon tips of S.demissum is manifold higher than the rate of glucose phosphorylation (Chapter 4). In Chapter 6, the consequences of the above mentioned enzyme and spatial shift on levels of several phosphorylated sugars were determined.

Potato tubers; everybody can tell you what they look like and how they taste. Most people will recognize a potato crop in the field. At the same time, nobody can tell you how a potato plant starts to form tubers. It is a fascinating subject to do research on, and maybe this thesis comprises a few little steps towards a better understanding of this phenomenon.

Development and dry matter distribution in glasshouse tomato : a quantitative approach
Koning, A.N.M. de - \ 1994
Agricultural University. Promotor(en): H. Challa. - S.l. : De Koning - ISBN 9789054853329 - 240
solanum lycopersicum - tomaten - groei - gewassen - formatie - distributie - voedingsstoffenreserves - computersimulatie - simulatie - simulatiemodellen - droge stof - solanum lycopersicum - tomatoes - growth - crops - formation - distribution - nutrient reserves - computer simulation - simulation - simulation models - dry matter

In the glasshouse cultivation of a long-season tomato crop, maximum fruit production is obtained when there is a proper balance between the demand and the supply of assimilate, and an optimum proportion of vegetative growth throughout the season in order to sustain the crop photosynthetic capacity. These aspects of crop growth are mainly affected by the fruit load, defined as the assimilate demand of all fruits together. In practice fruit load is controlled by plant density, fruit thinning and temperature. These measures for crop control can be more precise and effective if their effects are known in quantitative terms. An explanatory dynamic growth model was developed that simulates assimilate demand and dry matter distribution in an indeterminate tomato crop. Number of growing organs was evaluated through prediction of initiation, abortion and harvest of individual organs. Assimilate demand was based on potential organ growth rates (growth at nonlimiting assimilate supply). Dry matter distribution in the model was in proportion to the potential growth rates of the organs.

In total 11 glasshouse experiments were conducted, six of which included temperature treatments. Truss formation rate increased with temperature (17-27°C) and declined with plant age. Truss formation rate was found to depend on the genotype, while fruit load, plant density, season and electrical conductivity of the root environment (EC: 0.3-0.9 S m -1) had no effect. The number of fruit that develop per truss was positively correlated with the vegetative growth of the top of the plants. The duration of the fruit growth period (time between anthesis and start of colouring) was shortened with increasing temperature, young and old fruits being the most sensitive. At the same air temperature the fruit growth period in summer was shorter than in spring. Fruits of old plants had slightly longer growth period than fruits of young plants. Potential weight of the fruits at harvest was negatively correlated with temperature, mainly due to the shorter fruit growth period. Further, the potential size increased with ontogeny, which effect was more pronounced in early than in late spring. The course of potential weight in time was described by a Gompertz growth curve exhibiting the maximum growth rate at about 40% of the fruit growth period. When during fruit development a fruit changed from limiting to nonlimiting assimilate supply, it did not immediately reach the same growth rate as fruits grown constantly at nonlimiting assimilate supply., A mechanism is proposed that explains this phenomenon. The fraction of dry matter distributed to vegetative growth declined substantially with temperature. The (apparent) potential growth rate of a vegetative unit at 24°C was estimated to be as much as 50% lower than at 19°C. The dry matter-content of fruits was negatively correlated with temperature and EC of the root environment and was higher in summer than in spring and autumn.

The model was tested with data from five commercial crops. Truss formation rate, fruit growth period and dry matter distribution were predicted reasonably well. The modelling of the number of fruits per truss requires more investigation. Simulated assimilate demand of a mature tomato crop reached values of 10 and 60g CH 2 O m -2d -1for maintenance respiration and growth respectively. The potential growth rate (as defined by the sinks) appeared to be about twice the actual growth rate.

A simulation study indicated that maximum fruit production of tomato is probably obtained at a fairly low leaf area index (2-3 m 2m -2). At supra-optimum leaf area index additional leaf area for extra light interception requires more assimilate than it would produce. Computations showed that in spring and early summer the optimum plant density is determined by the required number of fruits (sink capacity) whereas in summer a combination of high plant density and fruit thinning seems required for sufficient leaf area. The results are discussed with respect to the crop sink-source system and temperature control in the glasshouse. Prospects for practical applications of the model are presented.

Onderzoek naar factoren en processen die de produktie en kwaliteit van witlof beinvloeden : eindverslag project 729
Reerink, J.R. - \ 1993
Wageningen : CABO-DLO (Verslag / CABO-DLO 170) - 174
cichorei - cichorium intybus - gewassen, groeifasen - distributie - formatie - groeistadia - voedingsstoffenreserves - chicory - crop growth stage - distribution - formation - growth stages - nutrient reserves
Abscisic acid and assimilate partitioning during seed development
Bruijn, S.M. de - \ 1993
Agricultural University. Promotor(en): C.M. Karssen; D. Vreugdenhil. - S.l. : De Bruijn - ISBN 9789054851851 - 147
abscisinezuur - distributie - voedingsstoffenreserves - plantenfysiologie - plantenontwikkeling - vruchten - rijp worden - fabaceae - pisum sativum - erwten - brassicaceae - formatie - groei - abscisic acid - distribution - nutrient reserves - plant physiology - plant development - fruits - ripening - fabaceae - pisum sativum - peas - brassicaceae - formation - growth

This thesis describes the influence of abscisic acid (ABA) on the transport of assimilates to seeds and the deposition of reserves in seeds. It is well-known from literature that ABA accumulates in seeds during development, and that ABA concentrations in seeds correlate rather well with seed size and seed growth rates. However, since ABA is at least partly synthesized in the leaves and transported to the seeds via the phloem, a correlation between ABA levels and growth rate can easily be explained as the result of the combined transport of ABA and assimilates. Reports about the effect of applied ABA on transport of assimilates to seeds are contradictory (Table 1.I). Moreover, application of ABA has several disadvantages: the application technique itself may cause artefacts, and the results are difficult to interpret since the endogenous ABA level after application depends on penetration, transport and metabolism in the tissue. For these reasons, we have chosen for a different approach, viz . the use of hormone mutants. Two species were used: Pisum sativum and Arabidopsis thaliana .

Growth and development of the ABA-deficient ' wilty ' mutant of pea is described in detail (Chapter 2). A non-wilty isogenic line was obtained after six successive backcrosses of the mutant with a closely approximating line. The plants were grown at conditions of high relative humidity and cultured on hydroponics, since leaves of ABA-deficient plants fail to accumulate ABA at drought stress and consequently do not close their stomata- For the same reason, mutant leaves have a higher dry matter content than wild-type leaves. The mutant grew slower and especially root growth was reduced; this resulted in a considerably larger shoot/root ratio. Similar effects have been found in ABA-deficient mutants of several other species. This root-growth promotive effect of ABA can be explained as a measure to prevent an undesirable water status of the leaves by increasing the volume of soil explored under dry conditions.

ABA-deficient plants had fewer and smaller seeds than wild-type plants, but since the mutants plants themselves were also smaller, the weight ratio of reproductive to vegetative parts was similar in both lines. The seeds of mutant plants contained about five times less ABA than wild-type seeds. It was concluded that the lower growth rate of both vegetative and reproductive parts was not directly caused by the lower ABA content of these organs, but by disturbed water relations.

One of the reasons to choose the pea mutant was that transport of assimilates to legume seeds can be studied by the empty-seed-coat technique. After removal of a part of the pod wall and the seed coat, the embryo is replaced by a buffer, while leaving most of the maternal tissue intact. This buffer receives assimilates from the seed-coat and is regularly analysed for the presence of sucrose. The rate of sucrose efflux calculated from the seed-coat into the medium is assumed to be a measure for phloem import, especially during the period of near-constant sucrose release (4-10 hours after the start of the experiment). The effect of ABA on sucrose release was studied by applying various ABA concentrations to the buffer (Figure 3. 1) and expressing the amount of sucrose released into these buffers relative to the amount present in a control seed-coat (a surgically modified seed-coat containing buffer without ABA). It was shown that hardly any ABA leaked from one seed-coat to another. The experiments were performed with both wildtype and ABA-deficient plants, either or not at source-limited conditions, since it was assumed that a possible effect of ABA might be more pronounced in ABA-deficient plants and at source-limited conditions. Source-limiting indeed caused a reduction of the sucrose release- rate. However, no effect of ABA on sucrose release could be discerned, irrespective of the experimental conditions.

Another advantage of the use of mutants is the possibility to study competition between genetically different seeds, for the same source of assimilates (Figure 1.3). In pea, this was achieved by crossing an ABA-deficient mother plant with pollen from plants that were heterozygous for this trait. Chapter 4 describes experiments on ABA-deficient pea plants bearing pods with both ABA-deficient and ABA-containing seeds in the same pod. Seeds in the same pod usually have the same growth rate. In these pods, the growth rate of the seeds was determined by measuring the diameter of the seeds with a pair of callipers. In a control experiment it was shown that these manipulations (opening of the pod and measuring the seeds) did not disturb the normal growth pattern of the seeds. No effect of the genotype on the growth rate of the seeds was detected.

Similar studies were performed with Arabidopsis mutants (Chapter 5). In one series of experiments, successive flowers of a recombinant of an ABA-deficient and an ABA-insensitive mutant (aba,abi3) were alternatingly pollinated with pollen from either wildtype or double-mutant plants. In another series of experiments, a double-mutant that was both ABA-deficient and starchless was used as a mother plant; the amount of available assimilates in these plants was reduced by decreasing the light intensity. The growth rate of the seeds was determined by exposing the mother plants to radiolabelled CO 2 and detecting the amount of radioactivity in the seeds. The weight of the seeds of these crosses was determined on a high-precision balance. In these experiments, again no significant influence of the genotype on either the import of radioactivity or the weight of the seeds could be detected.

The possible effect of ABA on the deposition of reserve material in seeds was studied with some Arabidopsis mutants. Arabidopsis is a crucifer and its seeds initially accumulate starch which is degraded and converted to lipids during seed maturation. Seeds of the ABA-deficient (aba) and the ABA-insensitive (abi3) mutant and their recombinant (aba,abi3) were collected during development and their lipid and carbohydrate composition was analysed and compared with wild-type seeds. The maximum dry and fresh weight of the seeds was not influenced by the genotype. All mutants had considerably reduced levels of eicosenoic acid (20: 1) in the triacylglycerol fraction as compared to wild- type seeds; it is concluded that ABA is involved in the regulation of elongation of fatty acids. The total amount of neutral lipids in seeds of the single mutants was similar to that in wild-type seeds (about 30-35 % on a dry weight basis), but doublemutant seeds contained only half this amount. On the other hand, double-mutant seeds had elevated levels of starch and soluble sugars. Apparently, the blockade in lipid synthesis in these mutants is so strong that it results in starch accumulation and finally in accumulation of soluble sugars. It is concluded that both the presence of ABA and the sensitivity to ABA are required for normal acyl-chain elongation and lipid accumulation; the absence of both factors results in a higher proportion of the imported assimilates being stored as carbohydrates.

From the above-mentioned experiments, it was concluded that ABA has no major influence on the long-distance transport of assimilates, at least not in the species Pisum sativum and Arabidopsis thaliana. However, ABA appears to be involved in the distribution of assimilates over the various types of storage material during seed development.

Beperking van besvorming in aarappelen met behulp van groeiregulatoren en het effect daarvan op de opbrengst en kwaliteitPrevention of berry formation in potato plants by single foliar applications of growth regulators and their effects on tuber yield and quality
Veerman, A. - \ 1991
In: Jaarboek 1987-1992 : verslagen van in 1987-1992 afgesloten onderzoekprojecten op Regionale Onderzoek Centra en het PAGV Lelystad : Proefstation voor de Akkerbouw en de Groenteteelt in de Vollegrond (Publikatie / Proefstation voor de Akkerbouw en de Groenteteelt in de Vollegrond, Regionale Onderzoekcentra no. 38-64) - p. 20 - 27.
formatie - prestatieniveau - plantengroeiregulatoren - aardappelen - productie - kwaliteit - zaadzetting - zaden - solanum tuberosum - formation - performance - plant growth regulators - potatoes - production - quality - seed set - seeds
Woningonderhoud in zwart, wit of grijs?
Bunk, A.R. ; Wunderink, S.R. - \ 1990
Tijdschrift voor huishoudkunde 11 (1990). - ISSN 0169-1295 - p. 8 - 14.
do it yourself activities - dwellings - economic sectors - formation - housing - improvement - management - national income
Opslag en benutting van niet-structurele koolhydraten in de vegetatieve delen tijdens bloei en zaadvulling bij zaadgewassen : een literatuur-orientatie
Dijk, W. van - \ 1989
Wageningen : CABO (CABO-verslag nr. 116) - 41
aldehyden - koolhydraten - cellulose - distributie - formatie - ketonen - voedingsstoffenreserves - zaadzetting - zaden - zetmeel - aldehydes - carbohydrates - distribution - formation - ketones - nutrient reserves - seed set - seeds - starch
Dry matter distribution in tomato and cucumber.
Heuvelink, E. ; Marcelis, L.F.M. - \ 1989
Acta Horticulturae 260 (1989). - ISSN 0567-7572 - p. 149 - 157.
computersimulatie - komkommers - cucumis sativus - distributie - droge stof - formatie - solanum lycopersicum - voedingsstoffenreserves - teelt onder bescherming - simulatie - simulatiemodellen - tomaten - computer simulation - cucumbers - distribution - dry matter - formation - nutrient reserves - protected cultivation - simulation - simulation models - tomatoes
A model to simulate dynamically the distribution of dry matter between leaves, stem, roots and individual cucumber fruits or tomato clusters of fruits is described. The simulated dry matter distribution is regulated by the sink strengths of the plant organs. These sink strengths can be quantified by their potential growth rates, i.e. the growth rates under conditions of non-limiting assimilate supply. Potential dry weight and time from flowering until harvest of tomato clusters of fruits decreased with increasing temperature (17, 21 or 25 °C). However, the relation between sink strength (potential growth rate) and developmental stage of a cluster (time after flowering / time from flowering until harvest) appeared to be almost independent on temperature. In the model the sink strengths of leaves, stem and roots were assumed to be constant. For cucumber the dry matter distribution between leaves, stem and roots indeed was found to be independent on fruit load. The simulated dry matter distribution between tomato leaves, stem and individual clusters of fruits corresponded reasonably well to measured data from a glasshouse experiment.
Morfogenese en stofverdeling van kasgewassen in relatie tot het kasklimaat : een verkennende bijdrage voor toekomstig onderzoek
Marcelis, L.F.M. - \ 1988
Wageningen : CABO (CABO-verslag nr. 87) - 23
distributie - formatie - voedingsstoffenreserves - glastuinbouw - kasgewassen - distribution - formation - nutrient reserves - greenhouse horticulture - greenhouse crops
Dit rapport omvat een literatuurstudie naar de groei van afzonderlijke planteorganen en de verdeling van drogestof over deze organen
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