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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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    Desiccation Tolerance : Avoiding Cellular Damage during Drying and Rehydration
    Oliver, Melvin J. ; Farrant, Jill M. ; Hilhorst, Henk W.M. ; Mundree, Sagadevan ; Williams, Brett ; Bewley, J.D. - \ 2020
    Annual Review of Plant Biology 71 (2020). - ISSN 1543-5008 - p. 435 - 460.
    cellular protection - desiccation - desiccation tolerance - mechanical stress - metabolic stress - reactive oxygen species - resurrection plants - senescence

    Desiccation of plants is often lethal but is tolerated by the majority of seeds and by vegetative tissues of only a small number of land plants. Desiccation tolerance is an ancient trait, lost from vegetative tissues following the appearance of tracheids but reappearing in several lineages when selection pressures favored its evolution. Cells of all desiccation-tolerant plants and seeds must possess a core set of mechanisms to protect them from desiccation- and rehydration-induced damage. This review explores how desiccation generates cell damage and how tolerant cells assuage the complex array of mechanical, structural, metabolic, and chemical stresses and survive.Likewise, the stress of rehydration requires appropriate mitigating cellular responses. We also explore what comparative genomics, both structural and responsive, have added to our understanding of cellular protection mechanisms induced by desiccation, and how vegetative desiccation tolerance circumvents destructive, stress-induced cell senescence.

    Desiccation tolerance in seeds and plants
    Dias Costa, M.C. - \ 2016
    Wageningen University. Promotor(en): Harro Bouwmeester; Henk Hilhorst; Wilco Ligterink. - Wageningen : Wageningen University - ISBN 9789462576278 - 183
    desiccation tolerance - tolerance - plants - seeds - plant physiology - stress tolerance - drought resistance - abscisic acid - uitdrogingstolerantie - tolerantie - planten - zaden - plantenfysiologie - stresstolerantie - droogteresistentie - abscisinezuur

    The interest of research groups in desiccation tolerance (DT) has increased substantially over the last decades. The emergence of germinated orthodox seeds and resurrection plants as main research models has pushed the limits of our knowledge beyond boundaries. At the same time, new questions and new challenges were posed. The work presented in this thesis aims at shedding light on some of these questions, deepening our understanding of DT and providing relevant information to improve stress resistance in crops.

    Chapter 2 is a survey of the literature and discusses the ecological and evolutionary significance for seeds to be able to re-acquire DT after germination. This chapter also discusses recent progress in DT studies using developing and germinated seeds of the model plants Arabidopsis thaliana and Medicago truncatula.

    In Chapter 3 I used microarray data from a time series of DT re-acquisition, together with network analysis of gene expression, to gain temporal resolution and identify relevant genes involved in the re-acquisition of DT in germinated A. thaliana seeds by incubation in abscisic acid (ABA). Overall, genes related to protection, response to stresses, seed development and seed dormancy were up-regulated, whereas genes related to cell growth and photosynthesis were down-regulated with time. Genes that respond early to exogenous ABA were related to wax biosynthetic processes, lipid storage, seed development and response to ABA stimulus. Genes that respond late to exogenous ABA were related to syncytium formation and response to abiotic stimulus (mainly light stimulus). The robustness of the network was confirmed by the projection of sets of genes – related to the acquisition of DT, seed dormancy, drought responses of adult plants and re-induction of DT by polyethylene glycol – on this network.

    In Chapter 4 the relation between DT in germinated seeds and drought resistance in adult plants is analysed, using rice (Oryza sativa) as experimental model. Considering the predictions of a future with lower availability of fresh water, efforts to increase rice drought tolerance without reducing yield are increasingly important. The results presented in this chapter suggest that the intrinsic mechanisms of drought tolerance in adult plants are part of the mechanisms used by seeds to tolerate desiccation, but the molecular nature of these mechanisms remains elusive.

    Chapter 5 explores the relation between DT and longevity in germinated seeds of the Brazilian tree species Sesbania virgata as experimental model. DT and longevity are acquired by orthodox seeds during the maturation phase of development and lost upon germination. DT can be re-induced in germinated seeds by an osmotic and/or ABA treatment, but there is no information on how these treatments affect seed longevity. S. virgata seeds lose DT slowly upon radicle growth. The radicle appeared to be the most sensitive organ and the cotyledons the most resistant. The ability to produce lateral roots was key for whole seedling survival. An osmotic treatment improved DT in germinated S. virgata seeds, but not longevity. This implies that DT and seed longevity can be uncoupled.

    Xerophyta viscosa is one of the best studied resurrection species. Despite the fact that adult plants and mature seeds display DT, young X. viscosa seedlings are sensitive to fast drying. A treatment with ABA can induce DT early in shoots of these seedlings, but not in roots. Chapter 6 addresses the changes in the transcriptome and proteome of X. viscosa seedlings during induction of DT. A draft genome sequence of X. viscosa was used to improve transcript and protein identification and annotation. Differences in ABA signalling and the cross talk between ABA and ethylene were presented as determinant for shoot and root responses. Moreover, differences in the accumulation of late embryogenesis abundant proteins were also shown as being key for DT in shoots and roots.

    In Chapter 7, DT-transcriptomes of distantly related organisms are compared and surveyed for a core set of genes representing the signatures of critical adaptive DT mechanisms. A shortlist of 260 genes emerged, with a significant number of genes under the control of ABI3 and related to dormancy. The results reinforced the idea that core mechanisms and key regulators involved in DT developed early in the history of life and were carried forward by diverse species and life forms in a conserved manner and in conjunction with dormancy.

    In Chapter 8, the findings of this thesis are integrated, showing how they can contribute to future improvement of stress tolerance in crops. The ability of germinated seeds to re-acquire DT is discussed in combination with dormancy and longevity and related to seed survival under unfavourable environmental conditions. The relationship between drought- and desiccation tolerance and the role of ABA are presented briefly. Possible approaches to mine for new genes for crop improvement, such as searching for conserved genes and analysing new genome sequences, are addressed. Finally, a new perspective of the way to consider the evolution of DT is proposed.

    Dissecting the seed-to-seedling transition in Arabidopsis thaliana by gene co-expression networks
    Silva, A.T. - \ 2015
    Wageningen University. Promotor(en): Harro Bouwmeester, co-promotor(en): Henk Hilhorst; Wilco Ligterink. - Wageningen : Wageningen University - ISBN 9789462575929 - 177
    arabidopsis thaliana - zaden - zaadkieming - zaailingen - genexpressie - uitdrogingstolerantie - arabidopsis thaliana - seeds - seed germination - seedlings - gene expression - desiccation tolerance

    One of the most important developmental processes in the life-cycle of higher plants is the transition from a seed to a plant and from a generative to a vegetative developmental program. The major hallmark or end-point of the transition from seed to plant is the onset of photosynthesis and the concomitant shift from a heterotrophic to an autotrophic organism. It is advantageous for a species to keep the period of seedling establishment as short as possible since young seedlings are highly sensitive to biotic and abiotic stresses. This implies that the extreme stress tolerance of seeds to i.e. desiccation is lost upon germination. If the regulatory principles of the seed-to-seedling transition are better understood it may become feasible to maintain the seed’s stress tolerance well into the seedling stage.

    Despite the profound impact of seedling performance on crop establishment and yield, the seed-to-seedling transition has hardly been studied at the molecular level. This thesis aims at deciphering and understanding the molecular processes that govern this transition in Arabidopsis thaliana. A high-resolution study of the molecular events that occur during these successive transitional stages may provide clues as to the regulatory principles that drive this transition. It may also yield information about the factors that determine the (in)ability to revert to a developmental mode and which features are critical for the maintenance and loss of desiccation tolerance and other stress responses.

    In Chapter 1 important processes such as abscisic acid and their regulation are described and it is discussed in what way the seed-to-seedling transition may have links to a trait such as desiccation tolerance. An overview is presented of the current knowledge of the seed-to-seedling phase transition and the existence of a temporal developmental block that can be manipulated by osmotic treatment, the carbon/nitrogen balance and by abscisic acid which results in the re-establishment of desiccation tolerance.

    Chapter 2 focuses on comprehensive gene regulation by a detailed transcriptional analysis across seven developmental stages of the seed-to-seedling transition. It describes the inference of a gene co-expression network and several transcriptional modules. I show that such an approach highlights important molecular processes during seedling development, which would not likely be derived from comparative transcript profiling. Moreover, I show that a putative key regulator in one of the transcriptional modules affects late seedling establishment.

    In Chapter 3 it is shown how this phase transition is expressed in the primary metabolite profiles in correlation with gene expression. A metabolite-metabolite correlation analysis suggested two profiles, which point at the metabolic preparation of seed germination and of vigorous seedling establishment. Furthermore, a linear correlation between metabolite contents and transcript abundance (Chapter 2) provides a global view of the transcriptional and metabolic changes during the seed-to-seedling transition. It creates new perspectives of the regulatory complexes underlying the seed-to-seedling transition.

    Chapter 4 describes the development of a novel method to re-establish desiccation tolerance during the seed-to-seedling transition without adverse effects such as those caused by an osmotic treatment with polyethylene glycol. By using this method, named ‘Mild Air Drying Treatment’ (MADT), I show that the re-establishment of desiccation tolerance is not linked to a reduced ability to accumulate ABA in the desiccation sensitive seeds (germinated seeds at root hair stage). I also present a genetic interaction study of ABSCISIC ACID INSENSITIVE (ABI) genes in their germination response to ABA, and their response to the re-establishment of desiccation tolerance using the MADT. The interaction between ABI3 and ABI4, and between ABI4 and ABI5 act synergistically in the re-establishment of DT, as well as in the germination response to ABA.

    In a more in depth study in Chapter 5 I carried out an extensive transcript analysis to infer possible mechanisms of the re-establishment of desiccation tolerance using the MADT protocol. Possible mechanisms underlying the re-establishment of desiccation tolerance were inferred by employing a time-series comparison of germinated desiccation tolerant and -sensitive seeds. Early-response genes of the re-establishment of desiccation tolerance may play a role in events that promote the initial protection to dehydration stress, whereas the late-response genes may play a role in events that help seed to respond to the changes in water dynamics. Moreover, using a gene co-expression network and transcriptional module I concluded that a crosstalk between ABA-dependent and ABA-independent transcription factors regulate the re-establishment of desiccation tolerance.

    In Chapter 6 I discuss how the results presented in this thesis contribute to our knowledge of the molecular basis of the seed-to-seedling transition and the re-establishment of desiccation tolerance during its phase changes. Finally, new possibilities for further research are discussed, as well as the further use of the data sets to delineate the mechanisms underlying the seed-to-seedling transition and desiccation tolerance. Possible applications of the results for crop improvement are addressed. Thus, the generation of genetically modified plants that produce seeds with a stress tolerance that extends well into seedling stage may be feasible.

    Can frequent precipitation moderate drought impact on peatmoss carbon uptake in northern peatlands?
    Nijp, J.J. ; Limpens, J. ; Metselaar, K. ; Zee, S.E.A.T.M. van der; Berendse, F. ; Robroek, B.J.M. - \ 2015
    climate change - Sphagnum fuscum - Sphagnum balticum - Sphagnum majus - desiccation tolerance - mires - moisture stress - photosynthesis - rain variability - Sphagnum physiology - water balance
    Northern peatlands represent a large global carbon store that potentially can be destabilised by summer water table drawdown. Precipitation can moderate negative impacts of water table drawdown by rewetting peatmoss (Sphagnum spp.), the ecosystems’ key species. Yet, the frequency for such rewetting to be effective remains unknown. We experimentally assessed the importance of precipitation frequency for Sphagnum water supply and carbon uptake during a stepwise decrease in water tables in a growth chamber. CO2 exchange and the water balance were measured for intact cores of three peatmoss species (Sphagnum majus, S. balticum and S. fuscum) representative of three hydrologically distinct peatland microhabitats (hollow, lawn, hummock) and expected to differ in their water table-precipitation relationships. Precipitation contributed significantly to peatmoss water supply at deep water tables, demonstrating the importance of precipitation during drought. The ability to exploit transient resources was species-specific; S. fuscum carbon uptake increased linearly with precipitation frequency at deep water tables, whereas carbon uptake by S. balticum and S. majus was depressed at intermediate precipitation frequencies. Our results highlight an important role for precipitation on carbon uptake by peatmosses. Yet, the potential to moderate drought impact is species-specific and dependents on the temporal distribution of precipitation.
    Unravelling desiccation tolerance in germinated Arabidopsis seeds
    Maia de Oliveira, J. - \ 2014
    Wageningen University. Promotor(en): Harro Bouwmeester, co-promotor(en): Henk Hilhorst; Wilco Ligterink. - Wageningen : Wageningen University - ISBN 9789462570221 - 211
    arabidopsis - zaden - uitdrogingstolerantie - plantenfysiologie - groeiremmers - arabidopsis - seeds - desiccation tolerance - plant physiology - growth inhibitors

    How different organisms survive in the absence or under very limited amounts of water is still an open question. The aim of the research presented in this thesis is to explore the molecular basis of desiccation tolerance in seeds. We investigated the possibilities of using germinated desiccation sensitive seeds which were rescued to become tolerant again as a system to study the mechanisms involved in surviving severe dehydration. Using this experimental approach in combination with technologies to assess which genes, proteins, metabolites and metabolic pathways are important in dry seeds, we obtained insights on the mechanism of survival in the dry state. The understanding of such mechanisms can aid to the design of crop improvement strategies, long-term storage of seeds, and dry storage of other biological materials such as blood cell, tissues and vaccines.

    Species living in hars environments have low clade rank and are localized on former Laurasian continents: a case study of Willemia (Collembola)
    Prinzing, A. ; Haese, C.A. D'; Pavoine, S. ; Ponge, J.F. - \ 2014
    Journal of Biogeography 41 (2014)2. - ISSN 0305-0270 - p. 353 - 365.
    general-purpose genotype - niche conservatism - phylogenetic perspective - desiccation tolerance - evolutionary dynamics - cretaceous collembola - drought acclimation - diversity gradient - biological traits - extinction
    Aim Certain species have few living relatives (i.e. they occupy low clade ranks) and hence they possess high conservation value and scientific interest as unique representatives of ancient lineages. However, we do not know whether particular environments favour the maintenance of low clade ranks or whether the distribution of environments across the globe affects the global distribution of clade ranks and, hence, evolutionary uniqueness. In this study, we tested whether and how harsh environments decrease the clade ranks of the species that inhabit them. Location: Global. Methods We described the phylogeny of the collembolan genus Willemia by a parsimonious method based on 52 morphological characters and estimated the species’ use of harsh environments (polar, high mountain, desert, polluted, waterlogged, saline and acidic) from 248 publications. Results: We found that the use of different types of harsh environments is maintained among close relatives and has similar phylogenetic signals (except for the use of salinity). The use of harsh environments might therefore affect the diversification of lineages. Correcting for the phylogenetic non-independence of species, we found that species using harsh environments have comparatively low clade ranks. We also found that species using harsh environments occur almost exclusively on former Laurasian continents and that, as a statistical consequence, Laurasian species tend to have lower clade ranks. Main conclusions: We suggest that harsh environments maintain low-claderank species by decreasing, simultaneoulsy or successively, extinction and speciation, which may eventually explain the major variation in clade rank across the globe. Keywords Abiotic stress, diversification, habitat, Laurasia, niche conservatism, phylogenetic reconstruction, phylogenetic GLS analysis, phylogenetic principal components, root-skewness test, springtails.
    Dehydration and thermal inactivation of Lactobacillus plantarum WCFS1: Comparing single droplet drying to spray and freeze drying
    Perdana, J.A. ; Bereschenko, L.A. ; Fox, M.B. ; Kuperus, J.H. ; Kleerebezem, M. ; Boom, R.M. ; Schutyser, M.A.I. - \ 2013
    Food Research International 54 (2013)2. - ISSN 0963-9969 - p. 1351 - 1359.
    desiccation tolerance - phase-transitions - probiotics - temperature - membranes - vitrification - survival - bacteria - injury - cells
    We demonstrated that viability loss during single droplet drying can be explained by the sum of dehydration and thermal inactivation. For Lactobacillus plantarum WCFS1, dehydration inactivation predominantly occurred at drying temperatures below 45 °C and only depended on the moisture content. Above 45 °C the inactivation was due to a combination of dehydration and thermal inactivation, which depended on the moisture content, temperature, and drying time. A Weibull model was successfully applied to describe the thermal and dehydration inactivation and enabled the prediction of residual viability of L. plantarum WCFS1 after single droplet drying. Subsequently, the model was evaluated to predict the viability loss during laboratory scale spray drying, showing a remarkable agreement if assumed that only thermal inactivation occurred. This indicated that very high drying rates in laboratory scale spray drying could induce instant fixation of the cell suspensions in a vitrified matrix and thereby preventing dehydration inactivation. Finally, the influence of drying rate on remaining viability was evaluated by comparing single droplet drying, freeze drying and laboratory scale spray drying of the same bacterial suspension. It was shown that slow drying leads to large dehydration inactivation, which diminished in fast drying processes such as laboratory scale spray drying where thermal inactivation appears to be the predominant mechanism of inactivation.
    Functional studies of soybean (Glycine max L.) seed LEA proteins GmPM6, GmPM11, and GmPM30 by CD and FTIR spectroscopy
    Hoekstra, F.A. - \ 2012
    Plant Science 196 (2012). - ISSN 0168-9452 - p. 152 - 159.
    embryogenesis-abundant protein - desiccation tolerance - arabidopsis-thaliana - secondary structure - saccharomyces-cerevisiae - circular-dichroism - wheat-germ - dehydration - expression - plants
    The protein and mRNA levels of late embryogenesis abundant (LEA) genes may be linked to osmotic stresses. Here, we characterized three soybean hydrophilic LEA proteins – GmPM11 (LEA I), GmPM6 (LEA II), and GmPM30 (LEA III) – by circular dichroism and Fourier transform infrared spectroscopy. Structural analysis revealed that the LEA proteins adopted high amounts of disordered conformations in solution and underwent conformational changes with hydrophobicity and desiccation induction. Macromolecular interaction studies revealed that the GmPM proteins interact with non-reducing sugars and phospholipids. GmPM6 and GmPM30 but not GmPM11 could prevent beta-aggregation of poly-l-lysine after slow drying. We discuss the possible functions of hydrophilic LEA proteins in maturing seeds.
    Seed maturation in Arabidopsis is characterised by nuclear size reduction and increased chromatin condensation
    Zanten, M. van; Koini, M.A. ; Geyer, R. ; Liu, Y. ; Brambilla, V. ; Bartels, D. ; Koornneef, M. ; Fransz, P. ; Soppe, W.J.J. - \ 2011
    Proceedings of the National Academy of Sciences of the United States of America 108 (2011)50. - ISSN 0027-8424 - p. 20219 - 20224.
    plant craterostigma-plantagineum - desiccation tolerance - gene-regulation - dormancy - germination - heterochromatin - mutants - establishment - transcription - organization
    Most plant species rely on seeds for their dispersal and survival under unfavorable environmental conditions. Seeds are characterized by their low moisture content and significantly reduced metabolic activities. During the maturation phase, seeds accumulate storage reserves and become desiccation-tolerant and dormant. Growth is resumed after release of dormancy and the occurrence of favorable environmental conditions. Here we show that embryonic cotyledon nuclei of Arabidopsis thaliana seeds have a significantly reduced nuclear size, which is established at the beginning of seed maturation. In addition, the chromatin of embryonic cotyledon nuclei from mature seeds is highly condensed. Nuclei regain their size and chromatin condensation level during germination. The reduction in nuclear size is controlled by the seed maturation regulator ABSCISIC ACID-INSENSITIVE 3, and the increase during germination requires two predicted nuclear matrix proteins, LITTLE NUCLEI 1 and LITTLE NUCLEI 2. Our results suggest that the specific properties of nuclei in ripe seeds are an adaptation to desiccation, independent of dormancy. We conclude that the changes in nuclear size and chromatin condensation in seeds are independent, developmentally controlled processes
    OsLEA1a, a New Em-Like Protein of Cereal Plants
    Shih, M.D. ; Huang, L.T. ; Wei, F.J. ; Wu, M.T. ; Hoekstra, F.A. ; Hsing, Y.I.C. - \ 2010
    Plant and Cell Physiology 51 (2010)12. - ISSN 0032-0781 - p. 2132 - 2144.
    embryogenesis-abundant protein - shrimp artemia-franciscana - abscisic-acid-response - lea messenger-rnas - gene-expression - seed maturation - desiccation tolerance - arabidopsis-thaliana - secondary structure - circular-dichroism
    Proteins abundant in seeds during the late stages of development, late embryogenesis abundant (LEA) proteins, are associated with desiccation tolerance. More than 100 of the group I LEA genes, also termed Em genes, have been identified from plants, bacteria and animals. The wide distribution indicates the functional importance of these genes. In the present study, we characterized a novel Em-like gene, OsLEA1a of rice (Oryza sativa). The encoded OsLEA1a protein has an N-terminal sequence similar to that of other plant Em proteins but lacks a 20-mer motif that is the most significant feature of typical Em proteins. The location of the sole intron indicates that the second exon of OsLEA1a is the mutated product of a typical Em gene. Transcriptome analysis revealed OsLEA1a mainly expressed in embryos, with no or only a few transcripts in osmotic stress-treated vegetative tissues. Structural analysis revealed that the OsLEA1a protein adopts high amounts of disordered conformations in solution and undergoes desiccation-induced conformational changes. Macromolecular interaction studies revealed that OsLEA1a protein interacts with non-reducing sugars and phospholipids but not poly-L-lysine. Thus, although the OsLEA1a protein lost its 20-mer motif, it is still involved in the formation of bioglasses with non-reducing sugars or plasma membrane. However, the protein does not function as a chaperone as do other groups of hydrophilic LEA proteins. The orthologs of the OsLEA1a gene had been indentified from various grasses but not in dicot plants. Genetic analysis indicated that rice OsLEA1a locates at a 193 kb segment in chromosome 1 and is conserved in several published cereal genomes. Thus, the ancestor of Em-like genes might have evolved after the divergence of monocot plants.
    Characterization of Two Soybean (Clycine max. L) LEA IV Proteins by Circular Dichroism and Fourier Transform Infrared Spectrometry
    Shih, M.D. ; Hsieh, T.Y. ; Lin, T.P. ; Hsing, Y.I. ; Hoekstra, F.A. - \ 2010
    Plant and Cell Physiology 51 (2010)3. - ISSN 0032-0781 - p. 395 - 407.
    embryogenesis-abundant protein - desiccation tolerance - arabidopsis-thaliana - nucleotide-sequence - secondary structure - plant desiccation - abscisic-acid - alpha-helix - dry state - gene
    Late embryogenesis-abundant (LEA) proteins, accumulating to a high level during the late stages of seed development, may play a role as osmoprotectants. However, the functions and mechanisms of LEA proteins remained to be elucidated. Five major groups of LEA proteins have been described. In the present study, we report on the characterization of two members of soybean LEA IV proteins, basic GmPM1 and acidic GmPM28, by circular dichroism and Fourier transform infrared spectroscopy. The spectra of both proteins revealed limited defined secondary structures in the fully hydrated state. Thus, the soybean LEA IV proteins are members of ‘natively unfolded proteins’. GmPM1 or GmPM28 proteins showed a conformational change under hydrophobic or dry conditions. After fast or slow drying, the two proteins showed slightly increased proportions of defined secondary structures (a-helix and ß-sheet), from 30 to 49% and from 34 to 42% for GmPM1 and GmPm28, respectively. In the dehydrated state, GmPM1 and GmPM28 interact with non-reducing sugars to improve the transition temperature of cellular glass, with poly-l-lysine to prevent dehydration-induced aggregation and with phospholipids to maintain the liquid crystal phase over a wide temperature range. Our work suggests that soybean LEA IV proteins are functional in the dry state. They are one of the important components in cellular glasses and may stabilize desiccation-sensitive proteins and plasma membranes during dehydration
    Natural modifiers of seed longevity in the Arabidopsis mutants abscisic acid insensitive3-5 (abi3-5) and leafy cotyledon1-3 (lec1-3)
    Sugliani, M.R.L. ; Rajjou, L. ; Clerkx, E.J.M. ; Koornneef, M. ; Soppe, W.J.J. - \ 2009
    New Phytologist 184 (2009)4. - ISSN 0028-646X - p. 898 - 908.
    heat-shock proteins - desiccation tolerance - genetic-variation - allelic variation - leafy cotyledon1 - germination - maturation - thaliana - expression - networks
    • Seed longevity is an important trait in many crops and is essential for the success of most land plant species. Current knowledge of its molecular regulation is limited. The Arabidopsis mutants abscisic acid insensitive3-5 (abi3-5) and leafy cotyledon1-3 (lec1-3) have impaired seed maturation and quickly lose seed viability. abi3-5 and lec1-3 were used as sensitized genetic backgrounds for the study of seed longevity. • We exploited the natural variation of Arabidopsis to create introgression lines from the Seis am Schlern and Shahdara accessions in, respectively, the abi3-5 and lec1-3 backgrounds. These lines carry natural modifiers of the abi3 and lec1 phenotypes. Longevity tests and a proteomic analysis were conducted to describe the seed physiology of each line. • The modifier lines showed improved seed longevity. The Shahdara modifiers can partially re-establish the seed developmental programs controlled by LEC1 and restore the accumulation of seed storage proteins that are reduced in abi3-5 and lec1-3. • The isolation and characterization of natural modifiers of the seed maturation mutants abi3-5 and lec1-3, and the analysis of their seed proteomes, advance our current understanding of seed longevity
    Morphophysiological development of Tabeluia serratifolia Vahl Nich. seeds
    Carvalho, M.L. ; Nery, M.C. ; Oliveira, L.M. ; Hilhorst, H.W.M. ; Guimaraes, R.M. - \ 2008
    Scientia agricola 65 (2008)6. - ISSN 0103-9016 - p. 643 - 651.
    desiccation tolerance - maturation - proteins - storage - maize - oligosaccharides - quality - sucrose - vigor
    Tabebuia serratifolia is used for the reforestation of degraded areas. Despite protection by law for permanent preservation, the species is in danger of extinction due to improper exploitation. With the objective to aid preservation and long term storage of the species we evaluated morphophysiological alterations of T. serratifolia seeds during the maturation process in order to identify markers that can be used for harvesting and storage. Fruits were collected at anthesis and seven developmental stages from trees growing in Lavras, state of Minas Gerais, Brazil. At each harvest, fruits and seeds were evaluated for color and size, moisture content, dry matter, internal morphology (by X-ray analysis), germination parameters (in vitro and ex vitro), as well as sugar and polyphenol content and heat resistant proteins. During the maturation process the initially green fruits changed to a brownish color and grew from a length of 7 to 18 cm; cracks appeared at the beginning of seed dispersal. The seed color varied from leaf-green to brownish and the length from 1 to 3 cm. The first indicatior of physiological maturity should be observed at 39 days post-anthesis, when variations the color and size of both fruits and seeds were observed. Increase in the moisture content, dry matter and germination, percentage of seeds and embryos in vitro, as well as a reduction in sugar content and LEA proteins were also observed. The physiological maturity of T. serratifolia seeds was reached 53 days after anthesis, coinciding with a maximum of dry matter accumulation and germination (and index of germination speed ex vitro), decrease in phenol levels, higher intensity of heat-resistant protein bands and the beginning of fruit opening.
    Mechanism of endocarp-imposed constraints of germination of Lannea microcarpa seeds
    Neya, O. ; Hoekstra, F.A. ; Golovina, E.A. - \ 2008
    Seed Science Research 18 (2008)01. - ISSN 0960-2585 - p. 13 - 24.
    rhus species anacardiaceae - physical dormancy - ftir microspectroscopy - desiccation tolerance - ethylene - spectroscopy - metabolism - embryos - sativa
    Lannea microcarpa, a multipurpose tree species from the dry African savanna, sheds seeds that often display inhibition of germination. The underlying mechanism was investigated using seeds processed from fully matured fruits collected from natural stands in Burkina Faso. Germination of fresh seeds was variable (16¿28%), while they did not germinate after drying and rehydration. Mechanical scarification of the endocarp at the proximal end of the seeds increased germination to 83¿94%. Scarification on the distal end led to delayed radicle emergence through the produced hole in c. 40% of the seeds. The endocarp was permeable to water and respiratory gases. Increased water content in scarified seeds was associated with radicle extension during germination. Intact and scarified non-germinated seeds displayed a moderate rate of respiration with respiratory quotient (RQ) values of c. 1. Respiration increased and RQ decreased to c. 0.7 with radicle emergence. Ethylene evolution peaked in both intact and scarified seeds at the beginning of incubation and then decreased to low values. Inhibition of ethylene production by 1¿5 mM 2-amino-ethoxyvinylglycine (AVG) caused only a partial decrease of germination of the scarified seeds. Intact non-germinated seeds gradually lost viability during incubation at 30°C, but could be rescued by delayed scarification before day 15 of incubation. It is concluded that radicle emergence in dry L. microcarpa seeds is inhibited only mechanically. The mechanical properties of the endocarp are attributed to irreversible structural changes of the lignin¿hemicellulose complex, which occur during drying.
    Desiccation tolerance and sensitivity in Medicago truncatula and Inga vera seeds
    Faria, J.M.R. - \ 2006
    Wageningen University. Promotor(en): Anne Mie Emons; Linus van der Plas, co-promotor(en): Henk Hilhorst; Andre van Lammeren. - Wageningen : - ISBN 9789085044178 - 135
    zaden - medicago truncatula - inga - uitdrogingstolerantie - zaadlevensduur - celcyclus - verdroging - opslag - plantenfysiologie - plantenontwikkeling - seeds - medicago truncatula - inga - desiccation tolerance - seed longevity - cell cycle - desiccation - storage - plant physiology - plant development
    Orthodox seeds acquire desiccation tolerance (DT) during their development which enables them to pass through the phase of maturation drying by the end of their development and enter a state of quiescence. After harvesting, these seeds can be dried further and stored for the long-term without significant loss of viability. On the other hand, there are many species that produce recalcitrant seeds, which have a developmental history and post-harvest behaviour rather opposite from the orthodox types. These are shed with high moisture contents (MCs), are metabolically active and can not be dried to MCs low enough to allow safe storage. Recalcitrant seeds thus represent a big challenge to those who need to store them in seed banks for germplasm conservation purposes. In order to gain insight into the recalcitrance phenomenon, this thesis addresses questions concerning the physiological, cytological and molecular aspects of desiccation sensitivity in developing and mature recalcitrant seeds of the tree species Inga vera Willd. subsp. affinis and in mature and germinating orthodox seeds of the model species Medicago truncatula Gaertn. cv. Jemalong A17.

    The desiccation sensitivity of I.vera seeds was analyzed in terms of water relations, DNA content and the microtubular cytoskeleton. Developing (6, 9 and 10 weeks after flowering - WAF) and mature seeds (14 WAF) were collected and processed, ending up with the naked embryos. Slight desiccation of immature embryos increased germination, but further drying resulted in a quick decline of germinability. Total loss of viability occurred while the embryos still showed high MCs (around 0.4 g H/g dry matter) and high water activity (a w ), around 0.88, irrespective of the developmental stage. During development the desiccation sensitivity of the embryos decreased slightly, while the percentage of cells with 4C DNA remained constant, around 15% in the root and 10% in the shoot, suggesting no relation between DT and DNA content. Immuno-histochemical detection of microtubules (MTs) in embryonic axes cells ofmature embryos showed abundant cortical microtubule arrays, which were not affected by mild desiccation, but were totally dismantled by further drying. Upon rehydration, damaged cells were not able to reconstitute the microtubular cytoskeleton and this might be related to the viability loss during dehydration of the embryo.

    The desiccation sensitivity was also studied in seeds of M. truncatula during and after germination. When seedlings with a radicle length as short as 1 mm were dried back to the original MC found in dry seeds and rehydrated, only 15% survived. Seedlings with a radicle length equal or longer than 2 mm did not survive dehydration at all. By subjecting seedlings to an osmotic treatment with polyethylene glycol - PEG (-1.8 MPa) before drying, DT could be re-established in seedlings with a radicle length up to 2 mm. Flow cytometric analyses and MT visualisation in radicle cells of growing M. truncatula seedlings showed that up to a radicle length of 2 mm, the cell cycle had not been resumed, as shown by the absence of DNA synthesis and cell division, which were first detected in 3 mm long radicles. Therefore DT could be re-established only before the resumption of the cell cycle in the radicles. Dehydration of seedlings with a 2 mm protruded radicle, with or without previous PEG treatment, caused disassembly of MTs. Upon rehydration MTs were not reassembled in radicle cells of untreated seedlings, while PEG-treated seedlings were able to reconstitute the microtubular cytoskeleton and develop into normal seedlings. Dehydration of untreated seedlings with a 2 mm protruded radicle also led to an apoptotic-like DNA fragmentation in radicle cells, while in PEG-treated seedlings DNA integrity was maintained. The results showed that for different cellular components, desiccation-tolerant seedlings may apply distinct strategies to survive dehydration, either by further repair or avoidance of the damages.

    This thesis also investigated the changes in the expression ofvarious genes related to seed development, DT, cell cycle and cytoskeleton during loss and re-establishment of DT in germinating seeds and in seedlings of M. truncatula. The transcript levels of the studied genes in radicle cells were relatively quantified by real time PCR, using specific primers for M. truncatula. Clear changes in transcript abundance were detected during and after germination and in response to osmotic treatment and dehydration. DT-related genes ( EM6 , PER1 and sHSP18.2 ) were down regulated during germination and up regulated by osmotic treatment, which correlated with the loss and re-acquisition of DT in the radicles. The expression pattern of the developmental gene ABI3 was similar to that of the stress related genes, corresponding with a possible control of the stress response by this gene. Abundance of LEC1 transcript correlated more with the germination process than with osmotic stress. The cytoskeleton genes ( ACT and TUB ) were up-regulated during germination, not affected substantially by osmotic treatment and down-regulated by subsequent dehydration, which was related with the massive breakdown of the cytoskeleton upon dehydration of seedlings. Expression of CDC2a , one of the key regulators of the G 1 -to-S transition, was clearly associated with the occurrence of the first cell cycle in the growing radicle. Radicles that have gone through the first cell cycle (3 mm long) may respond to osmoticum in a similar fashion as desiccation tolerant radicles, in terms of gene regulation. However, the resumption of the cell cycle appears to be an overriding factor that abolishes re-establishment of DT.  

    Recalcitrant seeds are metabolically active in storage and this leads to a short longevity. I.vera embryos are among the worst storable species known, retaining viability for not much longer than one or two weeks if stored in semi-permeable bags at 20 or 5 o C, respectively. Thus, an attempt was made to slow down the metabolism of I.vera embryos and, consequently, prolong their short storability. For this, embryos were stored in an osmotic medium (PEG at -1.7 MPa) with or without the addition of ABA, a well known germination inhibitor. Besides slowing down the metabolism, osmotic stress and ABA can lead to the expression of genes involved in DT in plants or seeds. Storage in PEG was capable of keeping the germination rate of I.vera embryos at 100% until 30 days, either at 5 or 20 o C, thus causing a three-fold increase in storability, when compared to the embryos stored in semi-permeable bags. Starch content, as major food reserve, generally decreased with increasing storage duration. However, we found no direct relationship between starch content and viability/germination. The effect of ABA showed to be temperature-dependent, being positive at 20 o C and negative at 5 o C. The permanence of the embryos in PEG for 14 days did not render them more tolerant to desiccation. Another technique applied in order to prolong the storability was sealed storage of partially dried embryos. In this case, storability was better than the control, but not as long as in the PEG storage. Anyway, both approaches used in this thesis seem to be promising to prolong the naturally short storability of recalcitrant seeds.

    We hypothesize that mature recalcitrant seeds have completely lost unique seed traits such as DT and should therefore be regarded as vegetatively growing seedlings/plants rather than seeds and, hence, storage under controlled atmosphere may prove successful. This type of storage is common in long term conservation of fresh fruits and vegetables.
    PCIB an antiauxin enhances microspore embryogenisis in microspore culture of Brassica juncea
    Agarwal, P.K. ; Agarwal, P. ; Custers, J.B.M. ; Liu, C.M. ; Bhojwani, S.S. - \ 2006
    Plant Cell, Tissue and Organ Culture: an international journal on in vitro culture of higher plants 86 (2006)2. - ISSN 0167-6857 - p. 201 - 210.
    doubled haploid plants - immediate colchicine treatment - napus cv topas - oilseed rape - desiccation tolerance - efficient production - anther cultures - heat-shock - embryos - induction
    An efficient protocol to improve microspore embryogenesis is established in an important oleiferous crop, Brassica juncea (Indian mustard). Colchicine was used for enhancing microspore embryogenesis and also to obtain doubled haploid embryos. Colchicine at high concentrations (>10 mg l¿1), for 24 h, proved convenient for direct recovery of diploid embryos. Higher temperature treatment and an antiauxin PCIB (p-chlorophenoxyisobutyric acid) enhanced microspore embryogenesis significantly as compared to colchicine. An increase in temperature from 32°C to 35°C proved very efficient in increasing embryogenesis by 10-fold. The highest embryogenesis rate was obtained when PCIB was added at 35°C in the culture after 1 day of culture initiation. 20 ¿M PCIB could enhance microspore embryogenesis by 5-fold. Different abnormal shapes of embryos like lemon, banana, flask and fused cotyledons were observed. Both normal and fused cotyledonous embryos showed normal germination when transferred on the B5 basal medium
    Changes in DNa and microtubules during loss and re-establishment of desiccation tolerance in germinating Medicago truncatula seeds
    Faria, J.M.R. ; Buitink, J. ; Lammeren, A.A.M. van; Hilhorst, H.W.M. - \ 2005
    Journal of Experimental Botany 56 (2005)418. - ISSN 0022-0957 - p. 2119 - 2130.
    celcyclus - uitdrogingstolerantie - dna - medicago truncatula - microtubuli - cell cycle - desiccation tolerance - dna - medicago truncatula - microtubules - nuclear replication activity - programmed cell-death - hydration-dehydration - recalcitrant seeds - plant-cells - fragmentation - localization - integrity - radicles - survival
    Desiccation tolerance (DT) in orthodox seeds is acquired during seed development and lost upon imbibition/germination, purportedly upon the resumption of DNA synthesis in the radicle cells. In the present study, flow cytometric analyses and visualization of microtubules (MTs) in radicle cells of seedlings of Medicago truncatula showed that up to a radicle length of 2 mm, there is neither DNA synthesis nor cell division, which were first detected in radicles with a length of 3 mm. However, DT started to be lost well before the resumption of DNA synthesis, when germinating seeds were dried back. By applying an osmotic treatment with polyethylene glycol (PEG) before dehydration, it was possible to re-establish DT in seedlings with a radicle up to 2 mm long. Dehydration of seedlings with a 2 mm radicle, with or without PEG treatment, caused disassembly of MTs and appearance of tubulin granules. Subsequent pre-humidification led to an almost complete disappearance of both MTs and tubulin granules. Upon rehydration, neither MTs nor tubulin granules were detected in radicle cells of untreated seedlings, while PEG-treated seedlings were able to reconstitute the microtubular cytoskeleton and continue their normal development. Dehydration of untreated seedlings also led to an apoptotic-like DNA fragmentation in radicle cells, while in PEG-treated seedlingss DNA integrity was maintained. The results showed that for different cellular components, desiccation-tolerant seedlings may apply distinct strategies to survive dehydration, either by avoidance or further repair of the damages
    Survival and vigour of ultra-dry seeds after ten years of hermetic storage
    Hong, T.D. ; Ellis, R.H. ; Astley, D. ; Pinnegar, A.E. ; Groot, S.P.C. ; Kraak, H.L. - \ 2005
    Seed Science and Technology 33 (2005)2. - ISSN 0251-0952 - p. 449 - 460.
    zaadkieming - groeikracht - uitdrogingstolerantie - daucus carota - aardnoten - koolzaad - allium cepa - opslag van zaden - seed germination - vigour - desiccation tolerance - daucus carota - groundnuts - rape - allium cepa - seed storage - moisture-content limit - logarithmic relation - theoretical basis - longevity - temperatures - groundnut - protocols - lettuce
    Seeds of carrot, groundnut, lettuce, oilseed rape and onion were stored hermetically in laminated aluminium foil packets in four environments (dry or ultra-dry moisture contents combined factorially with temperatures of 20 degrees C or -20 degrees C), replicated at several sites. After ten years' hermetic storage, seed moisture content, equilibrium relative humidity, viability (assessed by ability to germinate normally in standard germination tests) and vigour were determined. After a decade, the change in seed moisture content of samples stored at -20 degrees C was small or nil. Except for groundnut and lettuce (where loss in viability was about 8 and 3%, respectively), no loss in viability was detected after 10 years' hermetic storage at -20 degrees C. In all cases, there was no difference in seed survival between moisture contents at this temperature (P > 0.25). Comparison of seed vigour (root length and rate of germination) also confirmed that drying to moisture contents in equilibrium with 10-12% r.h. had no detrimental effect to longevity when stored at -20 degrees C: the only significant (P <0.05) differences detected were slightly greater root lengths for ultra-dry storage of four of the six seed lots. Seed moisture content had increased after a decade at 20 degrees C (generally to the level in equilibrium with ambient relative humidity). Hence, sub-zero temperature storage helped maintain the long-term integrity of the laminated aluminium foil packets, as well as that of the seeds within.
    Alternatieven voor tuinturf bij droogverkoop van bollen en vasteplanten
    Groen, N.P.A. ; Gude, H. - \ 2004
    Lisse : PPO Bloembollen - 29
    bloembollen - verpakken - uitdrogingstolerantie - turf - handel - landbouwkundig onderzoek - nederland - ornamental bulbs - packing - desiccation tolerance - peat - trade - agricultural research - netherlands
    Een aantal bloembollen en vaste planten drogen zonder goede beschering tijdens de verkoopfase te veel uit waardoor de groei kan stagneren. Ook beschadiging moet worden voorkomen, evenals condensvorming. Op dit moment wordt voornamelijk tuinturf of houtmot in een plastic verpakking gebruikt. De beschikbaarheid van goede tuinturf wordt steeds minder. Een uitgebreide literatuurstudie is uitgevoerd naar mogelijke vervangers van tuinturf of houtmot als verpakkinsmateriaal bij de droogverkoop van bloembollen. Het doel van dit literatuuroverzicht is handvatten aan te reiken ter vervanging van tuinturf of houtmot en ter verbetering van de kwaliteit van bollen of vaste planten in de verkoopfase.
    Genetic differences in seed longevity of various Arabidopsis mutants
    Clerkx, E.J.M. ; Vries, M.H.C. de; Ruijs, G.J. ; Groot, S.P.C. ; Koornneef, M. - \ 2004
    Physiologia Plantarum 121 (2004)3. - ISSN 0031-9317 - p. 448 - 461.
    thaliana l heynh - desiccation tolerance - abscisic-acid - superoxide-dismutase - sunflower seeds - glutathione-deficient - lipid-peroxidation - oxidative damage - moisture-content - germination
    Seeds gradually lose their viability during dry storage. The damage that occurs at the biochemical level can alter the seed physiological status and is affected by the storage conditions of the seeds. Although these environmental conditions controlling loss of viability have been investigated frequently, little information is available on the genetics of seed longevity. Using Arabidopsis mutants in defined developmental or biochemical pathways such as those affected in seed coat composition, seed dormancy, hormone function and control of oxidative stress, we tried to gain insight into the genes and mechanisms controlling viability of stored seeds. Mutations like abscisic acid insensitive3 (abi3) as well as abscisic acid deficient1 (aba1) show reduced longevity, which may be partially related to the seed dormancy phenotype of these mutants. Mutants with seed coat alterations, especially aberrant tests shape (ats), showed a stronger reduction in germination percentage after storage, indicating the importance of a 'functional' seed coat for seed longevity. A specific emphasis was placed on mutants affected in dealing with Reactive Oxygen Species (ROS). Because several pathways are involved in protection against ROS and because gene redundancy is a common feature in Arabidopsis, 'double' mutants were generated. These 'double' mutants and the corresponding single mutants were subjected to a controlled deterioration test (CDT) and a germination assay on hydrogen peroxide (H2O2) after prolonged storage at two relative humidities. CDT and germination on H2O2 affected all genotypes, although it appears that other effects like genetic background are more important than the deficiencies in the ROS scavenging pathway. Explanations for this limited effect of mutations affecting ROS scavenging are discussed
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