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Background and Aims Sclerotinia sclerotiorum can attack >400 plant species worldwide. Very few studies have investigated host–pathogen interactions at the plant surface and cellular level in resistant genotypes of oilseed rape/canola (Brassica napus). Methods Infection processes of S. sclerotiorum were examined on two B. napus genotypes, one resistant cultivar ‘Charlton’ and one susceptible ‘RQ001-02M2’ by light and scanning electron microscopy from 2 h to 8 d post-inoculation (dpi). Key Results The resistant ‘Charlton’ impeded fungal growth at 1, 2 and 3 dpi, suppressed formation of appresoria and infection cushions, caused extrusion of protoplast from hyphal cells and produced a hypersensitive reaction. At 8 dpi, whilst in ‘Charlton’ pathogen invasion was mainly confined to the upper epidermis, in the susceptible ‘RQ001-02M2’, colonization up to the spongy mesophyll cells was evident. Calcium oxalate crystals were found in the upper epidermis and in palisade cells in susceptible ‘RQ001-02M2’ at 6 dpi, and throughout leaf tissues at 8 dpi. In resistant ‘Charlton’, crystals were not observed at 6 dpi, whereas at 8 dpi they were mainly confined to the upper epidermis. Starch deposits were also more prevalent in ‘RQ001-02M2’. Conclusions This study demonstrates for the first time at the cellular level that resistance to S. sclerotiorum in B. napus is a result of retardation of pathogen development, both on the plant surface and within host tissues. The resistance mechanisms identified in this study will be useful for engineering disease-resistant genotypes and for developing markers for screening for resistance against this pathogen. [ABSTRACT FROM AUTHOR]

Background and Aims: Using two parental clones of outcrossing Trifolium ambiguum as a potential model system, we examined how during seed development the maternal parent, number of seeds per pod, seed position within the pod, and pod position within the inflorescence influenced individual seed fresh weight, dry weight, water content, germinability, desiccation tolerance, hardseededness, and subsequent longevity of individual seeds. [ABSTRACT FROM PUBLISHER]

Background and Aims: Recent phylogenetic analysis has placed the aquatic family Hydatellaceae as an early-divergent angiosperm. Understanding seed dormancy, germination and desiccation tolerance of Hydatellaceae will facilitate ex situ conservation and advance hypotheses regarding angiosperm evolution. [ABSTRACT FROM PUBLISHER]

Background and Aims: The smoke-derived compound karrikinolide (KAR1) shows significant potential as a trigger for the synchronous germination of seeds in a variety of plant-management contexts, from weed seeds in paddocks, to native seeds when restoring degraded lands. Understanding how KAR1 interacts with seed physiology is a necessary precursor to the development of the compound as an efficient and effective management tool. This study tested the ability of KAR1 to stimulate germination of seeds of the global agronomic weed Brassica tournefortii, at different hydration states, to gain insight into how the timing of KAR1 applications in the field should be managed relative to rain events. [ABSTRACT FROM PUBLISHER]

Background: Conservation through reserves alone is now considered unlikely to achieve protection of plant species necessary to mitigate direct losses of habitat and the pervasive impact of global climate change. Assisted translocation/migration represent new challenges in the face of climate change; species, particularly orchids, will need artificial assistance to migrate from hostile environments, across ecological barriers (alienated lands such as farmlands and built infrastructure) to new climatically buffered sites. The technology and science to underpin assisted migration concepts are in their infancy for plants in general, and orchids, with their high degree of rarity, represent a particularly challenging group for which these principles need to be developed. It is likely that orchids, more than any other plant family, will be in the front-line of species to suffer large-scale extinction events as a result of climate change. [ABSTRACT FROM PUBLISHER]

Background and Aims In neotropical forests, very small-seeded pioneer species ( Methods For 14 neotropical pioneer species, the hypothesis is tested that small-seeded species, with shallow initial rooting depths, reduce the risks associated with desiccation by germinating more slowly and at higher water potentials than large-seeded species. Key Results Germination occurred both more quickly and at lower water potentials with increasing seed mass. For example, Ochroma pyramidale (seed mass 5·5 mg) had a time to 50 % germination (T50) of 2·8 d and a median base potential for germination (ψb50) of −1·8 MPa while Clidemia quinquenervia (seed mass 0·017 mg) had a T50 of 17·6 d and ψb50 of −1·1 MPa. Conclusions These data suggest that small-seeded species germinate only in comparatively moist microsites, such as small canopy gaps, which may reduce the risk of drought-induced mortality. Conversely, large-seeded species are able to germinate in the drier environment of large gaps, where they benefit by enhanced seedling growth in a high irradiance environment. The positive association of seed size and canopy gap size for optimal seedling establishment is maintained by differential germination responses to soil water availability coupled with the scaling of radicle growth rate and seed size, which collectively confer greater drought tolerance on large-seeded species. [ABSTRACT FROM AUTHOR]

Background and Aims: Ecotypic differentiation has been explored in numerous plant species, but has been largely ignored in the Orchidaceae. Applying a specific germination protocol for widespread seed sources may be unreliable due to inherent physiological or genetic differences in localized populations. It is crucial to determine whether ecotypic differentiation exists for restoration and conservation programmes. Calopogon tuberosus var. tuberosus, a widespread terrestrial orchid of eastern North America, is a model species to explore ecotypic differences in germination requirements, as this species occupies diverse habitats spanning a wide geographical range. [ABSTRACT FROM PUBLISHER]

Background and Aims: Repair of damage to DNA of seed embryos sustained during long periods of quiescence under dry desert conditions is important for subsequent germination. The possibility that repair of embryo DNA can be facilitated by small amounts of water derived from dew temporarily captured at night by pectinaceous surface pellicles was tested. These pellicles are secreted during early seed development and form mucilage when hydrated. [ABSTRACT FROM PUBLISHER]

• Background and Aims Seedlings of Acanthocarpus preissii are needed for coastal sand dune restoration in Western Australia. However, seeds of this Western Australian endemic have proven to be very difficult to germinate. The aims of this study were to define a dormancy-breaking protocol, identify time of suitable conditions for dormancy-break in the field and classify the type of seed dormancy in this species. [ABSTRACT FROM PUBLISHER]

• Background. Two families of proteins that transport small peptides, the oligopeptide transporters (OPTs) and the peptide transporters (PTRs), have been recognized in eukaryotes. Higher plants contain a far greater number of genes for these transporters than do other eukaryotes. This may be indicative of the relative importance of (oligo)peptides and their transport to plant growth and metabolism.• Recent progress. Recent studies are now allowing us to assign functions to these transporters and are starting to identify their in-planta substrates, revealing unexpected and important contributions of the transporters to plant growth and developmental processes. This Botanical Briefing appraises recent findings that PTRs and OPTs have key roles to play in the control of plant cell growth and development. Evidence is presented that some of these transporters have functions outside that of nitrogen nutrition and that these carriers can also surprise us with their totally unexpected choice of substrates. [ABSTRACT FROM AUTHOR]

• Background and Aims Moss food-conducting cells (leptoids and specialized parenchyma cells) have a highly distinctive cytology characterized by a polarized cytoplasmic organization and longitudinal alignment of plastids, mitochondria, endoplasmic reticulum and vesicles along endoplasmic microtubules. Previous studies on the desiccation biology of mosses have focused almost exclusively on photosynthetic tissues; the effects of desiccation on food-conducting cells are unknown. Reported here is a cytological study of the effects of de- and rehydration on food-conducting cells in the desiccation-tolerant moss Polytrichum formosum aimed at exploring whether the remarkable subcellular organization of these cells is related to the ability of mosses to survive desiccation.• Methods Shoots of Polytrichum formosum were dehydrated under natural conditions and prepared for transmission and scanning electron microscopy using both standard and anhydrous chemical fixation protocols. Replicate samples were then fixed at intervals over a 24-h period following rehydration in either water or in a 10 µm solution of the microtubule-disrupting drug oryzalin.• Key Results Desiccation causes dramatic changes; the endoplasmic microtubules disappear; the nucleus, mitochondria and plastids become rounded and the longitudinal alignment of the organelles is lost, though cytoplasmic polarity is in part retained. Prominent stacks of endoplasmic reticulum, typical of the hydrated condition, are replaced with membranous tubules arranged at right angles to the main cellular axis. The internal cytoplasm becomes filled with small vacuoles and the plasmalemma forms labyrinthine tubular extensions outlining newly deposited ingrowths of cell wall material. Whereas plasmodesmata in meristematic cells at the shoot apex and in stem parenchyma cells appear to be unaffected by dehydration, those in leptoids become plugged with electron-opaque material. Starch deposits in parenchyma cells adjoining leptoids are depleted in desiccated plants. Rehydration sees complete reestablishment over a 12- to 24-h period of the cytology seen in the control plants. Oryzalin effectively prevents leptoid recovery.• Conclusions The results point to a key role of the microtubular cytoskeleton in the rapid re-establishment of the elaborate cytoplasmic architecture of leptoids during rehydration. The reassembly of the endoplasmic microtubule system appears to dictate the time frame for the recovery process. The failure of leptoids to recover normal cytology in the presence of oryzalin further underlines the key role of the microtubules in the control of leptoid cytological organization. [ABSTRACT FROM AUTHOR]

• Background and Aims Molecular markers have changed previous expectations about germplasm collections of endangered plants, as new perspectives aim at holding a significant representation of all the genetic diversity in the studied species to accomplish further conservation initiatives successfully. Borderea chouardii is a critically endangered allotetraploid dioecious member of Dioscoreaceae, known from a single population in the Iberian pre-Pyrenees. This population was reported to be highly structured into two genetically distinct groups of individuals corresponding to their spatial separation along the vertical cliff where it grows. In 1999, the Spanish Government of Aragón launched the first conservation programme for the ex situ preservation of this species, and since then a seed collection has been conserved at the Germplasm Bank of the Universidad Politécnica de Madrid. However, as some seed samples had not been labelled clearly at the time of collection, their origin was uncertain.• Methods Genetic variation in germplasm accessions of B. chouardii was investigated using microsatellite (simple sequence repeat; SSR) markers.• Key Results The 17 primer pairs used detected 62 SSR alleles in the 46 samples analysed from five different germplasm stocks. Eight alleles scored from the wild population were not detected in the germplasm samples analysed. The relatedness of the germplasm samples to the wild subpopulations through neighbour-joining clustering, principal coordinates analysis (PCO) and assignment tests revealed a biased higher representation of the genetic diversity of the lower cliff (43 samples) subpopulation than that of the upper cliff (three samples).• Conclusions The collection of additional samples from the upper cliff is recommended to achieve a better representation of the genetic diversity of this subpopulation. It is also recommended that these stocks should be managed separately according to their distinct microspatial origin in order to preserve the genetic substructuring of the wild population. [ABSTRACT FROM AUTHOR]

• Background and Aims The ability of partial dehydration and abscisic acid pretreatments to increase desiccation tolerance in the cyanobacterial lichen Peltigera polydactylon was tested.• Methods Net photosynthesis and respiration were measured using infrared gas analysis during a drying and rehydration cycle. At the same time, the efficiency of photosystem two was measured using chlorophyll fluorescence, and the concentrations of chlorophyll a were spectrophotometrically assayed. Heat production was also measured during a shorter drying and rehydration cycle using differential dark microcalorimetry.• Key Results Pretreating lichens by dehydrating them to a relative water content of approx. 0·65 for 3 d, followed by storing thalli hydrated for 1 d in the light, significantly improved their ability to recover net photosynthesis during rehydration after desiccation for 15 but not 30 d. Abscisic acid pretreatment could substitute for partial dehydration. The improved rates of photosynthesis during the rehydration of pretreated material were not accompanied by preservation of photosystem two activity or chlorophyll a concentrations compared with untreated lichens. Partial dehydration and ABA pretreatments appeared to have little direct effect on the desiccation tolerance of the mycobiont, because the bursts of respiration and heat production that occurred during rehydration were similar in control and pretreated lichens.• Conclusions Results indicate that the photobiont of P. polydactylon possesses inducible tolerance mechanisms that reduce desiccation-induced damage to carbon fixation, and will therefore improve the supply of carbohydrates to the whole thallus following stress. In this lichen, ABA is involved in signal transduction pathways that increase tolerance of the photobiont. [ABSTRACT FROM AUTHOR]

• Background and Aims The purpose of this study was to investigate the basis of the optimal hydration status for cryopreservation of intermediate oily seeds using Citrus as a model.• Methods The relationships between equilibrium relative humidity (RH), seed water content, presence of freezable water as determined by DSC analysis, and germination percentage after immersion in liquid nitrogen (LN) were investigated in Citrus aurantifolia, C. grandis, C. madurensis and C. reticulata. The relationship between the lipid content of seeds and their unfrozen water content was also investigated.• Key Results Independent of their level of seed desiccation tolerance, the optimal desiccation RH for seed tolerance to LN exposure was 75–80 % in the four species studied. This optimal hydration status always coincided with that at which presence of frozen water could not be detected in seed tissues during the cooling/thawing process. The unfrozen water content of seeds was variable between species and negatively correlated to seed lipid content. Using the present data, those obtained previously in seven coffee species and those reported by other authors for five other species, a significant linear relationship was found between the lipid content and the unfrozen water content of seeds.• Conclusions This study provides additional evidence that intermediate oily seeds do not withstand the presence of freezable water in their tissues during the cooling/warming process. Moreover, it offers two important applied perspectives: (1) independent of their level of desiccation tolerance, testing germination of seeds of a given oily seed species after equilibration in 75–80 % RH at 25 °C and LN exposure, gives a rapid and reliable evaluation of the possibility of cryopreserving whole seeds of this given species; (2) it is now possible to calculate the interval of water contents in which non-orthodox oily seeds of a given species are likely to withstand LN exposure as a function of their lipid content. [ABSTRACT FROM AUTHOR]

• Background and Aims Summer dormancy in perennial grasses has been studied inadequately, despite its potential to enhance plant survival and persistence in Mediterranean areas. The aim of the present work was to characterize summer dormancy and dehydration tolerance in two cultivars of Dactylis glomerata (dormant ‘Kasbah’, non-dormant ‘Oasis’) and their hybrid using physiological indicators associated with these traits.• Methods Dehydration tolerance was assessed in a glasshouse experiment, while seasonal metabolic changes which produce putative protectants for drought, such as carbohydrates and dehydrins that might be associated with summer dormancy, were analysed in the field.• Key Results The genotypes differed in their ability to survive increasing soil water deficit: lethal soil water potential (Ψs) was −3·4 MPa for ‘Kasbah’ (although non-dormant), −1·3 MPa for ‘Oasis’, and −1·6 MPa for their hybrid. In contrast, lethal water content of apices was similar for all genotypes (approx. 0·45 g H2O g d. wt−1), and hence the greater survival of ‘Kasbah’ can be ascribed to better drought avoidance rather than dehydration tolerance. In autumn-sown plants, ‘Kasbah’ had greatest dormancy, the hybrid was intermediate and ‘Oasis’ had none. The more dormant the genotype, the lower the metabolic activity during summer, and the earlier the activity declined in spring. Decreased monosaccharide content was an early indicator of dormancy induction. Accumulation of dehydrins did not correlate with stress tolerance, but dehydrin content was a function of the water status of the tissues, irrespective of the soil moisture. A protein of approx. 55 kDa occurred in leaf bases of the most dormant cultivar even in winter.• Conclusions Drought avoidance and summer dormancy are correlated but can be independently expressed. These traits are heritable, allowing selection in breeding programmes. [ABSTRACT FROM AUTHOR]

Chlorophyll‐fluorescence and infrared gas analyser measurements show saturation of photosynthetic electron flow and CO2 uptake at generally lower irradiances in Hymenophyllum tunbrigense than in H. wilsonii, but with wide variation in both species (63–189 µmol m–2 s–1 PPFD in H. tunbrigense, 129–552 µmol m–2 s–1 PPFD in H. wilsonii), probably related to both site and season. Non‐photochemical quenching (at 400 µmol m–2 s–1 PPFD) ranged from 2·1 to 8·1, with no significant difference between the species. Pressure–volume curves from thermocouple‐psychrometer measurements give full‐turgor osmotic potentials of approx. –1·4 MPa in both species, and indicate low apoplast fractions and high cell‐wall elastic moduli. Leaves of H. tunbrigense recovered within 24 h from up to 7 d desiccation at water potentials ranging from –40 MPa (74 % relative humidity, RH) to –220 MPa (20 % RH); after 15 or 30 d, desiccation recovery was slower and less complete, and leaves were severely damaged at the highest and lowest humidities. Hymenophyllum wilsonii recovered well from up to 30 d desiccation at –114 and –220 MPa, but at –40 MPa it showed signs of damage after 15 d, and was severely damaged or killed after 30 d. Results are discussed in relation to the ecological and geographical distributions of the two species, and to the adaptive strategies of filmy ferns in general. [ABSTRACT FROM AUTHOR]

The suitability of cryopreservation for the secure, long‐term storage of the rare and endangered species Cosmos atrosanguineus was investigated. Using encapsulation/dehydration of shoot tips in alginate strips, survival rates of up to 100 % and shoot regeneration of up to 35 % were achieved. Light and electron microscopy studies indicated that cellular damage to some regions of the shoot tip during the freeze/thaw procedure was high, although cell survival in and around the meristematic region allowed shoot tip regeneration. The genetic fingerprinting technique, amplified fragment length polymorphisms (AFLPs), showed that no detectable genetic variation was present between material of C. atrosanguineus at the time of initiation into tissue culture and that which had been cryopreserved, stored in liquid nitrogen for 12 months and regenerated. Weaned plantlets that were grown under glasshouse conditions exhibited no morphological variation from non‐frozen controls. [ABSTRACT FROM PUBLISHER]

Although somatic embryos of alfalfa (Medicago sativa L.) had acquired some tolerance to desiccation at the cotyledonary stage of development (22 d after plating), additional culturing in 20 μm abscisic acid (ABA) for 8 d induced greater desiccation tolerance, as determined by increased germination. Compared with fast drying, slow drying of the ABA‐treated embryos improved desiccation tolerance. However, slow drying of non‐ABA‐treated embryos led to the complete loss of germination capacity, while some fast‐dried embryos survived. An electron paramagnetic resonance spin probe technique and in vivo Fourier transform infrared microspectroscopy revealed that cellular membrane integrity and α‐helical protein secondary structure were maintained during drying in embryos cultured in media enriched with 20 μm ABA, but not in embryos cultured in the absence of ABA. Slow‐dried, non‐ABA‐treated embryos had low oligosaccharide to sucrose ratios, an increased proportion of β‐sheet protein secondary structures and broad membrane phase transitions extending over a temperature range of more than 60 °C, suggestive of irreversible phase separations. The spin probe study showed evidence of imbibitional damage, which could be alleviated by prehydration in humid air. These observations emphasize the importance of appropriate drying and prehydration protocols for the survival and storage of somatic embryos. It is suggested that ABA also plays a role in suppressing metabolism, thus increasing the level of desiccation tolerance; this is particularly evident under stressful conditions such as slow drying. [ABSTRACT FROM PUBLISHER]

This study compared the survival, electrolyte leakage and ultrastructural characteristics of embryonic axes of recalcitrant jackfruit dried rapidly (90 min) or slowly (2–3 d). Axes dried slowly showed decreased viability at higher water content than those dried rapidly; this was mirrored by an increase in electrolyte leakage at approx. 0.8 and 0.4 g H2O g−1dry mass, respectively. Rapid drying conferred relatively greater tolerance to dehydration, as attested by the 100% survival attained at approx. 0.4 g g−1in contrast to the total mortality of axes dried slowly to this water content. Partially hydrated axes were processed for microscopy using freeze-substitution to prevent rehydration artefacts. Radicles of axes dehydrated to 0.7 g g−1were examined microscopically to assess their cellular morphology and appearance of membranes following rapid or slow drying. Measurements showed that drying rate affected the distribution of water within axes, which could be relevant to the extent of stress experienced by germinative cells. Membrane breakdown was not observed in cells dehydrated either rapidly or slowly to 0.7 g g−1. Endoplasmic reticulum profiles were prominent in dehydrated cells. Autophagy was observed in axes of both treatments. The area occupied by vacuoles increased significantly only following rehydration, and was similar in axes dried rapidly or slowly. Desiccation damage became evident on rehydration, and was reversible following rapid drying but was more severe in axes dried slowly. Prolonged exposure to partial hydration may contribute to the greater sensitivity of vacuoles to damage during rehydration. Copyright 2001 Annals of Botany Company [ABSTRACT FROM AUTHOR]

Effects of dehydration, storage temperature and humidification on germination of Salix alba andS. matsudana seeds were studied. Newly released seeds showed 100% germination before and after dehydration to 11–12% moisture content. Germination of the high vigour lot (100% initial normal germination) was not affected by dehydration to 6.7% moisture content but germination decreased with further dehydration to 4.3%. The lower vigour lot (75% initial normal germination) was more susceptible to dehydration and germination decreased following dehydration to 6.7% moisture content. Dry seeds of both species survived immersion in liquid nitrogen without loss of viability. The germination of seeds stored with 9% moisture content decreased to 35–40% in 5 months at −20°C or in 2 months at 5°C. However, at 25°C seeds entirely lost viability within 2 weeks. Seeds showed improved performance when stored at −70°C > − 20°C > 5°C > 25°C and tolerated dehydration to a moisture content in equilibrium with 15% relative humidity. Results suggest that they are orthodox in storage behaviour although they are short-lived. Humidification treatment of low vigour seed lots resulted in a remarkable increase in germination percentage. Copyright 2000 Annals of Botany Company [ABSTRACT FROM AUTHOR]

This study reports the ability of Fusarium to induce orchid seed colouration and germination. The in vitro bioassay germination test, using a Fusarium isolate from the protocorm of Cypripedium reginae, was compared with standard chemical procedures of triphenyl tetrazolium chloride (TTC) and acid fuchsin (AC) for testing seed viability. With Cypripedium reginae, Cypripedium parviflorum and Platanthera grandiflora, the efficiency of the bioassay was similar to that of the TTC and AC procedures. However, the bioassay was more appropriate for estimating embryo viability after a prolonged seed pretreatment (more than 2 h) in 10% sodium hypochlorite, a surface sterilant often used to enhance germination of terrestrial species. We also obtained in vitro Cypripedium reginae seed germination induction and protocorm formation by the same Fusarium isolate. This is the first confirmation of Bernard's early reports that orchid fusaria could stimulate seed germination (Bernard N. 1990.Révue Générale de Botanique12 : 108–120). However, the importance of the non-mycorrhizal Fusarium fungus in promoting germination seems to be relatively minor compared to that of specificRhizoctonia orchid mycorrhizas. Our results are discussed in light of the current North American strategy on orchid conservation methods which proposes the use of symbiotic germination.Copyright 2000 Annals of Botany Company [ABSTRACT FROM AUTHOR]

The effects of humidification, storage in liquid nitrogen (1 or 30 d) and rewarming rate on seed germination were studied in two Spanish endemics. Humidification resulted in higher germination percentages only in the species with hard covers, especially in slowly rewarmed seeds. In an experiment lasting 21 weeks, seeds stored in liquid nitrogen were removed for 10 min each week to mimic the withdrawal of samples from a seed bank; this had no effect on germination.Copyright 1998 Annals of Botany Company [ABSTRACT FROM AUTHOR]

In vitro-grown shoot tips of five tetraploid potato (Solanum tuberosumL.) clones were cryopreserved by vitrification. Excised shoot tips (0.5–0.7 mm) were pre-cultured on filter paper discs over half strength liquid Murashige and Skoog (MS) medium supplemented with 8.7 μmGA3and different combinations of sucrose (0.3, 0.5 and 0.7m) plus mannitol (0, 0.2 and 0.4m) for 2 d under a 16 h photoperiod at 24 °C. The pre-cultured shoot tips were either successively loaded with 20 and 60% PVS 2 solutions or directly exposed to concentrated vitrification solution before physical vitrification during liquid nitrogen treatment. The vitrified shoot tips were warmed rapidly and treated with dilution mixture (MS+1.2msucrose) for 30 min before plating on regrowth medium. Addition of mannitol to the pre-culture medium improved survival of vitrified shoot tips. Direct dehydration of pre-cultured shoot tips with concentrated PVS 2 was detrimental to survival of vitrified shoot tips. Shoot tips pre-cultured on medium containing 0.3msucrose plus 0.2mmannitol, and loaded with 20% PVS 2 for 30 min followed by 15 min incubation in 60% PVS 2 and 5 min incubation in 100% PVS 2 at 0 °C resulted in up to 54% survival after vitrification. About 50% of vitrified and warmed shoot tips formed shoots directly. Post-thaw culturing of vitrified shoot tips on medium containing an elevated level of sucrose (0.2m) under diffuse light for the first week enhanced the survival rate. Continuous culturing of vitrified shoot tips on high-sucrose medium induced multiple shoot formation.Copyright 1998 Annals of Botany Company [ABSTRACT FROM AUTHOR]

It has been suggested that rate of desiccation can influence the expression of recalcitrant behaviour in seeds, thus complicating the task of determining which seeds are truly recalcitrant. The objective of this study was to see if variable rates of desiccation influenced such behaviour inQuercus nigraL., a tree seed known to be recalcitrant.Acorn moisture content, leachate conductivity, and germination were determined at various times during desiccation at three rates at 27 and 40°C. Moisture contents and germination decreased as the severity of desiccation increased. Leachate conductivity increased slightly but was not a sensitive indicator of loss of viability. The critical (lethal) moisture content for these acorns was 10–15%, although rehydration within 48 h of reaching this level prevented death in about 25% of the acorns. At 27°C any desiccation treatment that produced losses of 30–50mg of moisture per g of acorn dry weight per day should be suitable as a test for recalcitrance in the genus. Apparent physiological or fungal damage at 40°C rules out the higher temperature for such a test. [ABSTRACT FROM AUTHOR]

The accumulation of specific soluble carbohydrates has been implicated in the acquisition of desiccation tolerance and improved longevity in orthodox seeds, leading to the hypothesis that carbohydrate composition might be used as a diagnostic marker for seed storage category. We have studied the sugar composition of 46 tissues from seeds of 18 species, covering 13 genera and ten families, and representing three seed storage categories: orthodox, intermediate and recalcitrant. Soluble carbohydrate extracts from each tissue were analysed using High pH Anion Exchange Chromatography. Total sugar content and sucrose level of the embryo were highly variable across all species and no simple association with seed storage physiology was evident. Monosaccharide levels were found to be low in most seeds studied, including those of the recalcitrant category. Sucrosyl-oligosaccharides, raffinose and stachyose, were observed to be lower in recalcitrant seeds compared to orthodox seeds. In general, orthodox and recalcitrant seeds had tissues with sucrosyl-oligosaccharide:sucrose mass ratios of > 0·143 (i.e. 1:7) and < 0·083 (1:12) respectively. Moreover, large variations in the content of these sugars were noted between different tissues within the recalcitrant and intermediate seeds. The results from the present study in combination with data in the literature show that the ratio of sucrosyl-oligosaccharide isucrose in seed tissues is generally a good indicator of seed storage category. [ABSTRACT FROM AUTHOR]

The article profiles the life and works of researcher and plant physiologist Daphne J. Osborne. It notes that Osborne is a Doctor of Philosophy in the University of London in London, England supervised by R. L. Wain which marks the beginning of her research career. It mentions that her thesis titled "Studies on Plant Growth Regulators" is published in 1950 and she continues to work in this field for a lifetime. It also cites that she remains focused on research throughout her productive life.

: Background and Aims Most priming studies have been conducted on commercial seed lots of unspecified uniformity and maturity, and subsequent seed longevity has been reported to both increase and decrease. Here a seed lot of Digitalis purpurea L. with relatively uniform maturity and known history was used to analyse the effects of priming on seed longevity in air-dry storage. : Methods Seeds collected close to natural dispersal and dried at 15 % relative humidity (RH), 15 °C, were placed into experimental storage (60 % RH, 45 °C) for 14 or 28 d, primed for 48 h at 0, −1, −2, −5, −10 or −15 MPa, re-equilibrated (47 % RH, 20 °C) and then returned to storage. Further seed samples were primed for 2 or 48 h at −1 MPa and either dried at 15 % RH, 15 °C or immediately re-equilibrated for experimental storage. Finally, some seeds were given up to three cycles of experimental storage and priming (48 h at −1 MPa). : Key Results Priming at −1 MPa had a variable effect on subsequent survival during experimental storage. The shortest lived seeds in the control population showed slightly increased life spans; the longer lived seeds showed reduced life spans. In contrast, seeds first stored for 14 or 28 d before priming had substantially increased life spans. The increase tended to be greatest in the shortest lived fraction of the seed population. Both the period of rehydration and the subsequent drying conditions had significant effects on longevity. Interrupting air-dry storage with additional cycles of priming also increased longevity. : Conclusions The extent of prior deterioration and the post-priming desiccation environment affect the benefits of priming to the subsequent survival of mature seeds. Rehydration–dehydration treatments may have potential as an adjunct or alternative to the regeneration of seed accessions maintained in gene banks for plant biodiversity conservation or plant breeding. [ABSTRACT FROM AUTHOR]

: Background and Aims Models based on thermal-time approaches have been a useful tool for characterizing and predicting seed germination and dormancy release in relation to time and temperature. The aims of the present work were to evaluate the relative accuracy of different thermal-time approaches for the description of germination in Lithospermum arvense and to develop an after-ripening thermal-time model for predicting seed dormancy release. : Methods Seeds were dry-stored at constant temperatures of 5, 15 or 24 °C for up to 210 d. After different storage periods, batches of 50 seeds were incubated at eight constant temperature regimes of 5, 8, 10, 13, 15, 17, 20 or 25 °C. Experimentally obtained cumulative-germination curves were analysed using a non-linear regression procedure to obtain optimal population thermal parameters for L. arvense. Changes in these parameters were described as a function of after-ripening thermal-time and storage temperature. : Key Results The most accurate approach for simulating the thermal-germination response of L. arvense was achieved by assuming a normal distribution of both base and maximum germination temperatures. The results contradict the widely accepted assumption of a single Tb value for the entire seed population. The after-ripening process was characterized by a progressive increase in the mean maximum germination temperature and a reduction in the thermal-time requirements for germination at sub-optimal temperatures. : Conclusions The after-ripening thermal-time model developed here gave an acceptable description of the observed field emergence patterns, thus indicating its usefulness as a predictive tool to enhance weed management tactics. [ABSTRACT FROM AUTHOR]

: Background and Aims Lomatium dissectum (Apiaceae) is a perennial, herbaceous plant of wide distribution in Western North America. At the time of dispersal, L. dissectum seeds are dormant and have under-developed embryos. The aims of this work were to determine the requirements for dormancy break and germination, to characterize the type of seed dormancy, and to determine the effect of dehydration after embryo growth on seed viability and secondary dormancy. : Methods The temperature requirements for embryo growth and germination were investigated under growth chamber and field conditions. The effect of GA3 on embryo growth was also analysed to determine the specific type of seed dormancy. The effect of dehydration on seed viability and induction of secondary dormancy were tested in seeds where embryos had elongated about 4-fold their initial length. Most experiments examining the nature of seed dormancy were conducted with seeds collected at one site in two different years. To characterize the degree of variation in dormancy-breaking requirements among seed populations, the stratification requirements of seeds collected at eight different sites were compared. : Key Results Embryo growth prior to and during germination occurred at temperatures between 3 and 6 °C and was negligible at stratification temperatures of 0·5 and 9·1 °C. Seeds buried in the field and exposed to natural winter conditions showed similar trends. Interruption of the cold stratification period by 8 weeks of dehydration decreased seed viability by about 30 % and induced secondary dormancy in the remaining viable seeds. Comparison of the cold stratification requirements of different seed populations indicates that seeds collected from moist habitats have longer cold stratification requirements that those from semiarid environments. : Conclusions Seeds of L. dissectum have deep complex morphophysiological dormancy. The requirements for dormancy break and germination reflect an adaptation to trigger germination in late winter. [ABSTRACT FROM AUTHOR]

: Background and Aims Seed quality may be compromised if seeds are harvested before natural dispersal (shedding). It has been shown previously that slow or delayed drying can increase potential quality compared with immediate rapid drying. This study set out to investigate whether or not there is a critical moisture content, below which drying terminates maturation events for seeds harvested after mass maturity but before dispersal. : Methods Seeds of foxglove (Digitalis purpurea) in the post-abscission pre-dispersal phase were held at between 15 and 95 % RH for 4 or 8 d, with or without re-hydration to 95 % RH for a further 4 d, before drying to equilibrium at 15 % RH. In addition, dry seeds were primed for 48 h at −1 MPa. Subsequent seed longevity was assessed at 60 % RH and 45 °C. : Key Results Rate of germination and longevity were improved by holding seeds at a wide range of humidities after harvest. Longevity was further improved by re-hydration at 95 % RH. Priming improved the longevity of the seeds dried immediately after harvest, but not of those first held at 95 % RH for 8 d prior to drying. : Conclusions Maturation continued ex planta in these post-abscission, pre-dispersal seeds of D. purpurea dried at 15–80 % RH at a rate correlated positively with RH (cf. ageing of mature seeds). Subsequent re-hydration at 95 % RH enabled a further improvement in quality. Priming seeds initially stored air-dry for 3 months also allowed maturation events to resume. However, once individual seeds within the population had reached maximum longevity, priming had a negative impact on their subsequent survival. [ABSTRACT FROM AUTHOR]

Background and Aims Sapindaceae is one of 16 angiosperm families whose seeds have physical dormancy (PY). However, the extent and nature of PY within this family is poorly known. The primary aims of this study were: (1) to evaluate seed characteristics and determine presence (or not) of PY within nine genera of Australian Sapindaceae; and (2) to compare the frequency of PY across the phylogenetic tree within Australian Sapindaceae. Methods Viability, imbibition and seed characteristics were assessed for 14 taxa from nine genera of Sapindaceae. For five species of Dodonaea, optimal conditions for germination and dormancy break were evaluated. An in situ burial experiment was performed on D. hackettiana seeds to identify the factor(s) responsible for overcoming PY. Classes of dormancy and of non-dormancy for 26 genera of Sapindaceae were mapped onto a phylogenetic tree for the family. Key Results Mean seed viability across all taxa was 69·7 %. Embryos were fully developed and folded (seven genera) or bent (two genera); no endosperm was present. Seeds of all five Dodonaea spp. and of Distichostemon hispidulus had PY. Hot-water treatment released PY in these six species. Optimal germination temperature for seeds of the four Dodonaea spp. that germinated was 15–20 °C. Following 5 months burial in soil, 36·4 % of D. hackettiana seeds had lost PY and germinated by the beginning of the winter wet season (May). Laboratory and field data indicate that dormancy was broken by warm, moist temperatures (≥50 °C) during summer. Conclusions PY occurs infrequently in genera of Sapindaceae native to Australia. Seeds of Dodonaea and Distichostemon had PY, whereas those of the other seven genera did not. Seeds of these two genera and of Diplopeltis (a previous study) are the only three of the 20 native Australian genera of Sapindaceae for which germination has been studied that have PY; all three belong to subfamily Dodonaeoideae. [ABSTRACT FROM AUTHOR]

Background and Aims This study explores basic physiological features and time relations of recovery of photosynthetic activity and CO2 uptake following rehydration of a desiccation-tolerant moss in relation to the full temporal sequence of cytological changes associated with recovery to the normal hydrated state. It seeks reconciliation of the apparently conflicting published physiological and cytological evidence on recovery from desiccation in bryophytes. Methods Observations were made of water-stress responses and recovery using infrared gas analysis and modulated chlorophyll fluorescence, and of structural and ultrastructural changes by light and transmission electron microscopy. Key Results Net CO2 uptake fell to zero at approx. 40 % RWC, paralleling the fluorescence parameter ΦPSII at 200 µmol m–2 s–1 PPFD. On re-wetting the moss after 9–18 d desiccation, the initially negative net CO2 uptake became positive 10–30 min after re-wetting, restoring a net carbon balance after approx. 0·3–1 h. The parameter Fv/Fm reached approx. 80 % of its pre-desiccation value within approx. 10 min of re-wetting. In the presence of the protein-synthesis inhibitors chloramphenicol and cycloheximide, recovery of Fv/Fm (and CO2 exchange) proceeded normally in the dark, but declined rapidly in the light. Though initial recovery was rapid, both net CO2 uptake and Fv/Fm required approx. 24 h to recover completely to pre-desiccation values. The fixation protocols produced neither swelling of tissues nor plasmolysis. Thylakoids, grana and mitochondrial cristae remained intact throughout the drying–re-wetting cycle, but there were striking changes in the form of the organelles, especially the chloroplasts, which had prominent lobes and lamellar extensions in the normally hydrated state, but rounded off when desiccated, returning slowly to their normal state within approx. 24 h of re-wetting. Sub-cellular events during desiccation and re-wetting were generally similar to those seen in published data from the pteridophyte Selaginella lepidophylla. Conclusions Initial recovery of respiration and photosynthesis (as of protein synthesis) is very rapid, and independent of protein synthesis, suggesting physical reactivation of systems conserved intact through desiccation and rehydration, but full recovery takes approx. 24 h. This is consistent with the cytological evidence, which shows the thylakoids and cristae remaining intact through the whole course of dehydration and rehydration. Substantial and co-ordinated changes in other cell components, which must affect spatial relationships of organelles and metabolic systems, return to normal on a time span similar to full recovery of photosynthesis. Comparison of the present data with recently published results suggests a significant role for the cytoskeleton in desiccation responses. [ABSTRACT FROM AUTHOR]