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ABSTRACT: Many species within the genus Cuphea (Lythraceae) produce seed with high levels of medium-chain fatty acids. Seeds of some Cuphea species lose viability when placed into storage at -18 degrees C. These species tolerate significant drying to 0.05 g/g and may, therefore, be intermediate in their storage characteristics. The thermal properties of seed lipids were observed using differential scanning calorimetry. Species with peak lipid melting temperatures >/=27 degrees C were found to be sensitive to -18 degrees C exposure while those with melting temperatures <27 degrees C were able to tolerate low-temperature exposure. This relationship was determined by the triacylglycerol composition of the individual species. Sensitive species have high concentrations of lauric acid (C(12)) and/or myristic acid (C(14)). Species with high concentrations of capric (C(8)) or caprylic acid (C(10)) or with high concentrations of unsaturated fatty acids tolerate low temperature exposure. Potential damage caused by low temperature exposure can be avoided by exposing seeds to a brief heat pulse of 45 degrees C to melt solidified lipids prior to imbibition. The relationship between the behavior of triacylglycerols in vivo, seed storage behavior and sensitivity to imbibitional damage is previously unreported and may apply to other species with physiologies that make them difficult to store.
Planta 09/2003; 217(5):699-708. · 3.00 Impact Factor
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ABSTRACT: Seeds of the endangered species Zizania texana are recalcitrant, making it difficult to preserve the remaining genetic diversity of this species in genebanks. Excised embryos can be cryopreserved using solution-based cryoprotection protocols. Survival following cryoexposure increased from less than 5% to about 75% by preculturing embryos in high concentrations of sugars, bathing them in cryoprotectant solutions, and partially drying them to water contents of about 0.6 g H2O/g dry mass.
Cryo letters 05/2002; 23(5):291-8. · 1.25 Impact Factor
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ABSTRACT: Embryonic axes of tea (desiccation sensitive) and pea (desiccation tolerant) were dried at different rates or stored at different water contents to distinguish between damage associated with the immediate effects of water loss and the longer-term effects of a partially hydrated state. No loss of viability was observed if pea axes were dried sufficiently rapidly (from 1.8 to 0.1 g H2O g-1dry mass (g/g) within 5 d). However, viability was lost in tea axes dried below 0.5 g/g (approximately -15 MPa) even if axes were dried within 1 h. Death in tea axes dried to moisture contents less than 0.5 g/g probably resulted from the removal of water necessary for cellular structural integrity (i.e. desiccation damage sensu stricto). When axes of both species were dried at slower rates, viability losses were observed at water potentials between about -3 and -15 MPa. The timing for this type of damage was species dependent, occurring within 2 d for tea and after 5 d for pea, and may be explained by higher oxidative activity in tea compared to pea. Embryos of both species with water potentials below -3 MPa were lethally damaged if oxygen consumption exceeded 1000–5000 μmol O2 g-1dry mass. Recalcitrant seeds are different than orthodox seeds because the former do not survive drying below a critical water content, regardless of the drying rate. Rapid drying is required for accurate assessment of the critical water content. Slow drying leads to metabolic imbalance and artefactual assessment of the critical water content for desiccation damage. Both tea and pea seeds were susceptible to damage from metabolic imbalances, suggesting that the predominant stress from slow drying is ageing.
Seed Science Research 05/2001; 11(02):135 - 148. · 1.06 Impact Factor
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ABSTRACT: Seed genebanks around the world are seeking economical ways to store seeds as a means of conserving plant biodiversity. Zheng
Nature 10/1998; 395(6704):758-758. · 36.28 Impact Factor
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ABSTRACT: Germplasm must be stored under optimal conditions to maximize longevity and efficiently maintain genetic resources. In order to identify optimal storage conditions, we investigated the effects of temperature (−5 to 45°C) and water content (<0.17 g H2O g−1 dry weight) on longevity of Typha latifolia L. pollen. Longevity was highest at water contents corresponding to storage relative humidity (RH) of 11-15% which corresponded to the shoulder of water sorption isotherms. Also coinciding with this shoulder were abrupt changes in heat capacity of water present in the pollen. Consistent with changes in isotherms with temperature and the concept of critical RH for storage, optimum water contents increased with decreasing temperature. An attempt was made to explain the aging behavior according to the glass concept. The water content-temperature combinations of optimal storage were found to be below the glass transition curve, indicating that optimum storage conditions are achieved when intracellular glasses are present. We also found a change in activation energy of aging in Arrhenius plots around Tg, demonstrating a change in aging kinetics when the glassy state is lost. We concluL that Tg curves cannot be used solely to predict precise conditions of optimum storage, but might be useful for predictions of storage longevity above optimum water contents. The data imply that too much drying reduces longevity and should be avoided, particularly when cryogenic storage is considered.
Physiologia Plantarum 05/1998; 103(2):145 - 153. · 3.11 Impact Factor
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ABSTRACT: The present study investigated the relative contributions of water content and non-equilibrium cooling and warming rates to the survival of cryopreserved axes of recalcitrant P. trifoliata seeds. Reducing water contents from 1.7 and 0.26 g water per g dry mass is believed to increase cytoplasmic viscosity. Cooling to -196 degree C was done at rates averaging between 0.17 and 1300 degree C per second, and warming at 600 or 1.35 degree C per second. Survival was assessed after 4 weeks in vitro. Rapid warming resulted in higher survival and normal development of axes at all water contents. The effects of cooling rate were dependent on the water content of axes. Cooling rates resulting in >70 percent normal development ranged between 0.17 and about 1300 degree C per second for axes at a water content of 0.26 g water per g dry mass narrowing with increasing hydration to an apparent optimum at about 686 degree C per second in axes at 0.8 g water per g dry mass At 1.7 g water per g dry mass, axes cooled at 0.17 degree C per second yielded nearly 40 percent normal development, whereas faster cooling was deleterious. Results are interpreted in the context of the effect of water content on cytoplasmic viscosity and the rate of intracellular ice formation. At low water contents, the high intracellular viscosity slows ice crystallization making survival independent of cooling rate. At higher water contents, the reduced viscosity requires faster cooling to prevent ice crystal damage. The ability to cool rapidly with increasing hydration is balanced with an increasing limitation to dissipate heat fast enough to prevent severe damage.
Cryo letters 25(2):129-38. · 1.25 Impact Factor
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ABSTRACT: Cryopreservation using a winter vegetative bud method is being applied to the Malus collection maintained in the field at the USDA-ARS Plant Genetic Resources Unit, Geneva, New York. Winter hardy materials are sent to the USDA-ARS National Center for Genetic Resources Preservation, Fort Collins, CO, for processing. To date 1915 accessions, representing 30 species and 16 interspecific hybrids, have been tested. The NCGRP minimum standard for cryopreservation is 40% viable buds, as determined by grafting. For M. x domestica 95% of the accessions tested have been cryopreserved. For species other than M. x domestica, 83% have met the criterion. Eight lines were collected, cryopreserved and recovered through grafting each year. Data from this set showed an affect of year and cultivar on success. There was no strong relationship between viability after cryopreservation and phylogeny. For North American species success after cryopreservation was related to geographical origin.
Cryo letters 25(5):323-34. · 1.25 Impact Factor
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ABSTRACT: Seeds die inevitably but unexpectedly during storage and current understanding of seed quality and storage conditions do not allow reliable means to predict or prevent this critical problem. Chemical degradation of seed components likely occurs through oxidative damage, but the rate of these reactions is dominated by properties of seed that are affected by temperature and moisture. These visco-elastic properties contribute to the structure of seeds as amorphous solids. This paper presents the perspective of seed maturation and post-harvest treatment as an exercise in engineering design for a structure that must persist through time and fluctuating conditions. Structural analyses are engineering tools used to select proper composition of materials and predict their behavior under a range of circumstances and are applicable to measurement within seeds. Thermal mechanical analysis (TMA) and dynamic mechanical analysis (DMA) measure structural deformation and stress–strain relationships, providing sensitive and universal parameters that detect differences in structural stability in materials with subtle compositional differences or processing methods. When applied to seeds, TMA and DMA techniques provide information consistent with existing information on glass and first order transitions. The depth of additional information obtainable about the behavior of the glass and interactions with lipid structure suggests that these techniques will be able to quantify differences among seed structures that contribute to their tendency to age.
Plant Science.
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ABSTRACT: Seed shelf-life or longevity is difficult to predict or to measure on a practical time scale. Predictive models suggest that water has the same effect on ageing rate for all seed lots within a species and that initial seed quality is the dominating factor explaining within-species variation. These assumptions are used in ‘accelerated ageing’ or ‘controlled deterioration’ (AA/CD) tests, which are commonly used to predict seed longevity in commercial and research applications. In this study, we describe within-species variation of longevity for seeds of Secale cereale and S. strictum (cultivated rye and its wild progenitor) under typical dry storage conditions of a genebank, and show that initial seed quality is an important, but not sole, factor explaining measured longevity. We also test the correlation of seed longevity, measured under humid and dry conditions, using 50 cultivars of rye, wheat (Triticum aestivum) and the intergeneric cross triticale, to assess how well AA/CD tests predict seed shelf-life during dry storage. Known differences in longevity between wheat and rye were confirmed at all water contents, and triticale seeds demonstrated intermediate behaviour. Longevity measured for humid and dry conditions were weakly correlated when comparisons included all grain types and were not correlated in within-grain-type comparisons. Response to moisture varied among cultivars. These findings do not support assumptions made in seed ageing models that use AA/CD tests. Our results suggest that more traits are involved in the expression of seed longevity than those typically measured in studies of initial seed vigour.
