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Seed development culminates in programmed cell death (PCD) and hardening of organs enclosing the embryo (e.g., pericarp, seed coat) providing essentially a physical shield for protection during storage in the soil. We examined the proposal that dead organs enclosing embryos are unique entities that store and release upon hydration active proteins that might increase seed persistence in soil, germination and seedling establishment. Proteome analyses of dead seed coats of Brassicaceae species revealed hundreds of proteins being stored in the seed coat and released upon hydration, many are stress-associated proteins such as nucleases, proteases and chitinases. Functional analysis revealed that dead seed coats function as long-term storage for multiple active hydrolytic enzymes (e.g., nucleases) that can persist in active forms for decades. Substances released from the dead seed coat of the annual desert plant Anastatica hierochuntica displayed strong antimicrobial activity. Our data highlighted a previously unrecognized feature of dead organs enclosing embryos (e.g., seed coat) functioning not only as a physical shield for embryo protection but also as a long-term storage for active proteins and other substances that are released upon hydration to the “seedsphere” and could contribute to seed persistence in the soil, germination and seedling establishment. [ABSTRACT FROM AUTHOR]

Background: Seed of Shismus arabicus, a desert annual, display a seasonal tolerance to dehydration. The occurrence of a metabolic seasonal rhythm and its relation with the fluctuations in seed dehydration tolerance was investigated. Results: Dry seeds metabolism was the least affected by the season, while the metabolism of germinated and dehydrated seeds exhibit distinct seasonal patterns. Negative associations exist between amino acids, sugars and TCA cycle intermediates and seed survival, while positive relations exist with seed germination. In contrast, associations between the level of secondary metabolites identified in the dehydrated seeds and survival percentage were evenly distributed in positive and negative values, suggesting a functional role of these metabolites in the establishment of seed dehydration tolerance. Conclusion: Our results indicate the occurrence of metabolic biorhythms in germinating and dehydrating seeds associated with seasonal changes in germination and, more pronouncedly, in seed dehydration tolerance. Increased biosynthesis of protective compounds (polyphenols) in dehydrating seeds during the winter season at the expenses of central metabolites likely contributes to the respective enhanced dehydration tolerance monitored. [ABSTRACT FROM AUTHOR]

This study examined dispersal units, caryopsis size groups, the inhibitory effect of loess soil on germination and the rate of germination of Schismus arabicus caryopses. Germination of small batches of the seeds from the large, long-lasting soil seed bank of S. arabicus contributes to its success as a very common annual plant in large areas of the Negev, under the unpredictable small amounts and distribution of rain. The lower the percentage of germinating caryopses on local loess soil, and the faster the speed of germination (from 4 h) of caryopses that do germinate, the higher is the chance of plants survival to reproduce. [Copyright &y& Elsevier]

AbstractSeveral environmental factors have pronounced influences on the complementary sets of survival strategies, at different stages of the plant life cycle, of some of the most common annual plants in the Negev Desert, Israel. Plasticity of seed germination may spread germination over time and thus reduce the risk to species survival. This plasticity may be affected by day length during seed development and maturation and by position of seeds on mother plants. Post-seed maturation dry storage temperatures may affect the duration of after-ripening. The tiny, dust-like seeds produced by some plants that are dispersed by wind after maturation may escape massive seed predation and remain in large seed banks in the soil. Seeds of other species are protected in lignified structures in aerial seed banks on dead, dry, lignified mother plants. Seed dispersal strategies from these aerial seed banks by rain may also prevent massive seed collection by animals. The ‘cautious’ or ‘opportunistic’ germination strategy and seedling drought tolerance may increase seedling survival in many of the plant species under the unpredictable amounts and distribution of rain in these desert areas. Factors such as amount of rain, temperature, relative humidity, time of the beginning of soil wetting (day or night), seed size and history and the depth of seeds in the soil may affect germination percentages. Day length and soil water content during plant development may have a pronounced influence on plant age at first flowering, seed yield and plant life span. [ABSTRACT FROM AUTHOR]