Dormancy in rice (Oryza sativa L.) seed is imposed by certain physical and chemical factors associated with its covering structures, i.e.hull and pericarp. The nature of these germination blocks, their mode ofaction, and processes regulating the release of dormancy are not fully understood. Of nine rice cultivars studied, Ching-shi 15, Stejaree 45, PTB10, and Mahsuri are weakly dormant, and Bansphul, Benaful, Kataktara, Dular, and N22 are dormant. Release of seed dormancy in rice by various treatments, oxidative processes and enzymic changes associated with dormancy, and parallelism between natural and artificially imposed dormancy patterns were examined. The influence of the hull in imposing dormancy was stronger and more prolonged than that of the pericarp. Application of GA3 was effective in inducing germination only in weakly dormant cultivars. Dormancy was completely released in all cultivars by subjecting the seeds to moist heat treatment, by removing the hull and pericarp, and by applying GA3 after dehulling. Dormant cultivars had higher O2 uptake rate and peroxidase activity and lower amylase and dehydrogenase activities than the weakly dormant ones. Hull removal substantially decreased peroxidase activity but enhanced amylase and dehydrogenase activities. Nonanoic acid (C90), a short-chain saturated fatty acid (SCSFA), when exogenously applied to non-dormant seeds imposed dormancy. Dry heat treatment or presoaking in 0.01 m KNO3 or 0.1 m H2O2 was very effective in releasing SCSFA-imposed dormancy. Amylase activity was greatly reduced by treatments with nonanoic acid (C90) or ABA. Considering earlier reports and results of the present study, it is proposed that seed dormancy in rice is regulated both by the presence of SCSFAs and ABA in the hull and the pericarp. The relative significance of these substances in cultivars of tropical and temperate origins and its implications in terms of ecogeographic adaptability are discussed.

Storage of seeds for extended periods causes a number of degradative changes related to the aging process such as decreased seedling vigor and reduced germination. In this study, molecular markers were used to study the aging process in seeds of two different plants species. Seeds of three differentially aged seed groups, including control (un-aged), naturally aged, and accelerated aging, from soybean (Glycine max) and safflower (Carthamus tinctorius) were evaluated for genetic variability using random amplification of polymorphic DNA (RAPD), amplified fragment length polymorphism (AFLP), and simple sequence repeat (SSR) markers. For both plant species, naturally aged and accelerated aged groups clustered together with RAPD markers, whereas control and naturally aged seeds showed similarity in both AFLP and SSR profiles. Based on these findings, it can be concluded that observed changes in DNA profiles of seeds from different aged groups did not contribute to accumulation of genetic variations of the same magnitude. Therefore, seed of similar viability must be selected for molecular marker analysis for plant variety protection, among other comparative studies.

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Thirty-three soybean [Glycine max (L.) Merill] genotypes, comprising 14 black-seeded and 19 yellow-seeded ones, were selected on the basis of their reported storability for the biochemical phenotyping to establish the role of lipid peroxidation and antioxidant enzymes in seed longevity. The present study revealed clear genotypic variability with respect to storability among different soybean genotypes. Good-storer genotypes with lower electrolyte leakage were characterized by smaller seed size with black testa color. The level of volatile aldehydes released and lipoxygenase II enzyme activity were higher in the yellow-seeded genotypes than in the black-seeded genotypes, though it increased in all during ageing. A sharp increase in the release of volatile aldehydes and lipoxygenase II activity, concomitant with the reduction in germination under uncontrolled laboratory conditions of storage indicated the role of lipid peroxidation in seed longevity behavior (r = -0.6638** and r = -0.7639**, respectively). No significant difference was noted in the mean hydroperoxide lyase activity of black and yellow-seeded genotypes. However, maintenance of high hydroperoxide lyase activity during storage resulted in higher release of volatile aldehydes and poor storability of seeds. Significantly higher antioxidant enzyme activity was recorded in the black-seeded genotypes than in the yellow-seeded ones, though there was a reduction in hydroperoxide lyase activity during storage in all the genotypes. The viability of black-seeded genotypes after storage for 1 year was better than the yellow-seeded genotypes.

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