Mechanism of desiccation tolerance of somatic embryos and application of dry artificial seeds

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Desiccation tolerance of microspore-derived embryos of Brassica spp.are induced by exogenous application of ABA.The objective of this study was to investigate the mechanism by which ABA induces desiccation tolerance and to clear some traits of the desiccated embryos for utilizing as dry artificial seeds.1.Late embryogenesis abundant (Lea) genes are considered to be related to the desiccation tolerance of zygotic embryos. Accumulation of Lea mRNA was detected in desiccation tolerant embryos, but not in desiccation sensitive ones. Both induction of desiccation tolerance of embryos and Lea mRNA accumulation were simultaneously occurred within 12h of ABA treatment. Lea genes were isolated form cDNA libraries derived from desiccation-tolerant microspore embryos of rapeseed and Chinese cabbage. Nucleotide sequence was determined on ME-leaN4 clone of rapeseed and ME-leaC4 of Chinese cabbage. Predicted amino acid sequence of these clones showed that 82% homology was present between two polypeptides, and that two 11 residue repeats with consensus sequences were present 11 and 9 times in rapeseed and Chinese cabbage, respectively. Isolation of Lea gene from genomic library of rapeseed indicated that ABA responsive elements (ABRE) were present in the promoter of Lea gene.2.To elucidate the function of Lea gene, Lea gene which was regulated by CaMV35S promoter was introduced into tobacco and rapeseed. Though 6 tobacco transgenic and 2 transgenic rapeseed plants were obtained, they did not show increased tolerance to salinity. However, a few tobacco plants showed slightly higher growth rates than nontransgenic plants in seedling of T1 generation.3.The desiccated embryos stored at-80ﾟC maintained their ability of plant regeneration for 3 years, and had the ability of cryopreservation. Viability of desiccated embryos was easily able to be determined by seed exudate method.