RESPONSE OF BRASSICA-NAPUS L MICROSPORE-DERIVED EMBRYOS TO EXOGENOUS ABSCISIC-ACID AND DESICCATION

Microspore-derived embryos from Brassica napus cv. Topas (low erucic acid) and Reston (high erucic acid) were subjected to treatment with abscisic acid (ABA) during late-stage embryo development and then dried under controlled relative humidities to mature dry seed levels of moisture. Exogenously medium-supplied ABA arrested growth and development, reduced moisture content, increased total fatty acids on a dry weight basis, and stimulated synthesis of proteins in microspore-derived embryos. ABA also resulted in a higher proportion of 22:1 in cv. Reston (high 22:1) and increased the level of fatty acid unsaturation in cv. Topas (low 22:1). The accumulation of two proteins that co-migrated with cruciferin and napin on sodium dodecyl sulfate-polyacrylamide gel electrophoresis and two-dimensional gels were also promoted by exposure to ABA, and the degree of accumulation was dependent on the concentration and time of application of ABA. Controlled desiccation of microspore embryos, used to simulate normal maturation and dehydration of zygotic embryos during seed development, did not seem to cause an increase of either storage proteins, total fatty acids, or 22:1 (in cv. Reston), suggesting that dehydration is not a prerequisite for these processes, at least in cultured Brassica embryos.