INDUCTION OF LIPID AND OLEOSIN BIOSYNTHESIS BY (-ABSCISIC ACID AND ITS METABOLITES IN MICROSPORE-DERIVED EMBRYOS OF BRASSICA-NAPUS L CV RESTON - BIOLOGICAL RESPONSES IN THE PRESENCE OF 8'-HYDROXYABSCISIC ACID())

Microspore-derived (MD) embryos of Brassica napus L. cv Reston were us ed to test the effects of (+)-abscisic acid ([(+)-ABA]) and its metabo lites, 8'-hydroxyabscisic acid (8'-OH ABA) and (-)-phaseic acid (PA), on the accumulation of very long-chain monounsaturated fatty acids (VL CMFAs) and induction of genes encoding a 19-kD oleosin protein and a D elta 15 desaturase during embryogenesis. Developing early- to mid-coty ledonary MD embryos at 16 to 19 d in culture were treated with 10 mu M hormone/metabolite for 4 d. At various times during incubation, embry os and medium were analyzed to determine levels of hormone/metabolite, VLCMFAs, and oleosin or Delta 15 desaturase transcripts. The VLCMFAs, 20:1 and 22:1, primarily in triacylglycerols, increased by 200% after 72 h in the presence of (+)-ABA and 8'-OH ABA relative to the control . In contrast, treatment with PA for 72 h had little effect (20% incre ase) on the level of VLCMFAs. The first 24 to 72 h of (+)-ABA treatmen t were critical in the induction of VLCMFA biosynthesis, with 8'-OH AB A lagging slightly behind (+)-ABA in promoting this response. The accu mulation of VLCMFAs was positively correlated with an increase in elon gase activity. (+)-ABA and its 8'-OH ABA metabolite induced the accumu lation of a 19-kD oleosin transcript within 2 to 4 h in culture. In ad dition, both (+)-ABA and 8'-OH ABA induced the same level of Delta 15 desaturase transcript by 8 h. PA had no effect on the induction of eit her oleosin or Delta 15 desaturase transcripts. To our knowledge, this is the first report of the biological activity of 8'-OH ABA and of st imulatory effects of (+)-ABA and 8'-OH ABA on lipid and oleosin biosyn thesis.