ANALYSIS OF MULTIPLE CLASSES OF ABSCISIC ACID-RESPONSIVE GENES DURING EMBRYOGENESIS IN ZEA-MAYS

We have examined the effects of the plant growth regulator abscisic acid (ABA), on the accumulation of three transcripts during maize embryogenesis. The Emb5 and Rab-17 transcripts were first detected during mid embryogenesis and accumulated to high levels during late embryogenesis. In an ABA-deficient mutant, both transcripts were accumulated at very low levels. Treatment with mu M ABA during early and mid embryogenesis, but not during late embryogenesis, in the wild type and the ABA-deficient mutant enhanced the accumulation of the Emb5 and Rab-17 transcripts. The oleosin KD18 transcript was detected at moderate levels during early embryogenesis, reached a peak during mid embryogenesis and then declined gradually. Embryos incubated in the absence of ABA exhibited a rapid loss of the oleosin KD 18 transcript whereas a high level of accumulation of this transcript was maintained by incubation with nM ABA. Interestingly, the oleosin KD18 transcript was accumulated at high levels in the ABA-deficient mutant and was also detected, albeit at low levels, in an ABA-insensitive mutant. In addition, the Rab-17 transcript could be stimulated to accumulate in vegetative tissue by either ABA or water stress. Similar treatment of vegetative tissue did not induce the accumulation of Emb5 or oleosin KD18 transcripts. These results suggest that ABA-responsive genes expressed during maize embryogenesis are regulated by multiple mechanisms. (C) 1994 Wiley-Liss, Inc.