BIOLOGICAL-ACTIVITY OF OPTICALLY PURE C-1 ALTERED ABSCISIC-ACID ANALOGS IN BRASSICA-NAPUS MICROSPORE EMBRYOS

We have examined the effects of stereochemically pure analogs of absci sic acid (ABA) on three responses in Brassica napus microspore embryos , The analogs used include modifications to natural (S-) (+)-ABA (=N-A BA) at the C-1 and C-1' positions. At the C-l position, the carboxylic acid function was replaced with an alcohol, aldehyde, or methyl eater functional group, and at the chiral C-1' position both enantiomers we re prepared. The rationale for choosing these particular analogs was t hat they had previously shown some potential as slow release forms of ABA (Gusta LV, Ewan B, Reaney MJT, Abrams SR (1992) Can J Bet. 70:1550 -1555). The responsiveness of microspore-derived embryos of B. napus t o these analogs was investigated. Three types of responses were evalua ted: (1) the inhibition of precocious germination; (2) induction of ol eosin gene expression; and (3) induction of napin gene expression. All of the structural analogs of ABA tested were effective in the three a ssays, regardless of functional group substitution or stereochemistry. However, the three assays showed differential sensitivity to the vari ous analogs. The U-forms of abscisyl alcohol and abscisyl aldehyde wer e very effective in inhibiting precocious germination (greater than na tural ABA). Oleosin mRNA accumulation responded most effectively to U- abscisyl alcohol, while the N-abscisyl aldehyde and ABA methyl eater w ere the most effective at inducing napin mRNA accumulation, This work highlights the distinct differences in activity which result from usin g stereochemically pure analogs. In addition, surprisingly potent resp onses are reported in one or more of the assays for abscisyl aldehyde and abscisyl alcohol.