TEMPORAL, SPATIAL AND HORMONAL-REGULATION OF THE S-ADENOSYLMETHIONINESYNTHETASE GENE IN PETUNIA

Gibberellic acid (GA(3)) promotes corolla elongation and pigmentation in petunia flowers. We have previously shown that GA(3) induces pigmen tation by activating specific genes of the anthocyanin biosynthetic pa thway. The aim of the present work was to examine whether GA(3) induce s also the expression of genes from other metabolic pathways in petuni a corollas that may be associated with growth. Recently we reported Th e cloning of the petunia sam gene coding for S-adenosylmethionine synt hetase (SAMS). In the present work we show that sam expression is indu ced by GA(3) in both corollas and stems. The expression of the gene wa s correlated with corolla elongation. GA, and the cytokinin, N-6-benzy ladenine (BA) promoted corolla growth and sam expression, whereas absc isic acid (ABA) inhibited corolla elongation and repressed sam mRNA ac cumulation. An analysis of sam expression in stems indicated a high le vel in young, elongating internodes and a very low level in the mature , non-elongating stem zone. The results of the present study show that the effect of GA(3) on gene expression in the corolla of petunia, is not restricted to the anthocyanin biosynthetic pathway;they also sugge st a possible role for sam in GA(3)-induced corolla and stem elongatio n.