Regulation of gibberellin 20-oxidase and gibberellin 3 beta-hydroxylase transcript accumulation during de-etiolation of pea seedlings

Gibberellin (GA) 20-oxidase (GA 20-ox) and GA 3 beta-hydroxylase (GA 3 beta -hy) are enzymes that catalyze the late steps in the formation of active GA s, and are potential control points in the regulation of GA biosynthesis by light. We have investigated the photoregulation of the GA 20-ox and GA 3 b eta-hy transcript levels in pea (Pisum sativum L.). The GA 20-ox transcript level was higher in light-grown seedlings than in etiolated seedlings, whe reas GA 3 beta-hy mRNA accumulation was higher in etiolated seedlings. Howe ver, transfer of etiolated seedlings to light led to a 5-fold increase in t he expression of both transcripts 4 h after transfer. GA 20-ox mRNA accumul ation is regulated by both phytochromes A and B. Transfer to light also res ulted in a 6-fold decrease in GA(1) levels within 2 h. These results sugges t that the light-induced drop in GA(1) level is not achieved through regula tion of GA 20-ox and GA 3 beta-hy mRNA accumulation. The application of exo genous GA(1) to apical buds of etiolated seedlings prior to light treatment s inhibited the light-induced accumulation of both GA 20-ox and GA 3 beta-h y mRNA, suggesting that negative feedback regulation is an important mechan ism in the regulation of GA 20-ox and GA 3 beta-hy mRNA accumulation during de-etiolation of pea seedlings.