Light regulation of gibberellin A(1) content and expression of genes coding for GA 20-oxidase and GA 3 beta-hydroxylase in etiolated pea seedlings

White light (WL) inhibited the stem elongation of etiolated pea (Pisum sati vum L.) seedlings and the inhibition was partially reversed by the applicat ion of gibberellin A(1) (GA(1)), the active GA in shoot growth, The amount of GA(1) in the apical shoot was reduced to about 25% after 2 h of WL, and to a trace level after 4 h, The effect of light on GA(1) content was revers ed when the plants were transferred again to the dark after 6 h of WL. The effect of light on the expression of GA 20-oxidase and GA 3 beta-hydroxylas e genes, coding for the last steps of GA(1) biosynthesis, was also investig ated. Contrary to expectations, the amounts of GA 20-oxidase and GA 3 beta- hydroxylase transcripts increased in the entire apical shoot of WL-irradiat ed seedlings, and this increase was negated in seedlings treated with GA(1) before WL irradiation, probably as a result of negative feed-back regulati on. The effect of WL on GA 20-oxidase transcripts was mainly localized in t he apex (hook) whereas the effect on GA 3 beta-hydroxylase transcripts was mainly localized in the subapical tissues, Red and far-red light also enhan ced the GA 20-oxidase transcript level, but not that of GA 3 beta-hydroxyla se, suggesting that different photoreceptors are involved in the regulation of these genes by WL, The results presented indicate that the inhibition o f stem elongation by light is due, at least partially, to a decrease of GA( 1) content by a still unknown mechanism. The increase of GA(8) upon WL irra diation raises the possibility that an inactivation activity may be involve d in the control of the content of GA(1) by light.