J. Gil et Jl. Garcia-martinez, 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, PHYSL PLANT, 108(2), 2000, pp. 223-229
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.