Involvement of plasma membrane redox activity and calcium homeostasis in the UV-B and UV-A blue light induction of gene expression in Arabidopsis

UV and blue light are important regulators of plant gene expression and dev elopment. We investigated the signal transduction processes involved in the induction of chalcone synthase (CHS) and phenylalanine ammonia-lyase (PAL) gene expression by UV-B and UV-A/blue right in an Arabidopsis cell suspens ion culture. Experiments with electron transport inhibitors indicated that plasma membrane redox activity is involved in both signal transduction path ways. Calcium ionophore treatment stimulated expression of the TOUCH3 gene, and this induction was strongly antagonized by UV-A/blue and UV-B tight, s uggesting that both light qualities may promote calcium efflux from the cyt osol. Consistent with this hypothesis, experiments with specific inhibitors indicated that UV-B and UV-A/blue light regulate calcium levels in a cytos olic pool in part via the action of specific Ca2+-ATPases. On the basis of these and previous findings, we propose that plasma membrane redox activity , initiated by photoreception, is coupled to the regulation of calcium rele ase from an intracellular store, generating a calcium signal that is requir ed to induce CHS expression.