ANION CHANNELS AND THE STIMULATION OF ANTHOCYANIN ACCUMULATION BY BLUE-LIGHT IN ARABIDOPSIS SEEDLINGS

Activation of anion channels by blue light begins within seconds of ir radiation in seedlings and is related to the ensuing growth inhibition . 5-Nitro-2-(3-phenylpropylamino)-benzoic acid (NPPB) is a potent, sel ective, and reversible blocker of these anion channels in Arabidopsis thaliana. Here we show that 20 mu M NPPB blocked 72% of the blue-light -induced accumulation of anthocyanin pigments in seedlings. Feeding bi osynthetic intermediates to wild-type and tt5 seedlings provided evide nce that NPPB prevented blue light from up-regulating one or more step s between and including phenylalanine ammonia lyase and chalcone isome rase. NPPB was found to have no significant effect on the blue-light-i nduced increase in transcript levels of PAL1, CHS, CHI, or DFR, which are genes that encode anthocyanin-biosynthetic enzymes. Immunoblots re vealed that NPPB also did not inhibit the accumulation of the chalcone synthase, chalcone isomerase, or flavanone-3-hydroxylase proteins. Th is is in contrast to the reduced anthocyanin accumulation displayed by a mutant lacking the HY4 blue-light receptor, as hy4 displayed reduce d expression of the above enzymes. Taken together, the data indicate t hat blue light acting through HY4 leads to an increase in the amount o f biosynthetic enzymes, but blue light must also act through a separat e, anion-channel-dependent system to create a fully functional biosynt hetic pathway.