PLANT PHYSIOLOGY , Vol 110, Issue 4 1405-1411, Copyright © 1996 by American Society of Plant Biologists
Possible Role of Cbr, an Algal Early-Light-Induced Protein, in Nonphotochemical Quenching of Chlorophyll Fluorescence
P. Braun, G. Banet, T. Tal, S. Malkin and A. Zamir
Biochemistry Department, Weizmann Institute of Science, Rehovot 76100, Israel
The unicellular green alga Dunaliella bardawil exhibits typical responses
to excessive light when starved for sulfate under normal light (60 [mu]E
m-2 s-1) but not under low light (14 [mu]E m-2 s-1). Algae were analyzed
during several days of sulfate starvation for nonphotochemical quenching of
chlorophyll fluorescence in the absence or presence of the uncouplers
SF-6847 (SF) or carbonyl cyanide p- trifluoromethoxyphenyl hydrazone.
Parallel analyses followed two light-stress responses: (a) violaxanthin
conversion to zeaxanthin and (b) accumulation of Cbr, a protein analogous
to plant early-light-induced proteins and implicated in zeaxanthin binding.
In cells starved under normal light SF inhibited nonphotochemical quenching
during the first 24 h, but not from 40 h onward. In cells starved under low
light SF inhibited nonphotochemical quenching throughout the starvation
period. Under normal light accumulation of zeaxanthin was nearly maximal by
24 h, but Cbr was fully induced only by 40h. Under low light zeaxanthin
accumulated slowly but no Cbr was evident. These results suggest that
during exposure to excessive light, the initial pH gradient-dependent,
Cbr-independent mode of nonphotochemical quenching is modified to become
less dependent on pH gradient and requires Cbr.
