Differential responses to different light spectral ranges of violaxanthin de-epoxidation and accumulation of Cbr, an algal homologue of plant early light inducible proteins, in two strains of Dunaliella

Unicellular green algae of the genus Dunaliella, similar to higher plants, respond to light stress by enhanced de-epoxidation of violaxanthin and accu mulation of Cbr, a protein homologous to early light inducible proteins (El ips) in plants. These proteins belong to the superfamily of chlorophyll a/b binding proteins. Two Dunaliella strains, D. bardawil and D. salina, were compared for these two responses under light in the UVA, blue, green and re d spectral ranges. In D. bardawil, the two stress responses were similarly induced under UVA, blue or red light and to a lesser extent under green lig ht. In D. salina, a similar spectral range dependence was exhibited for vio laxanthin de-epoxidation. However, Cbr accumulated only under UVA or blue l ight but not under green or red light. A strong synergistic effect of a low dose of blue light superimposed on red light resulted in Cbr accumulation. These results reveal strain-specific differences in spectral range require ments of the two light-stress responses. In the two strains, violaxanthin d e-epoxidation is triggered under photosynthetically-active spectral ranges but at least in D. salina, Cbr accumulation appears to require a specific l ight signal additionally to a signal(s) generated by light stress. (C) Edit ions scientifiques et medicales Elsevier SAS.