ALTERED XANTHOPHYLL COMPOSITIONS ADVERSELY AFFECT CHLOROPHYLL ACCUMULATION AND NONPHOTOCHEMICAL QUENCHING IN ARABIDOPSIS MUTANTS

Collectively, the xanthophyll class of carotenoids perform a variety o f critical roles in light harvesting antenna assembly and function. Th e xanthophyll composition of higher plant photosystems (lutein, violax anthin, and neoxanthin) is remarkably conserved, suggesting important functional roles for each, We have taken a molecular genetic approach in Arabidopsis toward defining the respective roles of individual xant hophylls in vivo by using a series of mutant lines that selectively el iminate and substitute a range of xanthophylls. The mutations, lut1 an d lut2 (lut = lutein deficient), disrupt lutein biosynthesis. In lut2, lutein is replaced mainly by a stoichiometric increase in violaxanthi n and antheraxanthin, A third mutant, aba1, accumulates normal levels of lutein and substitutes zeaxanthin for violaxanthin and neoxanthin, The lut2aba1 double mutant completely lacks lutein, violaxanthin, and neoxanthin and instead accumulates zeaxanthin, All mutants were viable in soil and had chlorophyll alb ratios ranging from 2.9 to 3.5 and ne ar wild-type rates of photosynthesis. However, mutants accumulating ze axanthin exhibited a delayed greening virescent phenotype, which was m ost severe and often lethal when zeaxanthin was the only xanthophyll p resent. Chlorophyll fluorescence quenching kinetics indicated that bot h zeaxanthin and lutein contribute to nonphotochemical quenching; spec ifically, lutein contributes, directly or indirectly, to the rapid ris e of nonphotochemical quenching, The results suggest that the normal c omplement of xanthophylls, while not essential, is required for optima l assembly and function of the light harvesting antenna in higher plan ts.