Characterization of the thylakoid membranes of the tobacco aurea mutant Su/su and of three green revertant plants.

Phenotypic characterizations of the semidominant aurea tobacco (Nicotiana tabacum L.) mutant Su/su, the homozygous mutant Su/Su and three green revertants (R1, R2, and R3) are presented. The leaf color of Su/su plants varies from yellow to light-green when grown under high and low energy fluence rates (33.0 and 3.3 W m(-2)), respectively. The change in visual phenotype under high-light conditions is correlated with decreased content of chlorophyll per leaf area, agranal chloroplast ultrastructure, changes in the number of chlorophyll-protein complexes, and absence of two or more of the light harvesting chlorophyll-polypeptides of 25,000-29,000 dalton. The homozygous mutant grown under low light was shown to be completely lacking in grana stacks and to be deficient in chlorophyll-protein complexes. Revertant R1 was found to be identical to wild-type plants in all parameters examined (leaf color, chloroplast ultrastructure, chlorophyll-protein complexes, chlorophyll-protein complex polypeptides) except in chlorophyll content. It did not show an increased chlorophyll and carotenoid content as did the wild-type plants when exposed to high light. Revertants R2 and R3 were similar to the heterozygous mutant Su/su in most of the parameters examined. They yellowed because of a loss of chlorophyll and an increase in the amount of carotenoids, had agranal chloroplasts, and had variant chlorophyll-protein complexes when grown under high light intensities. However, each appeared to contain some of the light-harvesting pigment-protein complex polypeptides found to be absent in Su/su when grown under high-light conditions.