The phospholipid-deficient pho1 mutant of Arabidopsis thaliana is affectedin the organization, but not in the light acclimation, of the thylakoid membrane

The pho1 mutant of Arabidopsis has been shown to respond to the phosphate d eficiency in the leaves by decreasing the amount of phosphatidylglycerol (P G). PG is thought to be of crucial importance for the organization and func tion of the thylakoid membrane. This prompted us to ask what the consequenc es of the PG deficiency may be in the pho1 mutant when grown under low or h igh light. While in the wild-type, the lipid pattern was almost insensitive to changes in the growth light, PG was reduced to 45% under low light in t he mutant, and it decreased further to 35% under high light. Concomitantly, sulfoquinovosyl diacylglycerol (SQDG) and to a lesser extent digalactosyl diacylglycerol (DGDG) increased. The SQDG increase correlated with increase d amounts of the SQD1 protein, an indicator for an actively mediated proces s. Despite of alterations in the ultrastructure, mutant thylakoids showed v irtually no effects on photosynthetic electron transfer, O-2 evolution and excitation energy allocation to the reaction centers. Our results support t he idea that PG deficiency can at least partially be compensated for by the anionic lipid SQDG and the not charged lipid DGDG, This seems to be an imp ortant strategy to maintain an optimal thylakoid lipid milieu for vital pro cesses, such as photosynthesis, under a restricted phosphate availability. (C) 1998 Elsevier Science B.V. All rights reserved.