Poster: Photosynthesis

Abs # 383: Mutation in the g-subunit of chloroplast ATP synthase in Arabidopsis alters the redox regulatory process and photosynthesis under the light

Presenter:	Wu, Guosheng , gwu1@uiuc.edu
Authors	Wu, Guosheng  (A)   Ort, Donald R. (A) (B)
Affiliations:	(A): Department of Plant Biology, University of Illinois at Urbana-Champaign, Urbana, IL 61801 (B): Photosynthesis Research Unit, USDA/Agricultural Research Service, Urbana, IL 61801

The g-subunit of chloroplast ATP synthase contains a redox regulatory domain through which ATP synthase activity is regulated during diurnal cycles of light by dithiols and disulfide exchange between thioredoxin and the g-subunit. The cfq mutant has a point mutation in the downstream of g-subunit regulatory domain, in which the Glu244 is substituted by Lysine. In this experiment, the fresh chloroplasts were used to study the change of the mutant ATP synthase behaviors. The ATPase activity of cfq is slightly responsive to the light induction, but the wild-type ATPase activity increased significantly and reached its maximum (more than 2 folds) under the light of 50 mmol m^-2 s^-1 indicating the inability of light activation of the mutated enzyme. The experiment of ATP synthetic activity showed that the ATP synthetic activity of cfq is also lower than that of wild-type at any light level, further indicating that the mutation in the g-subunit greatly impairs the light motivated activation of ATP synthase. But the fact that, in the cfq mutant, the ATP synthetic activity increased significantly under the light with a peak at 800 mmol m^-2 s^-1 demonstrates that the mutated enzyme can be activated by the proton potential across the thylakoid membrane in spite of loss of redox modulation. The light induction of steady-state CO₂ exchange experiments show that the photosynthesis rate of cfq is about 20% lower than that of wild-type and it takes longer time to reach full induction.