Abstract
On the reducing side of photosystem I (PSI), electrons are distributed into several pathways; reduction of NADP+ and PQ as liner and cyclic electron transports, respectively, and transfer of reducing power to amino acid metabolic pathway. To characterize electron transfer reaction around PSI, we screened Arabidopsis mutants that show a slow or no decay kinetics of fluorescence yield from the peak Fp and isolated several mutants from an EMS-treated M2 population. Of these mutants, two lines 32-33 and 7-2-33 showed a slower decrease in fluorescence yield, and were subjected to conventional map-based cloning. Both lines were found to have a mutation causing amino acid substitution in the GUL1 gene, coding for ferredoxin-dependent glutamate synthase (Fd-GOGAT). Overexpression of Fd-GOGAT rescued the defective fluorescence induction kinetics as well as the pale-leaf phenotype of 32-33, confirming that GUL1 is responsible for these phenotypes in 32-33. Immunoblot analyses revealed that 32-33 accumulates Fd-GOGAT at 25% of WT level, with the slightly retarded electrophoretic mobility. Studies on the kinetics of the redox rate of P700 are underway in 32-33.
