Abstract
Ribulose 1,5-bisphosphate carboxylase/oxygenase (RuBisCO) is a key enzyme in photosynthetic CO2 fixation. In higher plants, RuBisCO is a multimeric enzyme composed of large and small subunits encoded by the chloroplast rbcL gene and nuclear rbcS genes. RuBisCO is biosynthesized via complex processes, hence overall mechanism is still unknown. To understand the molecular mechanism for these processes, we have designed a positive method for screening RuBisCO biosynthesis mutants using methionine sulfoximine (MSX) which is an inhibitor of glutamine synthetase. Wild-type plants treated with MSX could not survive because photorespiratory NH3 accumulated massively depending on RuBisCO oxygenase activity. In contrast, rca mutants which lacked the activation of RuBisCO could survive under the same condition. After screened of 11000 EMS mutagenized seedlings, we obtained eight mutants which show either decreased RuBisCO amounts or low activities. These results indicate that this system is useful for screening of RuBisCO biosynthesis mutants.
