Abstract
Chloroplastic 2-oxoglutarate/malate transporter (OMT) functions in mediating between carbon and nitrogen metabolic pathways. Additionally, we estimated that OMT also functions as an oxaloacetate transporter. Now we examined the uptake activity of oxaloacetic acid (OAA) in chloroplasts. It showed that chloroplasts of omt1-T2 had lower affinity for OAA than that of wild type. The addition of OAA rapidly lowered the high NADP-MDH activation state due to drive of malate valve. However the extent of the decrease was lower in omt1-T2 chloroplasts. These data indicate that the reduction of OAA uptake activity in omt1-T2 chloroplasts leads to deteriorate the malate valve function. Furthermore, omt1-T2 plants accumulated less Ser and Gly, and more glyoxylate than wild type. Therefore, the photorespiration rate was thought to be declined in omt1-T2 plants. The present results indicate a crucial role of OMT in avoiding photoinhibition by regulating malate valve and photorespiration.
