Mungbean leaves of varying age at three growth stages of plant were subjected to ambient (330 μl l-1), 600 and 900 μl l-1 carbon dioxide for a period of five hours. Time course changes in net carbon dioxide exchange rate (NCER) and activities of RuBP carboxylase, glycolate oxidase and nitrate reductase were studied in the CO2 enriched leaves. Leaves at different insertion levels as well as of different age responded differently to CO2 concentration. Leaves formed earlier at lower insertion level responded better compared to leaf of the same age formed at upper insertion level. No response of RuBP carboxylase in vitro to enriched CO2 indicates the possibility of its non-participation in enzyme regulation. There was partial suppression of glycolate oxidase activity, increase in nitrate reductase while no response in RuBP carboxylase was observed at higher CO2 concentration.
