EFFECT OF CO2 CONCENTRATION ON CARBONIC-ANHYDRASE AND RIBULOSE-1,5-BIPHOSPHATE CARBOXYLASE OXYGENASE EXPRESSION IN PEA/

The effect of external CO2 concentration on the expression of carbonic anhydrase (CA) and ribulose-1,5-bisphosphate carboxylase/oxygenase (R ubisco) was examined in pea (Pisum sativum cv Little Marvel) leaves. E nzyme activities and their transcript levels were reduced in plants gr own at 1000 mu L/L CO2 compared with plants grown in ambient air. Grow th at 160 mu L/L CO2 also appeared to reduce steady-state transcript l evels for rbcS, the gene encoding the small subunit of Rubisco, and fo r ca, the gene encoding CA; however, rbcS transcripts were reduced to a greater extent at this concentration. Rubisco activity was slightly lower in plants grown at 160 mu L/L CO2, and CA activity was significa ntly higher than that observed in air-grown plants. Transfer of plants from 1000 mu L/L to air levels of CO2 resulted in a rapid increase in both ca and rbcS transcript abundance in fully expanded leaves, follo wed by an increase in enzyme activity. Plants transferred from air to high-CO2 concentrations appeared to modulate transcript abundance and enzyme activity less quickly. Foliar carbohydrate levels were also exa mined in plants grown continuously at high and ambient CO2, and follow ing changes in growth conditions that rapidly altered ca and rbcS tran script abundance and enzyme activities.