CO2 enrichment delays a rapid, drought-induced decrease in Rubisco small subunit transcript abundance

Rice (Oryza sativa L. cv. IR-72) was grown in sunlit chambers at 350 and 70 0 mu mol CO2 mol(-1) under conditions of continuous flooding (control) or d rought which was imposed at panicle initiation, to evaluate the effects of CO2 enrichment and soil water deficit on photosynthesis and Rubisco gene ex pression. Leaf and canopy photosynthetic rates were enhanced by high [CO2] but reduced by drought. High [CO2] and severe drought both reduced rbcS tra nscript abundance, along with the activity, activation and protein content of Rubisco, but the K-m (CO2) was not affected. The transition from moderat e to severe drought caused a rapid decline, within 24 h, in the rbcS transc ript abundance. High [CO2], however, delayed the adverse effects of severe drought on rbcS transcript abundance and activities of Rubisco, and permitt ed photosynthesis to continue for an extra day during the drought-stress cy cle.