Rubisco expression in rice leaves is related to genotypic variation of photosynthesis under elevated growth CO2 and temperature

Genetic modifications of agronomic crops will likely be necessary to cope with global climate change. This study tested the hypotheses that genotypic differences in rice (Oryza sativa L.) leaf photosynthesis at elevated [CO2] and temperature are related to protein and gene expression of Rubisco, and that high growth temperatures under elevated [CO2] negatively affect photosystem II (PSII) photochemical efficiency. Two rice cultivars representing an indica (cv. IR72) and japonica type (cv. M103) were grown in 350 (ambient) and 700 (elevated) mumol CO2 mol(-1) at 28/18, 34/24 and 40/30degreesC sinusoidal maximum/minimum, day/night temperatures in outdoor, sunlit, environment-controlled chambers. Leaf photosynthesis of IR72 favoured higher growth temperatures more than M103. Rubisco total activity and protein content were negatively affected in both genotypes by high temperatures and elevated CO2. However, at moderate to high growth temperatures, IR72 leaves averaged 71 and 39% more rbcS transcripts than M103 under ambient and elevated CO2, respectively, and likewise had greater Rubisco activity and protein content. Expression of psbA (D1 protein of PSII) in IR72 leaves increased with temperature, whereas it remained constant for M103, except for a 20% decline at 40/30degreesC under elevated CO2. Even at the highest growth temperatures, PSII photochemical efficiency was not impaired in either genotype grown under either ambient or elevated CO2. Genotypic differences exist in rice for carboxylation responses to elevated CO2 and high temperatures, which may be useful in developing genotypes suited to cope with global climate changes.