Effects of O3 and CO2 on photosystem II, nitrate reductase and nitrite reductase in paddy rice leaves

Abstract

To evaluate the interaction between O3 and CO2 on photosynthesis and nitrogen metabolism in rice, combined exposures of O 3 [0, 0.1, 0.3 cm3 m-3 (abbreviated as 0°, O0.1, O0.3)] and CO2 [400, 800 cm3 m-3 (abbreviated as C400, C800)] were applied for 5 h using environment-controlled chambers with natural-light. Subsequently, the plants were raised for 3 d under clean air (O° + C400) conditions. Immediately before (BE), immediately after (AE-0), and 1 and 3 d after (AE-1, AE-3) gas exposure, the chlorophyll fluorescence of photosystem II (PSII) and activities of nitrate (NR) and nitrite (NiR) reductase were determined. Results show that maximum (Fv/Fm) and operating (Fq'/Fm') quantum efficiencies and NiR activity were inhibited by O3, but they were ameliorated by elevated CO 2, suggesting that the Cvinhibition of photosynthesis accompanied the reduced electron transport toward the downstream of photosystem and suggesting that the reduction power became deficient. Because NiR locates in the chloroplast and uses reducing power from PSII, it must receive a greater O 3-inhibition than cytoplasmic NR does.