Abstract
This study was conducted to evaluate the role of salicylic acid (SA) on acute ozone (O3: 0, 0.1, and 0.3 cm3 m−3; O0, O0.1 and O0.3, respectively)-induced photosynthetic inhibition of paddy rice leaves given different atmospheric carbon dioxide concentrations (CO2: 400 and 800 cm3 m−3; C400 and C800, respectively). Salicylic acid solutions (0, 0.1, and 1 mM; S0, S0.1, and S1, respectively) were applied as a pretreatment one day before O3 exposure. Gas exchange, chlorophyll fluorescence, and ascorbic acid were measured immediately before (BE), immediately after (AE-0), and 1 d and 3 d after (AE-1, AE-3) 5-h O3 exposure. The photosynthesis-related parameters, total ascorbic acid, and redox state of ascorbic acid (RDS) were decreased by O3 exposure. The O3-induced reduction of PN, ascorbic acid content, and its RDS were ameliorated by C800. Salicylic acid ameliorated the O3-inhibition of net photosynthetic rate (PN) slightly, and O3-induced depletion of total ascorbic acid and RDS substantially. SA did not increase PN in non-treated leaves (O0 plants). However, O3 exposure elevated the level of endogenous SA. These results show that SA plays a vital role in the defense response to acute O3 exposure in paddy rice. Effects of SA on O3-inhibition of PSII and ascorbic acid content were unaffected by elevated CO2 (C800).
