Methyl Jasmonate Affects O₃-inhibition of Photosynthesis and Ascorbic Acid Content in Paddy Rice Grown at Different CO₂ Concentrations

Abstract

To evaluate the role of methyl jasmonate (MeJA) on ozone (O₃: 0, 0.1, 0.3 cm³ m⁻³; abbreviated respectively as O⁰, O^0.1 and O^0.3)-induced photosynthetic inhibition of rice leaves at different atmospheric carbon dioxide (CO₂) concentrations (400 and 800 cm³ m⁻³; abbreviated respectively as C⁴⁰⁰ and C⁸⁰⁰), MeJA solutions (0, 10, 100 μM; abbreviated respectively as M⁰, M¹⁰, and M¹⁰⁰) were applied one day before acute exposure (5 h) of O₃. 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) O₃ exposure. The net photosynthetic rate (P_N), and maximum (F_v/ F_m) and operating (F_q′/F_m′) quantum efficiencies of photosystem II (PSII) were decreased by O₃ exposure at AE-0. However, MeJA ameliorated the O₃-inhibition of F_v/F_m and F_q′/F_m′ of PS II. Rapid recovery from O₃-inhibition of P_N was observed as a result of MeJA application, but MeJA decreased the P_N and stomatal conductance (g_s) at AE-0. The O₃ decreased the total ascorbic acid content, although the MeJA increased it. The effects of MeJA on the O₃-inhibition of PSII and ascorbic acid content at C⁸⁰⁰ were less than at C⁴⁰⁰.