Exogenous Application of Methyl Jasmonate at the Booting Stage Improves Rice’s Heat Tolerance by Enhancing Antioxidant and Photosynthetic Activities

With the intensification of global warming, high temperatures during rice’s growth and development could further lead to a deterioration in rice yields. Therefore, it is particularly important to further clarify the response of the rice booting stage to high temperatures, and to explore reasonable countermeasures on this basis to reduce yield losses. Methyl jasmonate (MeJA) is a derivative of jasmonates and is widely used for stress resistance. However, the role of MeJA in alleviating high temperatures during the rice booting stage has not been given enough attention. This study aimed to further evaluate the alleviation effect of methyl jasmonate on high-temperature stress during the key growth period of local conventional japonica rice. The results showed that high temperatures (37.5 °C/27.0 °C) at the booting stage had a significant impact on the antioxidant system of rice and also significantly reduced the photosynthetic capacity of the plant, resulting in a decrease in the final yields. The exogenous spraying of 0.1 mmol/L MeJA at the booting stage could effectively alleviate the influence of high-temperature stress on rice photosynthesis. Exogenous MeJA increased the stomatal conductance (Gs) of rice leaves under high-temperature stress, and correspondingly increased the transpiration rate (Tr) and decreased the organ temperature of rice plants, thereby reducing the damage to the actual photochemical efficiency (ΦPSII) caused by high temperatures. By increasing the carotenoid content (Car) and reducing the malondialdehyde content (MDA), the antioxidant capacity of the plants was restored to a certain extent under exogenous MeJA, and the yield factor showed an increase in the number of grains per panicle and the seed-setting rate of Wuyunjing 24, which alleviated the booting stage yield losses induced by high-temperature stress. In conclusion, the application of exogenous MeJA at the booting stage alleviated the negative consequences of high temperatures by enhancing the plants’ antioxidant and photosynthetic capacity. Therefore, MeJA may have a potential role in mitigating the challenges of global warming in rice production.