Modulation of Antioxidant Attributes and Grain Yield in Fragrant Rice by Exogenous Cu Application

Despite copper (Cu) being an essential nutrient for the growth and development of all living organisms, the yield and tolerance mechanisms of fragrant rice under Cu-induced stress have not been reported. In this study, we tested two fragrant rice cultivars (Meixiangzhan and Yuxiangyouzhan) at the heading stage, with four Cu doses (CuSO 4 ·5H 2 O), i.e., 0 (CK), 20 (T1), 40 (T2), and 60 mM (T3) in a pot experiment. Our results showed that T2 treatment improved the yield of Meixiangzhan and Yuxiangyouzhan by 8.33% and 18.51%, respectively, by improving grains per panicle and the seed-setting rate. Moreover, Yuxiangyouzhan had the highest yield in T2 treatment, indicating that it had better Cu-tolerance than Meixiangzhan. Both cultivars had a similar response to Cu dose treatments. While T1 and T2 improved leaf pigment contents, antioxidant enzyme activities, and soluble protein content in plant tissues, T3 treatment instead promoted higher malondialdehyde (MDA) content accumulation and regulated antioxidant attributes. Overall, low-level Cu dosing significantly improved the fragrant rice yield via modulation of the antioxidant attributes. Therefore, this study provides supporting evidence for utilizing Cu reagent or assessing Cu toxicity in fragrant rice.