Effects of L-glutamic acid application on yield, grain quality, photosynthetic pigments, 2-acetyl-1-pyrroline, and antioxidant system of aromatic rice

Glutamic acid is a multifunctional amino acid in plants, which can be used as fertilizer to improve growth and yield of crops. However, there has been no report on foliar application of L-glutamic acid in rice production. In this study, we hypothesized that foliar application of L-glutamic acid could increase yield and improve grain quality of aromatic rice. A three-year field experiment was conducted from 2019 to 2021 with five L-glutamic acid treatments (0.00 (CK), 0.25 (Glu0.25), 0.50 (Glu0.50), 1.00 (Glu1.00), 2.00 (Glu2.00) g L−1) foliar applied at the heading stage. The leaves were sampled four days after receiving treatments, and physiological and biochemical indexes were determined. Grain yield, yield-related traits, and grain quality attributes were measured. Compared with CK, Glu0.50, Glu1.00, and Glu2.00 treatments significantly increased grain yield by 5.11–7.41%, 11.20–26.36%, and 10.61–15.34%, respectively. Higher seed-setting rates were recorded in Glu0.50, Glu1.00, and Glu2.00 treatments than CK. Glu1.00 treatment increased the contents of total chlorophyll, chlorophyll a, chlorophyll b, and carotenoid in leaves compared with CK. Higher activities of peroxidase and superoxide dismutase and lower malonaldehyde content in leaves were observed in Glu1.00 treatment than CK. Moreover, compared with CK, Glu0.50, Glu1.00, and Glu2.00 treatments increased grain protein content by 3.36–4.78%, 7.11–11.34%, and 2.38–4.78%, respectively. However, L-glutamic acid treatments had no significant effect on the grain 2-acetyl-1-pyrroline content. In conclusion, foliar application of L-glutamic acid at suitable concentrations increased photosynthetic pigments, grain yield, and grain protein content of aromatic rice. Our study would provide new and more information for aromatic rice cultivation as well as L-glutamic acid application in agriculture.