Modulation of 2-Acetyl-1-pyrroline (2-AP) Accumulation, Yield Formation and Antioxidant Attributes in Fragrant Rice by Exogenous Methylglyoxal (MG) Application

Pot experiments were conducted to investigate the physiological and biochemical effect of exogenous MG application on two fragrant rice cultivars, Meixiangzhan and Yuxiangyouzhan. The MG application included four treatments: 1 mmol·L –1 (MG1), 5 mmol·L –1 (MG5), and 10 mmol·L –1 (MG10), and deionized water as control (MG0). Results indicated that MG1 significantly increased the yield by 11.54–14.06% through promoting the seed-setting rate. Increases on grain 2-acetyl-1-pyrroline (2-AP) content at maturity were found in MG1. The contents of proline, Δ1-pyrrolin-5-carboxylic acid (P5C), pyrroline, and MG, and the activities of proline dehydrogenase (PDH), ornithine aminotransferase (OAT), and Δ1-pyrrolin-5-carboxylate synthase (P5CS) in plant tissues at all sampling stage were also increased in MG1 than MG0. In addition, although the malondialdehyde (MDA) content at all sampling stage was increased by MG application, MG1 increased the antioxidant enzyme activities and soluble protein content in all plant tissues and the pigment content in leaves. However, high-level MG (10 mmol·L –1 ) application significantly decreased the yield and grain 2-AP content. Overall, this study suggested that exogenous MG application regulated the 2-AP accumulation, yield formation, and antioxidant attributes in fragrant rice, and that MG application at the concentration of 1 mmol·L –1 increased the 2-AP content.