Riboflavin improves grain yield, 2-acetyl-1-pyrroline accumulation, and antioxidative properties of fragrant rice.

BACKGROUND: Riboflavin, a vital water-soluble vitamin with antioxidative activity, plays a critical role in maintaining overall bodily health and defense responses. However, its impact on fragrant rice yield and aroma remains unexplored. RESULTS: In a 2022 pot experiment with Meixiangzhan and Yuxiangyouzhan fragrant rice cultivars, we applied riboflavin foliar treatments at concentrations of 0 (CK), 10 (R10), 20 (R20), and 40 (R40) mg L-1 during the initial heading stage. Riboflavin increased rice yield, 2-acetyl-1-pyrroline (2-AP) content, and antioxidative properties. It boosted 2-AP level by 13.1-50.1% for Meixiangzhan and 22.3-35.3% for Yuxiangyouzhan, with the highest levels in R20 and R10 treatments. This increase is significantly correlated with elevated levels of proline, pyrroline-5-carboxylic acid, pyrroline, and methylglyoxal, as well as heightened enzyme activities, including those of proline dehydrogenase, ornithine aminotransferase, and pyrroline-5-carboxylic acid synthetase (P5CS). The R20 treatment resulted in the highest yield due to an improved seed-setting rate. Importantly, a positive correlation emerged between 2-AP content and yield, both significantly linked to superoxide dismutase, proline, hydrogen peroxide, P5CS, catalase, and pyrroline. CONCLUSION: Riboflavin maintained enzyme activities, regulated substance synthesis pathways, and increased 2-AP and yield, especially in the R20 treatment. These insights advance fragrant rice production theory by uncovering riboflavin's role in the development of fragrant rice. © 2023 Society of Chemical Industry.

Foliar methyl jasmonate (MeJA) application increased 2-acetyl-1-Pyrroline (2-AP) content and modulated antioxidant attributes and yield formation in fragrant rice.

Endogenous methyl jasmonate (MeJA) mediates abiotic and biotic stresses in plants. Exogenous MeJA application can stimulate and defend plant gene expression and induce plant chemical defense. The effects of foliar MeJA application on yield and 2-acetyl-1-pyrroline (2-AP) biosynthesis of fragrant rice are scarcely investigated. The pot experiment was conducted by spraying different concentrations of MeJA (0, 1, and 2 µM; denoted as CK, MeJA-1, and MeJA-2) at the initial heading stage of two fragrant rice cultivars, Meixiangzhan and Yuxiangyouzhan. The results showed that foliar MeJA application significantly increased the grain 2-AP content by 32.1% and 49.7%, respectively, following MeJA-1 and MeJA-2 treatments, and the two cultivars showed the highest 2-AP content upon MeJA-2 treatment. However, the grain yield was increased in MeJA-1 as compared with MeJA-2 treatment for all rice cultivars and no significant differences were observed in yield and yield-related traits compared with CK. The aroma was improved by foliar MeJA application which was strongly associated with the regulation of the precursors and enzymes involved in 2-AP biosynthesis. In particular, the contents of proline, pyrroline-5-carboxylic acid, and pyrroline at maturity, as well as the activities of proline dehydrogenase, ornithine aminotransferase, and pyrroline-5-carboxylic acid synthetase, were positively correlated with grain 2-AP content. On the other hand, foliar MeJA application improved the contents of soluble protein, chlorophyll a and b, and carotenoid, and increased the activity of antioxidant enzymes. Moreover, peroxidase activity and leaf chlorophyll contents were significantly positively correlated to 2-AP content following foliar MeJA application. Therefore, our results implied that foliar MeJA application increased aroma and influenced yield by regulating the physio-biochemistry characters and resistance, and suggested that the optimal concentration of MeJA for the best positive effect on the yield and aroma was 1 µM. However, further study is required to evaluate the metabolic level and molecular basis of the regulatory mechanism of foliar MeJA application on 2-AP in fragrant rice.

Effect of foliar copper application on grain yield, 2-acetyl-1-Pyrroline and copper content in fragrant rice.

Literature reporting the effects of application of exogenous copper (Cu) on the grain yield, 2-acetyl-1-pyrroline (2-AP) and Cu content of fragrant rice is scarce. Pot experiments were conducted in early and later season in 2020 with two fragrant rice cultivars, Meixiangzhan and Yuxiangyouzhan, at heading stage using four treatments, i.e.: 0 (CK), 20 (T1), 40 (T2), and 60 mM (T3) CuSO4·5H2O to assess the effects of foliar copper application on the yield, 2-AP and Cu content. Results showed that T2 treatment improved the yield of Meixiangzhan and Yuxiangyouzhan by 6.88% and 11.35% respectively, by increased seed-setting rate. Meanwhile, T2 treatment greatly increased the grains 2-AP content by 21.95% and 10.15% in early season, and by 5.40% and 27.25% in later season, respectively, which was significant associated with the contents of proline, pyrroline-5-carboxylic acid (P5C) and pyrroline, and the activities of proline dehydrogenase (PDH), ornithine aminotransferase (OAT) and pyrroline-5-carboxylic acid synthetase (P5CS). Foliar copper application increased the grain Cu content and showed the highest values in T3 treatment. Overall, foliar copper application at heading stage had a positive effect on yield and grain 2-AP and Cu content of fragrant rice. The results from this study show that T2 treatment (moderate CuSO4 application) had the most desirable outcomes, synergistically improving the yield and aroma of fragrant rice as well as enriching the grain copper content.

Ultrasonic seed treatment improved physiological and yield traits of rice under lead toxicity.

Lead (Pb) is a highly toxic metal that damages normal plant metabolism and often results in reduced crop growth and yield. To measure whether or not ultrasonic seed (US) treatment alleviates Pb stress in rice, the seeds of two rice cultivars, i.e., Guangyan1 and Huahang31, were exposed to 30 min of ultrasonic vibration and then the seedlings were transplanted to Pb-contaminated soil. Results revealed that the Pb contents in roots, stems, leaves, panicles (at heading), and brown rice (at maturity) were lower in US treatment than control (CK; without US treatment); the trend for accumulation of Pb in different plant parts was recorded as: root ˃ stems ˃ leaves ˃ panicles ˃ brown rice in both rice cultivars. Overall, the Pb contents in the brown rice of Huahang31 were higher than those in Guangyan1. Moreover, the contents of proline and soluble protein as well as the activities of superoxide dismutase (SOD), catalase (CAT), and ascorbate peroxidase (APX) were significantly higher while the malondialdehyde (MDA) contents were significantly reduced in US treatment compared to CK. The effective panicle number, seed set percentage, grains per panicle, 1000-grain weight, and grain yield were increased by 8.9%, 5.3%, 6.8%, 4.4%, and 26.6% in Guangyan1 and 3.2%, 5.7%, 5.7%, 5.0%, and 24.2% in Huahang31, respectively in US treatment compared to CK. Hence, seed treatment with ultrasonic waves could improve rice performance and reduce brown rice Pb accumulation under Pb-polluted soils.