This study aimed to determine the mechanism of exogenous melatonin application in alleviating the combined Pb and Cd (Pb-Cd) toxicity on aromatic rice (Oryza sativa L.). In this study, a pot experiment was conducted; two aromatic rice varieties, Yuxiangyouzhan and Xiangyaxiangzhan, were selected, and sprays using 50, 100, 200, and 400 μmol L⁻¹ melatonin (denoted as S50, S100, S200, and S400) and irrigation using 100, 300, and 500 μmol L⁻¹ melatonin (denoted as R100, R300, and R500) were also selected. The results showed that, under the S50, S100, and S200 treatments, the Pb content of aromatic rice grain decreased, and the grain yield increased significantly. Moreover, the application of exogenous melatonin significantly reduced the accumulation of H₂O₂ in rice leaves at maturity under Cd–Pb stress and reduced the MDA content in Xiangyaxiangzhan leaves. In addition, the microbial community structure changed significantly under S50 and R300 treatments. Some pathways, such as the synthesis of various amino acids and alanine, aspartate, and glutamate metabolism, were regulated by S50 treatment. Overall, melatonin application improved aromatic rice grain yield while reducing heavy metal accumulation by regulating the antioxidant capacity and metabolites in aromatic rice plants and altering the physicochemical properties and microbial community structures of the soil.

The present study investigated the dynamic changes in vitamin E and gene expression within its biosynthetic pathway during three germination periods of four brown rice cultivars with different seed coat colors. The results reveal that the vitamin E content increased during the germination process of all brown rice cultivars. Moreover, the content of α-tocopherol, α-tocotrienol, and β-tocopherol significantly increased at the later stage of germination. The expression levels of DXS1 and γ-TMT genes in all cultivars were significantly increased, whilst the HGGT gene expression levels of G6 and XY cultivars increased significantly at the later stage of brown rice germination. In addition, the expression levels of MPBQ/MT2 in G1 and G6 cultivars, and TC expression levels in G2 and G6 cultivars were substantially increased at the later stage of germination. Overall, the up-regulation of MPBQ/MT2, γ-TMT, and TC genes doubled the content of α-tocopherol, α-tocotrienol, and β-tocopherol, and the total vitamin E content of brown rice was at its highest at 96HAT. The utilization of the germination period can effectively improve the nutritional value of brown rice, which can be used for the development and utilization of brown rice for healthy rice products.

The mechanized seed production of hybrid rice (Oryza sativa L.) represents significant progress in modern agriculture. However, the technologies and the crop management strategies in mechanized hybrid rice seed production are still immature. The present study was conducted with three field experiments to explore the effects of different planting densities, the flight height of an agricultural unmanned aerial vehicle (AUAV) for assisting the pollination, fertilization techniques, and the row-ratio of the restore line and the sterile line on seed yield in hybrid rice seed production. In experiment 1, three planting densities “DS1: 250000 hills per ha; DS2: 285000 hills per ha; DS3: 3,33,000 hills per ha” and three flight heights of an AUAV (FH1: above ground 2 m; FH2: above ground 3 m; FH3: above ground 4 m) were adopted. The results showed that DS1 and DS2 treatments produced a higher seed yield than the DS3 treatment, and the seed yield in the FH2 treatment was significantly higher than FH1 and FH3. In experiment 2, two fertilizer application methods, mechanized deep placement of fertilizer and traditional manual broadcasted fertilizer, were adopted. The results showed that deep placement of fertilizer significantly increased seed yield by increasing the effective panicle number and the grain number per panicle. In experiment 3, three row-ratios of sterile line and restore line at 8:1 (R1), 9:1 (R2), 10:1(R3) were adopted, and the highest seed yield was recorded in the R1 treatment.