Responses of yield formation and anthocyanin biosynthesis of red rice to salt stress

Anthocyanin is an important antioxidant and anti-inflammatory substance in red rice. However, effects of salt stess on anthocyanins in red rice and its regulation mechanism have been scarcely reported. The Field experiment comprised three irrigation treatments i.e., freshwater irrigation (CK) and brine irrigation i.e., salinity of 2.0‰ (T1) and salinity of 4.0‰ (T2) and two red rice varieties i.e., Youxianghongdao (YXHD) and Tiandaohong2 (TDH2). Our results demonstrated that brine irrigation significantly reduced grain yield and dry matter accumulation, but substantially enhanced the anthocyanin content in red rice grains. The targeted metabolismics of anthocyanins identified four anthocyanins in red rice grains, including Cyanidin−3-O-(6"-O-coumaryl) galactoside, Delphinidin−3-O-(6"-O-xylosyl) glucoside, Peonidin−3-O-(acetyl)(malonyl) galactoside, Peonidin−3-O-(6"-O-acetyl-malonyl) glucoside), and the glycosyl might determine the stable accumulation of anthocyanin in red rice grains under brine irrigation. The precursors and enzymes involved in anthocyanins biosynthesis, i.e., soluble sugar, naringenin, phenylalanine, phenylalanine ammonia lyase, 4-coumaroyl-CoA ligase, and other related enzymes, which were substantially improved by the application of brine water. Correspondingly, the differentially expressed genes were significantly enriched in phenylpropanoid biosynthesis and starch and sucrose metabolism. Furthermore, brine irrigation significantly up-regulated the gene expression of phenylalanine ammonia lyase and 4-acyl-CoA ligase in phenylpropanoid synthesis, but inhibited the expression of genes related to starch and lignin synthesis to regulate anthocyanin biosynthesis. In conclusion, brine irrigation increased anthocyanin content in red rice. Our results provide a new application way for improving the anthocyanin content of red rice by adjusting the salt concentration of brine irrigation.