The reduction of amylose content in rice grain and decrease of Wx gene expression during endosperm development in response to drought stress

Rice (Oryza sativa L.) is a staple food supplying nutrition for more than half of the world’s population. Amylose content (AC) is widely considered as the most important factor determining rice grain quality for cooking, eating and processing. Field experiments of 32 rice varieties of different ecotypes grown under artificial drought stress from 30 days after transplanting to maturity and well watered control treatments were conducted on 2 locations (Huazhong Agriculture University at Wuhan, China, 30°N, 114°E, and Lingshui county, Hainan province, China, 18°N, 109°E) in 2 successive years (2006-2007) to investigate the effect of drought stress on rice grain quality. Results indicated that drought stress significantly reduced the average AC of the 32 varieties from 17.4% to 16.7% in Wuhan and 17.9% to 17.4% in Hainan. There were significant interactions of genotype by drought stress (G×T), genotype by location (G×L), genotype by year (G×Y), genotype by drought stress and location (G×L×T), and genotype by drought stress and year (G×T×Y) for AC. Pot experiment using PVC cylinders on 2 varieties (one japonica and one indica rice) was carried out at Huazhong Agriculture University to study the genetic basis for the reduction of AC caused by drought stress (2008). Spikelets of plants under drought stress and control were sampled at 5, 10, 15, 20 and 25 days after flowering for the measurement of AC and quantitative real-time RTPCR assay of Wx gene expression in developing endosperms. Results showed that drought stress led to the decrease of AC and lower expression level of Wx gene from the early stage of grain filling to the maturity in the developing endosperms. It suggests that the drought stress during grain filling has negative effect on Wx gene expression, which tends to reduce the accumulation rate of amylose in the endosperm and result in lower AC in rice grain.