Exogenous IAA Alleviates Arsenic Toxicity to Rice and Reduces Arsenic Accumulation in Rice Grains

Arsenic (As) contamination in paddy soil reduces rice production and quality. It is important to increase the As tolerance of rice and reduce As accumulation in rice using exogenous methods. We examined the effects of exogenous plant hormones on the growth of and As accumulation in rice exposed to As. Under hydroponic conditions, 10 μmol L−1 As inhibited the growth of rice seedling. However, pretreatments with indole-3-acetic acid (IAA), salicylic acid (SA), and gibberellins (GA) rescued this inhibition, as evidenced by changes in plant morphology (root and shoot elongation, biomass, total root length, root surface area, root volume, and root tip number) and root activities, especially with the application of IAA. The As concentration in rice seedlings was significantly reduced. With soil culture, 20 mg L−1 IAA application significantly increased the grain biomass of both rice varieties, the 1000-grain weight and plant biomass of Mo Wang Gu Nei (MWGN), while decreased the As concentration in rice grains and total As accumulation in grains per plant. Furthermore, exogenous IAA reduced As translocation, as evidenced by lower As concentrations in upper leaves and internodes, but higher levels in lower leaves and internodes in Dong Ting Wan Xian (DTWX) after spraying with IAA compared to the control treatments. In conclusion, exogenous IAA can significantly promote rice growth and reduce As accumulation in rice grains.