Physiological and Biochemical Attributes of Chromium Detoxification are Regulated by Root synthesized Organic Acids in Rice Varieties

Abstract

To know effective physiological response against chromium toxicity, 25 rice varieties were cultivated on the hydroponic solution treated with 100µM chromium and physiological as well as biochemical features were evaluated compared with non-treated control plants. In this investigation, it was found that the concentration of citric acid synthesized and secreted by roots influences the mitigation of chromium toxicity. In varieties BR-58, BR-63 and BR-68 chromium uptake were significantly higher than the control plant but their translocation to shoot was restricted indicating elevated Cr retention in roots. This retention was facilitated by root secreted citric acid which was assured by significant rhizospheric pH reduction (15%, 18.5% and 20.9% respectively) under chromium stress. Furthermore, BR-73 showed an efficient exclusion mechanism keeping down metal uptake by citric acid ensured by 15% rhizosphere pH reduction. In contrast, varieties of rhizospheres with a pH reduction of less than 10% were unable to withstand chromium toxicity. The findings indicate that a reduction of 15% or more in rhizospheric pH serves as the benchmark for the necessary level of organic acid secretion required for chromium tolerance. Moreover, the strategies employed for tolerance differ based on genotypes rather than species. Furthermore, it offers an efficient screening technique for metal tolerant rice plants.