Distinct cadmium detoxicity response between rice cultivars carrying functional or loss-of-function OsHMA3 allele

Abstract

Plants encounter various abiotic stress during their growth, making it essential to understand their responses to such challenges. Though function of OsHMA3 in cadmium (Cd) sequestration into rice root vacuoles has been well characterized, little is known about how different OsHMA3 alleles influence plant responses to high Cd exposure. In this study, we utilized rice cultivars carrying a functional OsHMA3 allele (9311) and a loss-of-function OsHMA3 allele (W4) to investigate their differences in Cd detoxification responses. Morphological, physiological and subcellular changes, as well as Cd species were analyzed. The results indicated that Cd was more extensively transported to shoots in W4 than 9311 as expected. However, W4 exhibited a more pronounced growth inhibition with reductions in shoot and root length, more severe leaf chlorosis with chlorophyll a, b, and carotenoid levels decreased by 31%, 43%, and 45% in W4, respectively, while no significant reductions were observed in 9311. Enhanced cell ultrastructural damage, including membranolytic changes, nuclear membrane lysis, and damage to the nucleus, was noted in W4, while, relatively normal cell structure in 9311. The antioxidant enzyme systems exhibited greater responses in W4 than those in 9311. Additionally, lower levels of nitrate/nitrite, chloride, and aminophenol Cd forms were found in W4 roots, while higher concentrations of these were observed in shoots, indicating distinct Cd detoxicity response between W4 and 9311. This study underscores the significance of the OsHMA3 gene in Cd detoxification responses, offering valuable insights into the mechanisms of plant Cd detoxification. 1. Rice cultivar with loss-of-function OsHMA3 allele showed greater Cd sensitivity, more severe growth inhibition and leaf chlorosis under Cd toxicity, and leaf chlorosis were induced by Cd toxicity, irrespective of Fe content. 2. More severe Cd toxicity as indicated by oxidative response and cell ultrastructure changes in rice shoot were observed in OsHMA3 function missing cultivar. 3. Significant positive correlation between Cd toxicity and shoot Cd content were observed, which was closely related with OsHMA3 function.