Phenomic and metabolomic responses of roots to cadmium reveal contrasting resistance strategies in two rice cultivars ( Oryza sativa L.)

To cope with heavy metal stress, plant root systems undergo root structure modification and release of multifarious metabolites. Elucidation of the resistance strategies to heavy metals mediated by the root system is crucial to comprehend the resistance mechanisms of plants. Here two rice cultivars with contrasting grain cadmium (Cd) accumulation traits were selected and the responses of their root systems to Cd stress were evaluated by morphological and metabolomics analysis. The phenomic and metabolomic responses of the root system varied between the two cultivars under Cd stress. The low-Cd accumulation rice cultivar (TY816) had a more highly developed root system that coped with Cd stress (10 µM) by maintaining high root activity, while the root cells of the high-Cd accumulation cultivar (JY841) lost viability due to excessive Cd accumulation. TY816 upregulated lipids and fatty acids to reduce Cd uptake, whereas JY841 upregulated phenylethanoid glycosides to cope with Cd-induced oxidative stress. The combination of metabolomics and phenomics revealed that rice roots employ multiple strategies to increase their tolerance of Cd-induced oxidative stress. Differing capacities to shape the root system architecture and reprogram root exudate metabolites may contribute to the contrasting Cd accumulation abilities between JY841 and TY816.