DIFFERENTIATION OF PHYSIOLOGICAL RESPONSES BETWEEN HIGH SALT TOLERANCE SEA RICE AND HYBRID RICE TO CO-EXPOSURE OF CERIUM OXIDE NANOPARTICLES AND SODIUM CHLORIDE

In this study, we investigated the physiological responses of high salt tolerate sea rice to co-exposure of cerium oxide nanoparticles (CeO2 NPs) and sodium chloride (NaCl) environment. Rice seedlings were cultured in nutrient solution amended with different exposure doses of CeO2 NPs (0-2000 mg/L) and 100 mM NaCl. The rice fresh biomass was significantly decreased in the salt stress. Plant height, root length, and plant biomass showed a slight drop in lower NPs exposure doses (20 and 200mg/L), but increased in a higher concentration, especially for hybrid rice. Scanning electron microscope (SEM) images indicated that the length and the distance between stomata of hybrid rice were more stable under salt stress. The stomata area of two cultivars changed similarly with the changes of CeO2 NPs. The area of the stomata on positive side of leaves was larger at lower concentration (20 mg/L) and became smaller at higher concentration (2000 mg/L). In addition, Ce and Fe accumulation in both rice shoots exhibited a dose-dependent manner with increasing the concentrations of CeO2 NPs. Lower concentrations of CeO2 NPs reduced the salt toxicity as determined by Na+/K+ ratio; while higher concentrations of CeO2 NPs strengthened the toxic effect. The contents of IAA, BR and GA4 were substantially increased significantly under salt stress. IAA content in sea rice seedlings decreased with the increase of CeO2 NPs concentration, while the change of GA4 was reversed. The BR content was stable under double stress, and the change of GA4 in hybrid rice was opposite to that of sea rice. Our results could provide useful information for understanding the physiological responses and possible mechanisms of two cultivars of rice to co-exposure of CeO2 NPs and NaCl.