Phytochelatin- and metallothionein-mediated detoxification of gallium in rice seedlings

Gallium (Ga) is an emerging chemical pollutant associated with high-tech industries. This study investigated detoxification of Ga in rice seedlings through chelation pathway by metallothioneins (MTs) and phytochelatins (PCs), and ROS scavenging process by MTs. The relative growth rate (RGR) and water use efficiency (WUE) of rice seedlings were notably decreased by Ga stress. More Ga accumulation was detected in roots compared to shoots, with considerable variation in subcellular compartments. Fold changes of H 2 O 2 and O 2 -• in rice tissues were greater in roots compared to shoots. Results from the mixed modeling indicated that the accumulation of ROS in roots caused more damage on the rice plants than Ga accumulation, while accumulation of Ga in shoots resulted in more negative consequence than ROS accumulation. Most genes associated with phytochelatins synthase (PCS) down-regualted, suggesting inactivation of PCS in the synthesis of PCs in rice roots under Ga exposure. Down-regulation of OsMT2c was observed under Ga stress, suggesting its involvement in MT-mediated chelation to Ga ions. Importantly, positive expression of OsMT1a , OsMT1d , OsMT1f , OsMT1g , OsMT2a , and OsMT2b , exhibited closer correlation to accumulation of ROS in rice plants imposed by Ga stress. These results reveal that chelation of Ga ions to MTs was highly involved, while the PC-mediated chelation to Ga ions in rice roots was negligible. Up-regulation of OsMT genes capable of scavenging ROS suggests their activation in minimizing oxidative stress. These findings provide valuable insights for elucidating the roles of PCs and MTs in detoxification of Ga in rice seedlings. • Ga accumulation led to a significant alteration in the RGR and WUE of rice plants. • Accumulation of H 2 O 2 and O 2 -• in Ga-treated rice plants was observed. • Chelation of Ga ions to MTs was highly involved, while the PC-mediated chelation in rice roots is negligible. • Up-regulation of OsMT genes capable of scavenging ROS suggests their activation in minimizing oxidative stress. • The role of PCs and MTs in detoxification of Ga in rice seedlings is evident.