Managing arsenic (V) toxicity by phosphate supplementation in rice seedlings: modulations in AsA-GSH cycle and other antioxidant enzymes

The toxic and non-essential metalloid arsenic (As) is ubiquitous in the environment with its absorption from the soil into the plants' roots posing detrimental effects on the crop plants and hence the food availability and food security are also threatened. The present study was intended to reduce the As-induced toxicity in rice seedlings (Oryza sativa L.) by phosphate (PO43-). For this, three concentrations of potassium phosphate (KH2PO4), 50, 100 and 150 mu M were supplemented along with 50 mu M As exposure to hydroponically grown 7-day-old rice seedlings. Supplementation of PO43- significantly recovered arsenic-induced diminutions in growth parameters and photosynthetic pigment contents which were due to the significant increase in superoxide radical (SOR, O-2(center dot) over bar ) and hydrogen peroxide (H2O(2)). Supplementation of 50 mu M PO43- could significantly increase the activity of APX (ascorbate peroxidase) and GR (glutathione reductase) while 100 mu M PO43- could increase the activity of DHAR (dehydroascorbate reductase) and monodehydroascorbate reductase (MDHAR). As the amount of PO43- was increased, the ratio of AsA/DHA (reduced to oxidized ascorbate) and GSH/GSSG (reduced to oxidized glutathione) was increased significantly due to increase in the reduced form of the non-enzymes i.e. AsA and GSH. The activity of SOD (superoxide dismutase) and GPX (guaiacol peroxidase) decreased significantly after a substantive increase in their activities due to As stress while the CAT (catalase) activity further enhanced after the supplementation of 50 and 100 mu M PO43-. Thus, the As-induced oxidative stress in the rice seedlings was managed by concerted modulations in the activities of SOD, GPX, CAT and AsA-GSH cycle enzymes and metabolites.

Automated summary

The study aimed to reduce arsenic-induced toxicity in rice seedlings through phosphate supplementation, which significantly recovered diminished growth parameters and photosynthetic pigment contents. The activities of various enzymes in the AsA-GSH cycle were modulated to manage oxidative stress in rice seedlings caused by arsenic exposure. Supplementation of phosphate effectively increased the ratio of reduced to oxidized ascorbate and glutathione, contributing to the alleviation of arsenic toxicity.