Hydrogen Sulfide (H2S) Mitigates Arsenic (As)-Induced Toxicity in Pea (Pisum sativum L.) Plants by Regulating Osmoregulation, Antioxidant Defense System, Ascorbate Glutathione Cycle and Glyoxalase System

Arsenic (As) being a toxic metalloid adversely affects plant growth and yield, as well as poses severe risks to human health. Hydrogen sulfide (H2S) has emerged a vital signaling molecule regulating key plant growth processes under stress conditions. However, till date little information is available regarding the role of H2S in mitigating As toxicity in pea plants. In the present study, the effect of externally applied H2S and its scavenger hypotaurine (HT) on various morphological, physiological and biochemical parameters of pea plants was evaluated. Our results showed significant decline in root length (RL), shoot length (SL), dry biomass, photosynthetic parameters such as pigment content and gas exchange characteristics in pea plants subjected to As stress. However, H2S supplementation significantly decreased As accumulation in the roots and shoot, as well as considerably enhanced growth and photosynthetic parameters. Hydrogen peroxide (H2O2), malondialdehyde (MDA) and electrolyte leakage (EL) increased significantly in the As-treated plants, while H2S supplementation considerably reduced the levels of H2O2 and MDA as well as EL. Arsenic stress accelerated the activities of antioxidant and AsA-GSH cycle enzymes except that of CAT; however, the activities of these enzymes were found to be further increased by H2S supply including that of CAT. Furthermore, ascorbate (AsA), glutathione (GSH) and methylglyoxal (MG) levels were significantly enhanced by As stress, and were further intensified in the H2S-supplemented plants. Our results demonstrated significant role of H2S in reducing As accumulation and inducing upregulation of the AsA-GSH cycle to overcome ROS-mediated oxidative damage to the cellular components of pea plants. Hence, H2S reduced oxidative damage and promoted growth of pea plants under As stress, suggesting an important role of H2S in plant priming.