Arsenic (As) Inhibits Radicle Emergence and Elongation in Phaseolus aureus by Altering Starch-Metabolizing Enzymes Vis-A -Vis Disruption of Oxidative Metabolism

The present study investigated the effect of Arsenic (As; 5, 10, 50 mu M) on protein and sugar metabolism vis-A -vis oxidative damage during early germination process and radicle emergence (at 12, 24 and 48 h stage) in Phaseolus aureus. As-exposure (50 mu M) significantly enhanced protein content (by 40-60%), whereas carbohydrate content declined (by 31-44%) over that in the control. It was associated with a decline in the activities of proteases (47-53%), and increase in the activities of alpha- and beta-amylases, starch phosphorylases, and acid invertases by 3.0, 2.6, 4.8, and 1.7 times after 48 h exposure to 50 mu M As. The alteration in protein and carbohydrate metabolic machinery was also accompanied by As-induced reactive oxygen species (ROS)-mediated oxidative damage. As treatment enhanced malondialdehyde and hydrogen peroxide content by 46-252% and 23-216%, and hydroxyl and superoxide ion generation by 15-104% and 17-278%, respectively. As-induced lipid peroxidation and membrane disruption was confirmed by enhanced electrolyte leakage (by 49%) and reduced cell viability (by 43%). Furthermore, in response to 50 mu M As, the activities of superoxide dismutases, catalases, ascorbate peroxidases, guaiacol peroxidases, and glutathione reductases increased by 77%, 70%, 116%, 43% and 120%, respectively, in radicles at 48 h stage over that in the control. The study concludes that As inhibits radicle emergence and elongation in germinating P. aureus seeds by altering biochemical processes related to sugar metabolism and inducing an ROS-mediated oxidative damage.