Rapid response of rice plants to arsenite toxicity

Absorption of arsenic (As) by plant root is an essential activity that bridges the soil As concentration and physiological responses which can be monitored soon after exposure to As. In the present study, physiological responses to short exposure to arsenite (AsIII) was compared in two indigenous rice cultivars one adapted to temperate and humid (TH) and the second one to warm and humid (WH) climates.  Twenty days old plants were exposed to 75 µM AsIII, 6h. Expression of certain transporters, antioxidant system, and As detoxifying proteins were noticeable.  The levels of aquaporin transcripts OsNIP 2;1 (Lsi1), OsPIP1;3, and OsPIP2;6 significantly decreased in both cultivars. A more prominent reduction of aquaporin transcripts was observed in the WH cultivar and was accompanied by a lower AsIII uptake as compared to TH. The activity of superoxide dismutase, catalase, ascorbate peroxidase, and glutathione reductase enhanced in both cultivars, indicating the attempts to protect plants against AsIII-induced oxidative damage. These antioxidant responses were more pronounced in the WH cultivar and were accompanied by remarkably enhanced levels of reduced glutathione (a non-protein thiol) and phytochelatin, particularly in shoots. Although both cultivars responsed to AsIII very rapidly, based on the data presented here, it is likely that long-term adaptation of WH cultivar to warm and humid climate has driven genomic changes resulting in AsIII sequestration and other protective strategies against AsIII toxicity.