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Arsenic toxicity is the most commonly experienced challenge of rice plants due to irrigation with arsenic-polluted groundwater and their cultivation in water logging environment which poses threat to human health, particularly in Bangladesh and West Bengal (India). In the present study, hydroponically grown eight rice cultivars, viz., Bhutmuri, Kumargore, Binni, Vijaya, Tulsibhog, Badshabhog, Pusa basmati, and Swarnadhan, were screened for arsenic tolerance by using physiological and molecular parameters. Treatment with 25 μM, 50 μM, and 75 μM arsenate resulted in dosage-based retardation in growth and water content in all the tested cultivars due to accumulation of total arsenic along with the enhanced activity of arsenate reductase with more severe effects exhibited in cvs. Swarnadhan, Pusa basmati, Badshabhog, and Tulsibhog. Arsenic sensitivity of rice cultivars was evaluated in terms of oxidative stress markers generation, antioxidant enzyme activities, and level of genotoxicity. Under arsenate-challenged conditions, the levels of oxidative stress markers, viz., HO, MDA, and proline, and activities of antioxidant enzymes, viz., SOD and CAT, along with the level of genotoxicity analyzed by RAPD profiling were altered in variable levels in all tested rice cultivars and showed a significant alteration in band patterns in arsenate-treated seedlings of cvs. Swarnadhan, Pusa basmati, Badshabhog, and Tulsibhog in terms of appearance of new bands and disappearance of normal bands that were presented in untreated seedlings led to reduction in genomic template stability due to their high susceptibility to arsenic toxicity. Cultivar- and dose-dependent alteration of parameters tested including the rate of As accumulation showed that cvs. Kumargore, Binni, and Vijaya, specially Bhutmuri, were characterized as arsenate tolerant and could be cultivated in arsenic-prone areas to minimize level of toxicity and potential health hazards.

Arsenic contamination of groundwater is a major concern for its use as drinking water and crop irrigation in many regions of the world. Arsenic is absorbed by rice plants from arsenic contaminated water during irrigation, hampers growth and agricultural productivity. The aim of the study was to mitigate the activity of TCA cycle, synthesis of γ-aminobutyric acid (GABA) and polyamines (PAs) in rice (Oryza sativa L. cv. MTU-1010) seedlings under arsenate (As-V) stress [25 µM, 50 µM and 75 µM] by silicon (Si) [2 mM] and selenium (Se) [5 µM] amendments, and to investigate which chemical was more potential to combat this threat. As(V) application decreased the activities of tested respiratory enzymes while the levels of organic acids (OAs) were increased in the test seedlings. Co-application of Si and As(V) increased the activities of respiratory enzymes, consequently further increased accumulation of OAs that were more than Se with As(V) application in the test seedlings. GABA accumulation along with the activities of its regulatory enzymes were enhanced under As(V) stress. During joint application of Si and As(V) and Se and As(V) said parameters were decreased showing defensive role of these chemicals to resist As(V) toxicity in rice but amendment of Si was more potential than Se amendment resulted reduction of stress induced damage in the test seedlings. PAs trigger tolerance mechanism against stress in plants. PAs viz., Putrescine, spermidine and spermine were synthesized more during Si and Se amendments in As(V) contaminated rice seedlings to combat the effect of stress. Si amendment substantially modulated the toxic effects caused by As(V) over Se amendment in As(V) challenged test seedlings. Thus in future application Si enriched fertilizer will be bene cial than application of Se enriched fertilizer to grow rice plants with normal vigor in arsenic contaminated soil.

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