Effect of Arsenic Toxicity on Photosynthesis, Oxidative Stress and Alleviation of Toxicitywith Herbal Extracts in Growing Rice Seedlings

When seedlings of an Indica rice cultivar Malaviya-36 were raised for 8 days in hydroponics in Yoshida nutrient solution containing 25 ìM NaAsO₂, it was observed that arsenic treatment to the seedlings caused decline in plant height, fresh weight, relative water content, net photosynthetic rate, stomatal conductance, intracellular CO₂ concentration and transpiration rate. The decline was greater with increase in the duration of As treatment. Arsenic treated seedlings showed elevated levels of the reactive oxygen species superoxide radicals, H₂O₂ and increased oxidative stress in the tissues. When aqueous extracts prepared from leaves of the two plants, Neem (Azadirachta indica) and Tulsi (Ocimum sanctum) were added in As containing growth medium, a marked alleviation of As toxicity was observed in relation to growth parameters, photosynthetic activities and extent of oxidative stress in the tissues. Results suggest that both A. indica and O. sanctum aqueous extracts have potential to alleviate arsenic toxicity in rice seedlings with A. indica extract showing greater efficacy than O. sanctum.