Impact of Cadmium Stress on Lowland Rice Plant and Scope of Hazards

Local lowland rice varieties are susceptible to cadmium stress. To address the impact of such stress, surface sterilized germinated lowland rice seedlings (Oryza sativa cv. Hazardus) were maintained in pots with autoclaved sand having Hoagland's solution in controls and 10 μM CdCl₂ solution (a moderate concentration) only in treated pots for 21 days in the laboratory net house of Calcutta University for the purpose of observing impact of exposure during October and December, 2013. Physiological parameters like biomass and length of ischolar_main and shoot are found to be decreased significantly in the treated plants. Cd-induced activation of antioxidant enzymes (ascorbate peroxidase, APX), increase of lipid peroxidation (malonaldehyde level, MDA) and increase in biosynthesis of free proline take place in the process. Phytochelatin synthase (PCS) plays a vital role in intracellular sequestration and compartmentation of divalent cations, e.g., Cd²⁺ within the vacuoles, as assessed by PCR, showing amplification in the shoot sample, in contrast to that in ischolar_main, which is a transcript expression. The active uptake of Cd²⁺ by the ischolar_main was found by overexpression of divalent cation transporter gene, OsNramp³. Reduced Rubisco gene expression and chlorophyll pigments showed that Cd²⁺ is actively translocated from ischolar_main to shoot, leaves and in the grains. This local cultivar of West Bengal is a highly susceptible variety resulting in the accumulation of Cd in its grain making it unsuitable for direct human consumption or as feed for cattle.