SUMMARYRecalcitrant seeds of Shorea robusta (sal) exhibit 100"o viability up to 4 d after maturity. The rapid loss of viability after 4 d is associated with the reduction in moisture content below the lowest safe moisture content (37%). Seed becomes non-viable on 8 d. Increased leakage of electrolytes in seeds and lipid peroxidation in embryonic axes was discernible immediately from 0 d. In embryonic axes, very low levels of superoxide ('O^') were maintained up to 4 d and a sharp increase was registered up to 7 d. It is suggested that loss of moisture content in sal seeds below 21°.(, (after 4 d) induces substantial leakage loss probably due to increased lipid peroxidation and 'O.f radical formation which are responsible for severe membrane perturbations leading to rapid loss of viability. In embryonic axes SOD activity was recorded only in IOCVQ viable seeds.

Arsenic (As) is one of the highly toxic metalloids distributed ubiquitously in nature. Two inorganic forms of As are present abundantly: arsenite (As

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The freshly harvested mature neem seeds (42.2 % seed moisture content) with 100 % viability deteriorate when naturally desiccated to below 10.9 %. The desiccation-induced loss of viability was closely associated with over accumulation of superoxide anion and lipid peroxidation products both in the embryonic axes and cotyledons. The levels of superoxide anion and lipid peroxidation products were higher in axes compared to cotyledons. Superoxide dismutase activity was not much affected, both in the axes and cotyledons of 100 % viable seeds during desiccation from 42.2 % to 10.9 % seed moisture content. Steep rise in its activity was observed during drying below lowest safe moisture content (LSMC). Activities of catalase and peroxidase exhibited substantially higher levels in the 100 % viable seeds dehydrated up to LSMC. Their activities declined sharply in seeds with water content below LSMC. Impairment of catalase and peroxidase activities possibly lead to enhanced accumulation of reactive oxygen species. The accumulation of superoxide anion, lipid peroxidation and differential expression of superoxide dismutase and catalse/peroxidse activities in response to desiccation (below LSMC) is discussed to explain the intermediate storage physiology of neem seeds.List of abbreviations: L S M C : least safe moisture content; M D A : malondialdehyde; ROS : reactive oxygen species; SOD : superoxide dismutase;