School of Biochemistry, D. A. University, Khandwa Road, Indore-452 001
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The supply of sodium arsenate in the presence of nitrate to excised bean leaf segments caused a reduction in in vivo nitrate reductase activity (NRA), endogenous nitrate pool, chlorophyll content and peroxidase activity. In the time course study, the inhibitory effect of As on in vivo NRA persisted through out from 2h to 16h. The toxic effect of As was increased by the inclusion of inhibitors, such as, cycloheximide, chloramphenicol, lincomycin and sodium tungstate, amongst which cycloheximide was most effective and lincomycin the least. Cystein, reduced glutathion (GSH) and sucrose were highly effective in preventing inhibition of activities of NAR and cytochrome reductace by As. Molybdic acid was effective against inhibition of in vitro NRA and cytochromec reductase but not of in vivo NRA. The experiments demonstrate that arsenate exhibits an inhibitory effect on NR in bean leaf segments, which involves reduced synthesis of the enzyme and also an effect on activity of enzyme possibly through thiol modulation.
