Abiotic stress induced over-expression of superoxide dismutase enzyme in transgenic Hevea brasiliensis

Abiotic stress induced over-expression of superoxide dismutase (SOD), catalase and eroxidase enzymes were studied in the transgenic embryogenic calli of Hevea brasiliensis, clone RRII 105. Two month old calli were transformed using Agrobacterium tumefaciens harbouring the binary vector containing neomycin phosphotransferase (npt-II) for kanamycin resistance as the selectable marker gene, [bêta]-glucuronidase (GUS) as the reporter gene and the sequence coding for SOD enzyme under the control of 34S promoter. The transformed calli were proliferated in half strength Murashige & Skoog medium containing 2,4-D ( 0.1mg/l), BA.( 0.3mg/l) and KIN( 0.2 mg/l). SOD enzyme [EC1. 15.1.1] is a scavenger of free radical and is an antiageing enzyme. Over-expression of SOD, peroxidase and catalase enzymes in response to abiotic stresses like water, osmotic and different light regimes in transgenic embryogenic callus cultures was determined. Water stress was induced by the addition of different concentrations (0.2-1.0%) of phytagel and osmotic stress was induced using polyethylene glycol (PEG), mannitol and sorbitol (2-10%) in the culture medium. The activity of enzymes was estimated spectrophotometrically. Over-expression of SOD enzyme was 50% when 0.4% phytagel was added to the medium. 40% over-expression was obtained when the culture medium was supplemented with 4.0% PEG. This reveals that the free radical scavenging enzymes were overexpressed in transformed tissues when subjected to abiotic stress. Efforts are now being made to study the molecular mechanism of SOD gene expression in transgenic Hevea brasiliensis in response to abiotic stress under in vitro conditions. (Résumé d'auteur