A FUNGAL TOXIN ELICIT NITRIC OXIDE SIGNAL MEDIATED INNATE IMMUNE RESPONSE IN Rauvolfia

The present study demonstrate correlation of elicitor like activity of Alternaria alternata toxin with the increased production of nitric oxide (NO) in Rauvolfia serpentina which might serve as an essential signal molecule for triggering phenols, defense enzymes including peroxidase (PO), polyphenoloxidase (PPO), phenylalanine ammonia lyase (PAL) and pathogenesis-related protein (PR) such as ß-1, 3 glucanase accumulation. Here in vitro regenerated plants of R. serpentina grown under green house condition when treated with optimized concentration of toxin (50 mgL-1) showed an increased accumulation of phenols, PO, PPO, PAL and ß-1, 3 glucanase. Simultaneously, a raise in NO was also observed in the foliar tissues treated with toxin. This was further confirmed by using a fluorescent probe, 4, 5-diaminofluorescein diacetate (DAF-2DA). Parallely, to investigate the possible involvement of nitric oxide in toxin induced defense response in planta, R. serpentina plants were treated with NO synthase inhibitor, NG -nitro-L-arginine-methyl ester (L-NAME) at 10 μM and NO scavenger, 2-(4- carboxyphenyl)- 4,4,5,5- tetramethylimidazoline-1-oxyl-3-oxide (cPTIO) at 100 μM showed a decline in all the defense enzymes, PR proteins and total phenols. In contrast, application of 100 μM of sodium nitroprusside (SNP), a NO donor had reversed the inhibitory effect of the NOS inhibitor and NO scavenger.