Xylanse-Induced Cell Death Events in Detached Tobacco Leaves

Abstract

ABSTRACTPlant-pathogen interactions are associated with plant defense mechanism known as hypersensitive response (HR), which is a form of programmed cell death (PCD). In the present work we have tested the potency of chemicals, proven as PCD inhibitors in other systems, to prevent the spread of cell death in detached tobacco leaves challenged with β- xylanase from Aspergillus awamori K1. Xylanase induced cell death that was accompanied by electrolyte leakage and increased levels of the stress metabolites hydrogen peroxide and malondialdehyde. Lesion development, ion leakage and the production of stress metabolites were suppressed if the infiltration site was pre-infiltrated with broad range caspase inhibitor benzyoxycarbonyl-Asp-2,6-dichlorobenzoyloxymethylketone (Z-Asp-CH2-DCB), cysteine protease inhibitor iodoacetamide (IA), serine protease inhibitor 4-(2-aminoethyl) benzenesulfonyl fluoride hydrochloride (AEBSF), the antioxidant l-galactone-γ-lactone (L-gal) and the ethylene blocker (S)-trans-2-Amino-4-(2-aminoethoxy)-3-butenoic acid hydrochloride (AVG). Massive ROS accumulation, as determined by staining with 3–3′-diaminobenzidine and 2′,7′-dichlorofluorescein diacetate, occurred in xylanase-infiltrated lesions and was substantially reduced by the inhibitors. To the best of our knowledge, this is the first report showing that β-xylanase produced by Aspergillus awamori K1 induces cell death response in tobacco and proteolysis, ROS and ethylene are involved in the mediation of the signaling.