Involvement of Protein Kinases in Induction of Acidic Isopolyphenol Oxidases in Cell Walls of Tomato by Fruit Extracts of Azadirachta indica A. Juss

Polyphenoloxidases have a defensive role against biotic stress. Neem fruit extract induces signaling pathway leading to defense response. The inhibitors of tyrosine protein kinases (Lavendustin A), protein serine/threonine kinases (Staurosporine), and protein kinase (K-252a) were utilized to study the role of protein kinase, as components of signaling leading to systemic acquired resistance by neem fruit extract in tomato plants. K252a-sensitive protein phosphorylation is involved in induction of signal transduction leading to appearance of a novel acidic isopolyphenoloxidases (Rf 0.71) ionically bound to cell walls of tomato plants treated with neem fruit extract. Physical pathogen barrier could be generated as a result of cross-linking of oxidized phenolics as well as due to oxidative cross-linking of cell wall proteins and enhanced lignin formation due to enhanced PPO activity. The cell wall bound acidic isopolyphenoloxidases which have a net positive charge may immobilize pathogens by interacting ionically with the negatively charged surfaces of plant pathogens.