Plant disease control is mainly based on the use of fungicides, bactericides, and insecticides-chemical compounds toxic to plant invaders, causative agents, or vectors of plant diseases. However, the detrimental effect of these chemicals or their degradation products on the environment and human health strongly imposes the search for novel, harmless means of disease control. Therefore, it is essential to introduce environmentally-friendly alternative measures for management of plant diseases. Induced plant resistance is one of the promising non-chemical strategies for the effective management of diseases. The host plant mediated resistance is governed by defense response genes encoding for production of various pathogenesis-related (PR) proteins. This review chiefly explains the biochemical response of plant defense mechanism pertaining to defense-related enzymes which have been identified as PR proteins.