The Role of Flavan-3-ols and Proanthocyanidins in Plant Defense

Flavanols occur as monomers or undergo structural complexing. They are intimately involved in the complex interactions between plants and their environment. In considerations of plant defense, major emphasis is laid on the large array of responses evolved by plants using the diversity of flavanols. Each process of defense is the result of a combination not only of biochemical aspects but also of anatomical mechanisms. Histological reactions, including the build-up of physical barriers, participate in the complex regulation of resistance. Even at the cellular level the amount and location of flavanols might determine resistance or susceptibiliy of the host. Some of these aspects have been discussed with special reference to host-pathogen interactions and fruit trees exposed to long periods of abiotic and biotic stresses.