Saponins versus plant fungal pathogens

The production of low-molecular-weight antimicrobial molecules within plants is one component of defense against pathogens. Among them, preformed antimicrobial compounds (phytoanticipins) are the first biochemical barriers against pathogens. Saponins (a group of phytoanticipins) are present constitutively in plants and play important roles in plant defense. A variety of biological roles have been postulated for different saponins, involving allelopathic activity, defense against insects and pathogens. The mechanism of antifungal action of saponins is not well understood but it is believed that they complex with sterols in the cell membrane, leading to pore formation and consequent loss of membrane integrity. Saponins that have been studied in detail in relation to their potential role in plant defense against attack by phytopathogenic fungi are triterpenoid avenacins in oat roots and the steroidal glycoalkaloids α-tomatine in the leaves of tomato. Here we present a review about the two saponins that have been proved to have antimicrobial activity and have a role in plant defense.