Production of substances interfering with virus proliferation

In some cases plants are known to synthesise chemicals that inhibit crucial functions of pathogens. This makes plants immune to infection by respective pathogens. Let us consider what happens when cowpea mosaic virus infects a plant. Certain cultivars of cowpea produce a strong inhibitor of a viral proteinase activity. This proteinase is required to complete the life cycle of the virus as seen in the extracts of the protoplasts of these plants. These cultivars behave as immune against cowpea mosaic virus.

Resistance of many plants to viruses is a passive preformed type e.g., mechanical barriers, lack of compatible infection sites or metabolites required for virus replication. Yet a definite part of resistance is due to active plant response. This includes new synthesis of barriers against infection and spread of virus, and also of new substances interfering with virus replication.