Drought conditions, low and high temperatures, increased salt levels, pathogens and insects are common environmental stresses which plants are exposed to. Over time, plants have evolved unique mechanisms to respond to the stresses

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Drought conditions, low and high temperatures, increased salt levels, pathogens and insects are common environmental stresses which plants are exposed to. Over time, plants have evolved unique mechanisms to respond to the stresses imposed in them.

In response to pathogen infection, plants have two types of defence; constitutive and induced responses.

Constitutive defences are those which are passive and always present in the plant. These defences are those such as the cuticle which is composed of waxes, cutin and pectin and the cell wall, composed of cellulose, pectin and lignin, both of which act as structural barriers against pathogens. There are preformed pathogen inhibitors such as saponins which disrupts pathogen cell membranes. For example, ?-tomatine in tomatoes acts against many fungal species. Other preformed inhibitors include alkaloids, phenols and tannins. Defence proteins are also present; lectins bind sugar groups such as chitin, which in fungal species binds to chitin in fungal walls and slows sungal growth. RIPs or ribosome inactivating proteins disrups viral replication by deactivating the plants ribosomes, therefore preventing cell replication and therefore also the viral pathogens replication. Hydrolases are present which break down the components of the pathogens and enzyme inhibitors inhibit enzymes which