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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The Responses Of Plants To Environmental Stresses

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, α-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 are used by the pathogen in the infection process.

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Induced plant defences are those defences which are initiated after a pathogen infection has been detected. These defences are chemical changes within the cell wall which cause the formation of papillae, which in fungal attack form reinforced areas around the penetration peg, preventing the full insertion of the peg, Buchanan et al. (2000). The papillae are formed from callose and lignin. The lignification of the cell wall and callose deposition in the plasmodesmata give improved physical strength to prevent pathogen penetration, prevent pathogenic toxin diffusion and also prevent solute leakage from the plant cells, therefore starving the pathogens of ...

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This has the potential to be a really strong piece of work. There's some nice detail involved, and the student has thought of three strong areas to cover. To improve it he needs to - Write a clearer introduction, introducing the topic and explaining why stress is important. - Develop a cohesive plan for how the three types of stress will fit together. - Be consistent in how much detail he includes. - Include more biological examples, and citations to back up the work.