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Trichomes in plant defense
Trichomes not only benefit the plant physically, but also chemically. Trichomes can develop in a variety of forms including, hairs or as pocket-like structures called glandular trichomes. These glandular trichomes store species-specific secondary metabolites such as terpenoids and phenolics in a pocket like structure between the cell wall and the cuticle of the plant. When glandular trichomes burst upon contact, they release these secondary metabolites and the strong odor and bitter taste of these substances cause insect herbivores to repel. An example of trichomes used as a chemical defense against herbivores are found in the leaves of Urtica dioica. These leaves contain needle-like trichomes filled with a mix of histamine, oxalic acid, tartaric acid, formic acid, and serotonin which cause severe inflammation and irritation. These trichomes have a glassy looking tip which snaps off when it comes to contact with an herbivore and the needle-like trichome acts as a syringe, injecting the cocktail of histamines and acids into the skin.

Studies have shown that trichome morphology and chemical composition has a role in herbivory response. The response of insect Helicoverpa sea on tomato plants Rutgers and Alisa Craig as well as their respective mutants was monitored in a study conducted by Donglan and his colleagues. They found a higher insect resistance on Alisa Craig, its mutant, and Rutger tomato plants treated with methyl jasmonate, a jasminate rich chemical which induces trichrome growth. There was low insect resistance on Rutger mutants which were also treated with methyl jasmonate. An adjacent study tested the trichome morphology of these four tomato plants and it was determined that Alisa Craig, its mutant and Rutger wild type tomato plants are rich in glandular trichomes while Rutger mutants are rich in non-glandular trichomes. Overall, this study suggests that glandular trichome density is an important factor of insect resistance.