Question

Name important defence mechanisms in plants against herbivory.

Answer 1

For plants, herbivores are the predators. Nearly 25 per cent of all insects are known to be phytophagous (feeding on plant sap and other parts of plants). The problem is severe for plants because, unlike animals, they cannot run away from their predators. Plants, therefore, have evolved an astonishing variety of morphological and chemical defences against herbivores. Thorns and spines (Acacia, cactus) are the most common morphological means of defence. Some plants release toxins that poison attacking herbivores, while others produce complex compounds that affect the attacker's growth cycle or ability to digest the plant. Plants have evolved several secondary metabolites used in plant defence, known as antiherbivory chemicals. These are nitrogen compounds (alkaloids, cyanogenic glycosides, benzoxazinoids), terpenoids, and phenolics. The weed Calotropis grows in abandoned fields. This plant produces highly poisonous cardiac glycosides. This is the reason why any cattle or goats are not commonly seen grazing on this plant.