The correct option for the given question is a. production of the unusual amino acid is canavanine , is a defense some plants use against herbivory.
A plant's first line of defense is the intact and impenetrable barrier of the bark and waxy cuticle. Both protect plants from predators. Other antiherbivore adaptations include hard shells, thorns (modified branches), and spines (modified leaves). Plant structural features such as leaf surface wax, spines or trichomes, cell wall thickness/and lignification form the first physical barriers to herbivore foraging and secondary amino acid metabolites such as toxins, It also affects growth, development and digestibility. Reducers are the next barrier. Plants evade herbivory by hiding, building structural barriers, producing and acquiring chemical toxins, and recruiting predatory "bodyguards."
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