Latex: A Model for Understanding Mechanisms, Ecology, and Evolution of Plant Defense Against Herbivory

Latex is a sticky emulsion that exudes upon damage from specialized canals in about 10% of flowering plant species. Latex has no known primary metabolic function and has been strongly implicated in defense against herbivorous insects. Here we review historical hypotheses about the function of latex, evidence that it serves as a potent defense, and the chemistry and mode of action of the major constituent defense chemicals and proteins across a diversity of plant species. We further attempt to synthesize the characteristics of latex as a coordinated plant defense system. Herbivores that feed on latex-bearing plants typically evade contact with latex by severing the laticifers or feeding intercellularly, or may possess physiological adaptations. Convergent evolution appears to be rampant both in plants with latex and insects that exploit latex-bearing plants. Because latex shows phenotypic plasticity, heritability, and macoevolutionary lability, it is an ideal system to study plant-herbivore interactions using evolutionary approaches.