Laticifers, Latex, and Their Role in Plant Defense.

Latex, a sap produced by cells called laticifers, occurs in plants of wide taxonomic diversity. Plants exude latex sap in response to physical damage. Questions about the function of latex or the underlying mechanisms persist, but a role in defense is likely. The presence of constitutive peptidases in latex sap in addition to inducible and de novo synthesized pathogenesis-related proteins (PR-proteins), raises the question about the role that each sap component plays to protect plants and how synergism occurs among sap proteins in the course of herbivory or infection. Here we discuss a variety of functions for laticifer and latex in plant defense. We propose that latex peptidases build the front line of defense against herbivores or pathogens. Laticifers are highly specialized cells forming a tube-like network structure throughout the plant body, occurring in phylogenetically unrelated groups. Laticifers produce and store latex that is released upon rupture of laticifers. Compounds preformed in the latex, such as peptidases, chitinases, and chitin-binding proteins, play important defensive roles against microbes and/or insects. Latex peptidases emerge as defensive molecules in several ways. Synergism and cooperative work involving chemically diversified latex compounds permits the plant to defend against natural enemies. [ABSTRACT FROM AUTHOR]