Plant Latex, from Ecological Interests to Bioactive Chemical Resources^[*]

Abstract

Historically, latex-bearing plants have been regarded as important medicinal resources in many countries due to their characteristic latex ingredients. They have also often been endowed with a social or cultural significance in religious or cult rituals or for hunting. Initial chemical studies focused on the protein or peptide content but recently the interest extended to smaller molecules. Latex has been found to contain a broad range of specialized metabolites such as terpenoids, cardenolides, alkaloids, and phenolics, which are partly responsible for their antibacterial, antifungal, anthelmintic, cytotoxic, and insect-repellent activities. The diversity in biology and chemistry of latexes is supposedly associated to their ecological roles in interactions with exogenous factors. Latexes contain unique compounds that are different to those found in their bearing plants. Exploring the feasibility of plant latex as a new type of bioactive chemical resource, this review paper covers the chemical characterization of plant latexes, extending this to various other plant exudates. Also, the factors influencing this chemical differentiation and the production, transportation, and chemistry of the latex exudates are described, based on ecological and biochemical mechanisms. We also proposed a latex coagulation model involving 4 general conserved steps. Therefore, the inherent defensive origin of latexes is recognized as their most valuable character and encourages one to pay attention to these materials as alternative sources to discover metabolites with insecticidal or antimicrobial activity.

Key words

plant exudates - latex coagulation - mechanical defense - bioactive latex metabolites - endophytes - interaction

^* Dedicated to Professor Dr. Cosimo Pizza 70th birthday in recognition of his outstanding contribution to natural product research.

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