The defensive role of latex in plants: detrimental effects on insects (original) (raw)

2010, Arthropod-plant Interactions

The defensive role of the latex of Calotropis procera has recently been reported. In this study, latex proteins involved in detrimental effects on insects were evaluated on another important crop pest. The latex was fractionated to obtain its major protein fraction, which was then used to evaluate its insecticidal properties against Callosobruchus maculatus (Coleoptera: Bruchidae) in artificial bioassays. Laticifer proteins (LP) were investigated to characterize their action in such an activity. LP was highly insecticidal at doses as low as 0.1% (W/W). This effect was slightly augmented in F1 generation reared in artificial seeds containing LP at similar proportions of F0, but was fully reversed when F1 developed in LP-free seeds. The insecticidal proteins were not retained in a chitin column, and did not lose their insecticidal activity, even after heat treatment or pronase digestion. However, these samples inhibited papain (EC 3.4.22.2) activity and gut proteases of C. maculatus larvae, and a reverse zymogram showed the presence of protein bands resistant to papain digestion. These activities were not observed in unheated LP as they were probably masked by abundant endogenous cysteine protease (EC 3.4.22.16) activity present in unheated LP. LP was resistant to proteolysis when assayed with C. maculatus gut extract. However, gut proteins of C. maculatus were digested when incubated with LP. These observations and the deleterious effects of LP upon C. maculatus, reinforce the hypothesis that laticifer fluids are involved in plant defense against insects and indicate C. procera latex to be a source of promising insecticidal proteins. The inhibitor of proteolysis present in the latex seems to be resistant to heat and proteolysis and is certainly involved in the detrimental effects observed.

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