Detection of three wound-induced proteins in papaya latex

The effects of routine mechanical wounding for latex collection from unripe fruits of the tropical Carica papaya tree were investigated. For that purpose, the protein composition of three different latexes was analyzed. The first one, commercially available, was provided in the form of a spray-dried powder, the second one was harvested from fully grown but unripe papaya fruits that are regularly tapped for latex production and the last one, was obtained from similar fruits wounded for the first time. Repeated mechanical wounding was found to profoundly affect the protein content of the latex inducing, among others, activation of papain. Regularly tapped latexes also accumulated several low molecular weight proteins not yet identified, as well as three proteins identified as a trypsin inhibitor, a class-II chitinase and a glutaminyl cyclase on the basis of their enzymatic or inhibitory activities and chromatographic elution profiles. This latter was found here, for the first time, to be a wound-induced protein. The roles of these proteins in the plant defense mechanism are discussed.