Latex proteins and enzymes involved in terpenoid biosynthesis of selected Euphorbia species: Euphorbia kansui Liou and Euphorbia helioscopia L.

Abstract

Abstract Euphorbia is the largest genus in Euphorbiaceae. The most species have non-articulated laticifers. During the development of non-articulated laticifers, some cytoplasm parts degenerate and lots of latex particles are synthesized and accumulated in the central vacuole. Latex proteins play significant roles in the laticifer development and latex particle synthesis. Therefore, latex proteomics of selected Euphorbia species: Euphorbia kansui Liou and Euphorbia helioscopia L. were introduced, especially latex proteins involved in laticifer development and terpenoid biosynthesis. Immunoblot and immunocytochemistry analyses on cysteine protease, clathrin heavy chain and AP-2 complex subunit beta-1 belonging to lysosome pathway showed that they were mainly distributed in vesicles derived from dicytosomes, which are called lysosome-like vesicles, and ubiquitin belonging to the proteasome pathway was widely distributed in the cytosol. As a result, it was speculated that lysosome pathway and proteasome pathway might be involved in the degradation of organelles and some cytoplasmic matrix in E. helioscopia laticifers. In addition, acetyl-CoA acetyltransferase, hydroxymethylglutaryl-CoA synthase, hydroxymethylglutaryl-CoA reductase, hydroxymethylglutaryl-CoA lyase, mevalonate disphosphate decarboxylase, isopentenyl diphosphate isomerase and farnesyl pyrophosphate synthase in terpenoid biosynthesis were detected in latex of Euphorbia plants. Immunocytochemistry analyses showed that acetyl-CoA acetyltransferase and mevalonate disphosphate decarboxylase were located in cisternae of endoplasmic reticulum, small vacuoles from endoplasmic reticulum and also distributed randomly in protoplasm of laticifer cells. Consequently, the isopentenyl pyrophosphate were speculated to be synthesized in the endoplasmic reticulum, and then transported to parts which dilated into small vacuoles, and the terpenoid was further synthesized into latex particles in these small vacuoles in E. helioscopia laticifers.