BackgroundSaikosaponin-d (SSd) is an important active component of Bupleurum scorzonerifolium Willd., a traditional Chinese medicinal herb. Thus far, the biosynthetic pathway and biosynthetic site of saikosaponins in Bupleurum are largely unknown. The cellular localization of SSd will help in understanding saikosaponin biosynthesis and regulation.ResultsIn this study, we characterize for the first time the localization of SSd in B. scorzonerifolium tissues and cells using histochemistry and immunoelectron microscopy. The results show that the saikosaponin distribution in different plant organs changes as they mature. The number of SSd gold particles distinctly differed among the roots, stems, and leaves, with the particles mainly concentrated in the roots. The gold particles were mainly observed in vacuoles, with a few particles in the protoplasm; hence, SSd is mainly stored in vacuoles.ConclusionsWe speculate that saikosaponins are mainly synthesized via the mevalonate pathway in the protoplasm in young organs, and then transported to the central vacuole by the endoplasmic reticulum (ER) or the fusion of vacuoles, to protect plants from self-poisoning with the accumulation of more saikosaponins.Electronic supplementary materialThe online version of this article (doi:10.1186/1999-3110-54-32) contains supplementary material, which is available to authorized users.
At present, the lysosome pathway (LP) and proteasome pathway (PP) are known as major clearance systems in eukaryotic cells. The laticifer, a secretory tissue, degrades some cytoplasm during development. In this study, we investigated the distribution of LP and PP in non‐articulated laticifers of Euphorbia helioscopia L. Electron microscopy revealed that, plastids, mitochondria and some cyotsol were degraded in the late development laticifers, where there were numerous vesicles originated from dicytosomes. Accordingly, some key proteins in LP and PP were detected in E. helioscopia latex using isobaric tags for relative and absolute quantitation (iTRAQ) proteomics. Further immunohistochemistry analysis revealed that the clathrin heavy chain (CHC) belonging to LP and the ubiquitin‐mediated proteasome degradation increases gradually as the laticifer develops. Immuno‐electron microscopy revealed that the cysteine protease, CHC and AP‐2 complex subunit beta‐1 belonging to LP were mainly distributed in vesicles deriving from dicytosomes, which we called lysosome‐like vesicles. Ubiquitin was widely distributed in the cytosol, and proteasome activity was significantly reduced when various concentrations of the inhibitor MG132 were added to the latex total protein. We hypothesize that LP and PP are distributed in E. helioscopia laticifers; and it was speculated that LP and PP might be involved in the degradation of organelles and some cytoplasmic matrix in E. helioscopia laticifers.
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