Taxol is a cytotoxic agent against various types of cancers. The cytotoxic activities of Taxol can be extended to its synthesizing plant. Here, Taxol is shown to have special synthesis, storage and transport mechanisms that avoid the toxic effects on its source plant. The sites of Taxol biosynthesis, transport and storage were revealed by quantification of plant Taxol, its intermediate baccatin III, the polyphenol side chain precursor , gene expression analysis of the major Taxol biosynthetic genes and in situ immuno-labeling. Although the biosynthesis of Taxol was limited by the expression of its biosynthetic genes and the presence of baccatin III, its presence did not correlate to baccatin III accumulation, nor to the expression of biosynthetic genes. However, Taxol presence positively correlated to polyphenol accumulation (late stage in Taxol assembly) and the resin-like hydrophobic bodies (HB, storage organelles). These results indicate that the presence of Taxol requires two complementary steps, biosynthesis followed by storage. Each step is limited by the availability of different precursors, which differ in their localization within the plant. Thus, the sites of biosynthesis, transport and storage of Taxol are different. Taxus media (Rehder) plant wood showed high concentrations of baccatin III and the expression of biosynthetic genes. However, the concentrations of Taxol, polyphenol and HB were very high in the plant outer layers including phloem and dead bark (rhytidome). Furthermore, in situ immuno-labeling showed that taxadiene synthase (the rate-limiting enzyme in Taxol biosynthesis) was mainly found in the wood, while Taxol primarily localized to the outer tissues. Conclusively, wood can be considered as the site of Taxol biosynthesis. Our data also propose that Taxol then accumulates into HB in order to permit its transport within the living plant tissues without causing toxic effects. This is followed by Taxol storage in the outer tissues including phloem and dead bark.

中文翻译：

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红豆杉培养基（Rehder）植物中紫杉醇的生物合成和储存场所：积累机制

紫杉醇是一种抗多种癌症的细胞毒剂。紫杉醇的细胞毒活性可以扩展到其合成植物。在这里，紫杉醇被证明具有特殊的合成、储存和运输机制，可以避免对其来源植物的毒性影响。通过植物紫杉醇、其中间体浆果赤霉素 III、多酚侧链前体的定量、主要紫杉醇生物合成基因的基因表达分析和原位免疫标记，揭示了紫杉醇生物合成、运输和储存的位点。尽管紫杉醇的生物合成受到其生物合成基因的表达和浆果赤霉素 III 的存在的限制，但其存在与浆果赤霉素 III 的积累无关，也与生物合成基因的表达无关。然而，紫杉醇的存在与多酚积累（紫杉醇组装的后期）和树脂样疏水体（HB，储存细胞器）呈正相关。这些结果表明紫杉醇的存在需要两个互补的步骤，生物合成和储存。每个步骤都受到不同前体的可用性的限制，这些前体在工厂内的定位不同。因此，紫杉醇的生物合成、运输和储存场所是不同的。红豆杉培养基 (Rehder) 植物木材显示出高浓度的浆果赤霉素 III 和生物合成基因的表达。然而，紫杉醇、多酚和 HB 在包括韧皮部和死树皮 (rhytidome) 在内的植物外层中的浓度非常高。此外，原位免疫标记显示紫杉二烯合酶（紫杉醇生物合成中的限速酶）主要存在于木材中，而紫杉醇主要定位于外部组织。最后，木材可以被认为是紫杉醇生物合成的场所。我们的数据还表明，紫杉醇随后会积累到 HB 中，以允许其在活植物组织内运输而不引起毒性作用。其次是紫杉醇储存在外部组织中，包括韧皮部和死树皮。