Department of Plant Biology, Sapienza University of Rome, Piazzale Aldo Moro 5, 00185 Rome, Italy.
BMC Plant Biol. 2010 Apr 19;10:69. doi: 10.1186/1471-2229-10-69.
Camptotheca acuminata is a major natural source of the terpenoid indole alkaloid camptothecin (CPT). At present, little is known about the cellular distribution of the biosynthesis of CPT, which would be useful knowledge for developing new strategies and technologies for improving alkaloid production.
The pattern of CPT accumulation was compared with the expression pattern of some genes involved in CPT biosynthesis in C. acuminata [i.e., Ca-TDC1 and Ca-TDC2 (encoding for tryptophan decarboxylase) and Ca-HGO (encoding for 10-hydroxygeraniol oxidoreductase)]. Both CPT accumulation and gene expression were investigated in plants at different degrees of development and in plantlets subjected to drought-stress. In all organs, CPT accumulation was detected in epidermal idioblasts, in some glandular trichomes, and in groups of idioblast cells localized in parenchyma tissues. Drought-stress caused an increase in CPT accumulation and in the number of glandular trichomes containing CPT, whereas no increase in epidermal or parenchymatous idioblasts was observed. In the leaf, Ca-TDC1 expression was detected in some epidermal cells and in groups of mesophyll cells but not in glandular trichomes; in the stem, it was observed in parenchyma cells of the vascular tissue; in the root, no expression was detected. Ca-TDC2 expression was observed exclusively in leaves of plantlets subjected to drought-stress, in the same sites described for Ca-TDC1. In the leaf, Ca-HGO was detected in all chlorenchyma cells; in the stem, it was observed in the same sites described for Ca-TDC1; in the root, no expression was detected.
The finding that the sites of CPT accumulation are not consistently the same as those in which the studied genes are expressed demonstrates an organ-to-organ and cell-to-cell translocation of CPT or its precursors.
喜树是萜吲哚生物碱喜树碱（CPT）的主要天然来源。目前，关于 CPT 生物合成的细胞分布知之甚少，这对于开发提高生物碱产量的新策略和技术将是有用的知识。
比较了喜树中 CPT 积累的模式与参与 CPT 生物合成的一些基因（即 Ca-TDC1 和 Ca-TDC2（编码色氨酸脱羧酶）和 Ca-HGO（编码 10-羟基香叶醇氧化还原酶））的表达模式。在不同发育程度的植物和干旱胁迫下的植物中都研究了 CPT 积累和基因表达。在所有器官中，CPT 积累都在表皮异形细胞、一些腺毛和位于薄壁组织中的异形细胞群中检测到。干旱胁迫导致 CPT 积累和含有 CPT 的腺毛数量增加，而表皮或薄壁组织异形细胞没有增加。在叶片中，Ca-TDC1 表达在一些表皮细胞和叶肉细胞群中，但不在腺毛中；在茎中，它存在于维管束的薄壁细胞中；在根中，没有检测到表达。Ca-TDC2 的表达仅在干旱胁迫下的植物叶片中观察到，与 Ca-TDC1 描述的部位相同。在叶片中，Ca-HGO 存在于所有叶绿体细胞中；在茎中，与 Ca-TDC1 描述的部位相同；在根中，没有检测到表达。
CPT 积累的部位与研究基因表达的部位不一致的发现表明 CPT 或其前体在器官间和细胞间发生了转移。
