Boinski J J, Wang J L, Xu P, Hotchkiss T, Berry J O
Department of Biological Sciences, State University of New York, Buffalo 14260.
Plant Mol Biol. 1993 Jun;22(3):397-410. doi: 10.1007/BF00015971.
Plants that utilize the highly efficient C4 photosynthetic pathway possess two types of specialized leaf cells, the mesophyll and bundle sheath. In mature leaves of amaranth, a dicotyledonous C4 plant, ribulose 1,5-bisphosphate carboxylase (Rubisco) is localized specifically to the chloroplasts of bundle sheath cells, and is not present in the chloroplasts of mesophyll cells. The cell type-specific expression of the chloroplast-encoded Rubisco large subunit (rbcL) gene, and other representative chloroplastic genes, was investigated by using separated bundle sheath and mesophyll chloroplasts prepared from mature amaranth leaves. One-dimensional SDS-polyacrylamide gel electrophoresis revealed several differences in the polypeptide compositions of the two chloroplast types. Western analysis demonstrated that, as in the intact leaves, the Rubisco LSU polypeptide was present only in chloroplast preparations from bundle sheath cells. Pyruvate orthophosphate dikinase (PPdK), a nuclear-encoded chloroplastic enzyme, was found only in the mesophyll chloroplast preparations. rbcL mRNA was present only in the bundle sheath chloroplast preparations, whereas transcripts for the chloroplast-encoded psbA, psaA-B, and rpl2 genes were present in both chloroplast types. Although the rbcL message accumulated only in bundle sheath chloroplasts, run-on transcription analysis indicated that the rbcL gene was transcribed in both bundle sheath and mesophyll chloroplast preparations. Therefore, differential rbcL gene expression in the isolated C4 chloroplasts is regulated, at least in part, at the post-transcriptional level. Possibly this control is mediated by differential processing or stabilization of the rbcL transcript.
利用高效C4光合途径的植物拥有两种特殊的叶细胞，即叶肉细胞和维管束鞘细胞。在双子叶C4植物苋菜的成熟叶片中，1,5-二磷酸核酮糖羧化酶（Rubisco）特异性地定位于维管束鞘细胞的叶绿体中，而不存在于叶肉细胞的叶绿体中。通过使用从苋菜成熟叶片中分离得到的维管束鞘和叶肉叶绿体，研究了叶绿体编码的Rubisco大亚基（rbcL）基因以及其他代表性叶绿体基因的细胞类型特异性表达。一维SDS-聚丙烯酰胺凝胶电泳揭示了两种叶绿体类型在多肽组成上的几个差异。Western分析表明，与完整叶片一样，Rubisco大亚基多肽仅存在于维管束鞘细胞的叶绿体提取物中。磷酸丙酮酸双激酶（PPdK）是一种核编码的叶绿体酶，仅在叶肉叶绿体提取物中发现。rbcL mRNA仅存在于维管束鞘叶绿体提取物中，而叶绿体编码的psbA、psaA-B和rpl2基因的转录本在两种叶绿体类型中均存在。尽管rbcL信息仅在维管束鞘叶绿体中积累，但连续转录分析表明rbcL基因在维管束鞘和叶肉叶绿体提取物中均有转录。因此，分离的C4叶绿体中rbcL基因的差异表达至少部分是在转录后水平上受到调控的。这种调控可能是由rbcL转录本的差异加工或稳定介导的。
