Langdale J A, Zelitch I, Miller E, Nelson T
Department of Biology, Yale University, New Haven, CT 06511.
EMBO J. 1988 Dec 1;7(12):3643-51. doi: 10.1002/j.1460-2075.1988.tb03245.x.
C4 plants such as maize partition photosynthetic activities in two morphologically distinct cell types, bundle sheath (BS) and mesophyll (M), which lie as concentric layers around veins. We show that both light and cell position relative to veins influence C4 photosynthetic gene expression. A pattern of gene expression characteristic of C3 plants [ribulose bisphosphate carboxylase (RuBPCase) and light-harvesting chlorophyll a/b binding protein in all photosynthetic cells] is observed in leaf-like organs such as husk leaves, which are sparsely vascularized. This pattern of gene expression reflects direct fixation of CO2 in the C3 photosynthetic pathway, as determined by O2 inhibition assays. Light induces a switch from C3-type to C4-type gene expression patterns in all leaves, primarily in cells that are close to a vein. We propose that light causes repression of RuBPCase expression in M cells, by a mechanism associated with the vascular system, and that this is an essential step in the induction of C4 photosynthesis.
诸如玉米之类的C4植物将光合作用活动分配到两种形态上不同的细胞类型中，即维管束鞘（BS）细胞和叶肉（M）细胞，它们围绕叶脉呈同心层排列。我们发现，光照以及细胞相对于叶脉的位置都会影响C4光合作用基因的表达。在诸如苞叶等维管束稀疏的叶状器官中，观察到了C3植物特有的基因表达模式[所有光合细胞中的核酮糖二磷酸羧化酶（RuBPCase）和捕光叶绿素a/b结合蛋白]。如通过氧气抑制试验所确定的，这种基因表达模式反映了在C3光合途径中二氧化碳的直接固定。光照会诱导所有叶片中从C3型基因表达模式向C4型基因表达模式的转变，主要发生在靠近叶脉的细胞中。我们提出，光照通过一种与维管系统相关的机制导致叶肉细胞中RuBPCase表达受到抑制，并且这是诱导C4光合作用的一个关键步骤。
