Voznesenskaya Elena V, Chuong Simon D X, Koteyeva Nuria K, Edwards Gerald E, Franceschi Vincent R
Laboratory of Anatomy and Morphology, VL Komarov Botanical Institute of Russian Academy of Sciences, Prof Popov Street 2, 197376, St Petersburg, Russia.
School of Biological Sciences, Washington State University, Pullman, WA 99164-4236, USA.
Funct Plant Biol. 2005 Feb;32(1):67-77. doi: 10.1071/FP04118.
The genus Aristida (Poaceae), is composed of species that have Kranz anatomy and C photosynthesis. Kranz anatomy typically consists of two photosynthetic cell types: a layer of mesophyll cells where atmospheric CO is fixed into C acids, and an internal, chlorenchymatous vascular bundle sheath to which C acids are transferred and then decarboxylated to donate CO to the C cycle. The anatomy of Aristida species is unusual as it has three distinct layers of chlorenchyma cells surrounding the vascular tissue: an inner bundle sheath, an outer bundle sheath and the mesophyll cells. In this study of Aristida purpurea Nutt. var. longiseta, the functions of the three layers of chlorenchyma cells relative to the C photosynthetic mechanism were determined using ultrastructural analysis, western blots, immunolocalisation of photosynthetic enzymes and starch histochemistry. The results indicate that mesophyll cells contain high levels of phosphoenolpyruvate carboxylase (PEPC) and pyruvate Pi dikinase (PPDK), and function to capture CO in the C cycle. The inner bundle sheath, which is high in Rubisco and contains NADP-malic enzyme and glycine decarboxylase, functions to transfer CO to the C cycle through decarboxylation of C acids and by decarboxylation of glycine in the glycolate pathway. The outer chlorenchymatous sheath is where ADPG pyrophosphorylase is mainly located, and this cell layer functions as the primary site of starch storage. The outer sheath, which has low levels of Rubisco and PEPC, may also have a role in refixation of any CO that leaks from the inner bundle sheath cells.
三芒草属（禾本科）由具有花环解剖结构和C4光合作用的物种组成。花环解剖结构通常由两种光合细胞类型组成：一层叶肉细胞，大气中的CO2在其中固定为C4酸；以及内部的、含叶绿体的维管束鞘，C4酸被转移到该维管束鞘中，然后脱羧以将CO2提供给C3循环。三芒草属物种的解剖结构不同寻常，因为其维管组织周围有三层不同的薄壁细胞层：内层维管束鞘、外层维管束鞘和叶肉细胞。在这项对长芒三芒草（Aristida purpurea Nutt. var. longiseta）的研究中，利用超微结构分析、蛋白质免疫印迹、光合酶的免疫定位和淀粉组织化学确定了这三层薄壁细胞相对于C4光合机制的功能。结果表明，叶肉细胞含有高水平的磷酸烯醇式丙酮酸羧化酶（PEPC）和丙酮酸磷酸双激酶（PPDK），其功能是在C4循环中捕获CO2。内层维管束鞘中Rubisco含量高，含有NADP-苹果酸酶和甘氨酸脱羧酶，其功能是通过C4酸的脱羧以及通过乙醇酸途径中甘氨酸的脱羧将CO2转移到C3循环中。外层薄壁鞘是ADPG焦磷酸化酶的主要所在部位，该细胞层作为淀粉储存的主要位点发挥作用。外层鞘中Rubisco和PEPC水平较低，可能也在重新固定从内层维管束鞘细胞泄漏的任何CO2方面发挥作用。
