Inter-species variation of malate sensitivity of PEP carboxylase in CAM plants and the mechanism of the regulation

以13种CAM为材料，研究了磷酸烯醇式丙酮酸羧化酶（PEPC）的最适pH值及其对苹果酸敏感性的种间差异。特别是香荚兰表现出两种PEPC的最适pH值，这说明香荚兰中存在PEPC同工酶。PEPC对苹果酸的敏感性也存在种间差异。香根草属羽叶型，其苹果酸敏感性昼夜变化明显。草原景天属于凤梨类植物，不表现昼夜变化。以PEPC对苹果酸敏感性不同的3种CAM植物-- PEPC在三种CAM植物叶肉细胞中的定位不同。在羽叶锦鸡儿中，PEPC主要分布在细胞质和生物膜中。在丛毛蒿中，PEPC主要分布在细胞质和生物膜表面。大叶黄杨的PEPC大部分存在于生物膜中，占80%以上。结果表明，不同CAM对苹果酸敏感性的差异与PEPC在细胞内的位置有关，而魔芋、羽叶魔芋和大果魔芋的等电点分别为5.1 ~ 5.2和5.8 ~ 5.9。

Using 13 CAM species, optimum pH of phosphoenolpyruvate carboxylase(PEPC)and inter-species variation of malate sensitivities of PEPC were studied ; Optimum pH of PEPC showed significant intre-species difference among species. Especially Vanilla fragrant showed two optimum pHs of PEPC.This suggested the isozyme of PEPC in V.fragrant. Malate sensitivity of PEPC also showed difference in species. V.fragrant was grouped into the type of pinnata, which showed clear day/night change of the malate sensitivity. Sedum praealtum was classified to the type of ananas, which did not show the day/night change. Phalaenopsis, Opuntia vulgaris, Dendrobium ekapol, Hoya carnosa, Crassula argentea, Aloe thraskii, Porturacaria afra were grouped into the type of daigremontiana, which showed intermediate of above types.Using three CAM plants, Anansu comosus, Kalanchoe daigremontiana, and K.pinnata, which showed different malate sensitivity of PEPC,located of PEPC in the cell and characteristics of isoelectric focusing were studied. The location of PEPC in the mesophyll cell was in different among three CAM plants. In K.pinnata, PEPC located mainly in cytosol and biomembrane. In A.comosus, PEPC distributed in the cytosol and on the surface of biomembrane. Most of PEPC of K.daigremontiana, more than 80%, existed in the biomembrane. Consequently, it was suggested that the difference of malate sensitivity in CAM species related to the inter-cellular location of PEPC.Isoelectric point of A.comosus, and K.pinnata and K.daigremonteana, was observed at 5.1 to 5.2, and 5.8 to 5.9, respectively.