Potentiality to increase photo synthetic rate by introducing carbonic anhydrase cDNA into cropleaves

叶肉细胞对CO_2转运的抗性是C3光合成碳同化(PCA)的限制步骤之一。为了提高植物的来源能力，我们研究了在叶肉细胞质中导入外源碳酸酐酶(CA)活性对其PCA率的影响。研究结果如下：1)利用农杆菌叶盘法，将含有小鼠CA基因的基因盒导入烟草。外源CA基因在基因、蛋白质和活性水平上均有表达。2)在CO_2浓度为主要限制因子的条件下，即低CO_2或高O_2条件下，转基因植株的PCA率高于野生植株。3)利用改进的启动子获得了另一株高表达外源CA活性的转基因植株。我们观察到，这种植物不仅在较低的CO_2浓度下，而且在环境CO_2条件下，都表现出显着较高的主成分分析速率。4)叶绿素荧光分析表明，CA活性的引入降低了叶片对无机碳转移的抗性。5)在高光强条件下，外源CA活性的引入导致叶面积和干重的增加，固碳过程是PCA的限制因素。这些结果表明，在叶肉细胞质中导入外源CA活性可能通过降低叶肉对无机碳转移的阻力来提高PCA活性和生长速率，特别是在CO2限制条件下。

Mesophyll resistance in CO_2 transfer is one of the limiting steps in the C3 photoosynthetic carbon assimilation (PCA). Aiming at the improving the source ability of the plant, we examined the effects of the introduced foreign carbonic anhydrase (CA) activity in the mesophyll cytoplasm on its PCA rate. The obtained results are as follows ;1)With the Agrobacterium leaf disk method, the gene cassettes involving the mouse CA cDNA were introduced into the tobacco. The foreign CA gene was expressed at gene, protein and activity levels. 2)Under the conditions where the CO_2 concentration was the main limiting factor to C3 PCA,i.e. low CO_2 or high O_2 conditions, the transgenic plants showed higher PCA rate compared with the wild plant. 3)Another transgenic plants expressing higher level of foreign CA activity were produced by using an improved promoter. We observed that this plant showed significantly higher PCA rate not only under lower CO_2 concentrations but also under ambient CO_2 condition. 4)Chlorophyll fluorescence analysis showed that the mesophyll resistance for inorganic carbon transfer was reduced by the introduction of CA activity. 5)Introduction of foreign CA activity resulted in the increase of leaf area and dry weight in high light intensity conditions in which the carbon fixation process is the limiting factor of PCA.These results suggested that the introduction of the foreign CA activity in the mesophyll cytoplasm may improve the PCA activity and growth rate, especialy under the CO_2 limiting condition through the reduction of the mesophyll resistance for inorganic carbon transfer.