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

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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.