Effect of CO2 Content in Air on the Activity of Carbonic Anhydrases in Cytoplasm, Chloroplasts, and Mitochondria and the Expression Level of Carbonic Anhydrase Genes of the α- and β-Families in Arabidopsis thaliana Leaves

The carbonic anhydrase (CA) activities of the preparations of cytoplasm, mitochondria, chloroplast stroma, and chloroplast thylakoids, as well as the expression levels of genes encoding &alpha:CA1, &alpha:CA2, &alpha:CA4, &beta:CA1, &beta:CA2, &beta:CA3, &beta:CA4, &beta:CA5, and &beta:CA6, were measured in the leaves of Arabidopsis thaliana plants, acclimated to different CO2 content in the air: low (150 ppm, lCO2), normal (450 ppm, nCO2), and high (1200 ppm, hCO2). To evaluate the photosynthetic apparatus operation, the carbon assimilation and chlorophyll a fluorescence were measured under the same conditions. It was found that the CA activities of the preparations of cytoplasm, chloroplast stroma, and chloroplast thylakoids measured after two weeks of acclimation were higher, the lower CO2 concentration in the air. That was preceded by an increase in the expression levels of genes encoding the cytoplasmic form of &beta:CA1, and other cytoplasmic CAs, &beta:CA2, &beta:CA3, and &beta:CA4, as well as of the chloroplast CAs, &beta:CA5, and the stromal forms of &beta:CA1 in a short-term range 1&ndash:2 days after the beginning of the acclimation. The dependence on the CO2 content in the air was most noticeable for the CA activity of the preparations of the stroma: it was two orders higher in lCO2 plants than in hCO2 plants. The CA activity of thylakoid membranes from lCO2 plants was higher than that in nCO2 and hCO2 plants: however, in these plants, a significant increase in the expression levels of the genes encoding &alpha:CA2 and &alpha:CA4 located in thylakoid membranes was not observed. The CA activity of mitochondria and the expression level of the mitochondrial &beta:CA6 gene did not depend on the content of carbon dioxide. Taken together, the data implied that in the higher plants, the supply of inorganic carbon to carboxylation sites is carried out with the cooperative functioning of CAs located in the cytoplasm and CAs located in the chloroplasts.