Features of photosynthesis in Arabidopsis thaliana plants with knocked out genes encoding chloroplast carbonic anhydrases αCA1 and βCA1

The knockout of either At3g01500 gene, or At3g52720 gene encoding Arabidopsis thaliana βCA1 and αCA1 carbonic anhydrases, respectively led to a lower CA activity of chloroplast stroma preparations from knockout mutant plants αCA1-KO and βCA1-KO compared with the activity of such preparations from wild-type (WT) plants. To identify differences in the photosynthetic characteristics of mutant and WT plants, they were grown in low light (LL, 50-70 µmol quanta∙m⁻²∙s⁻¹, natural conditions) and high light (HL, 400 µmol quanta∙m⁻²∙s⁻¹, stressful conditions). The rate of CO₂ assimilation measured at 400 µmoles quanta∙m⁻²∙s⁻¹ in αCA1-KO and βCA1-KO plants grown in LL was lower than in WT plants; in the circumstances, the rate of photosynthetic electron transport in αCA1-KO plants was lower, while in βCA1-KO plants higher than in WT; the CO₂ content in chloroplasts was lower in βCA1-KO than in both WT and αKA1-KO, where it differed little;
the value of the proton motive force was higher in βCA1-KO, and in αKA1-KO it was lower than in WT due to changes in the ΔpH value. The obtained results suggested that βCA1 facilitates the intake of inorganic carbon into chloroplasts, while αCA1 facilitates the conversion of bicarbonate into CO₂ in chloroplasts stroma for its use in the reaction catalyzed by Rubisco. In αKA1-KO and βCA1-KO, the expression levels of genes encoding other chloroplast CAs were markedly different
from the expression levels of these genes in WT; the patterns of the changes depended on the light intensity during cultivation. The content of hydrogen peroxide in leaves of both αCA1-KO and βCA1-KO plants was higher in LL and lower in HL than in WT. The expression levels of stress marker genes changed similarly in both types of mutant plants. The possible involvement of the chloroplast stroma CAs in the transmission of stress signals in higher plants are discussed.