Reversible hydration of carbon dioxide. Required for photosynthesis in cotyledons. Binds salicylic acid. Together with BCA4, involved in the CO(2) signaling pathway which controls gas-exchange between plants and the atmosphere by modulating stomatal development and movements. Promotes water use efficiency. H(+) + hydrogencarbonate = CO2 + H2O Homohexamer. Strongly expressed in aerial tissues including leaves, stems, flowers and siliques. Accumulates in both guard cells and mesophyll cells. Expression reduced by 70% under dark conditions. S-nitrosylation at Cys-280 is up-regulated during nitrosative burst and suppresses both binding of salicylic acid and carbonic anhydrase activity. S-nitrosylated in response to an avirulent but not to a virulent bacterial strain. Reduced levels of seedling establishment associated with altered cotyledon photosynthetic performance at the onset of phototrophic growth and prior to the development of true leaves. These phenotypes are reversed in high CO(2) or sucrose supplemented conditions. Decreased resistance against avirulent bacteria. In plants lacking both BCA1 and BCA4, impaired CO(2)-regulation of stomatal movements associated with reduced beta carbonic anhydrase activity in guard cells, and increased stomatal density. Belongs to the beta-class carbonic anhydrase family. Truncated N-terminus.