Carbonic Anhydrases are Upstream Regulators in Guard Cells of CO2-Controlled Stomatal Movements

摘要

The continuing rise in atmospheric CO2 causes closing of stomatal pores in leaves and thus globally affects CO2 influx into plants, water use efficiency and leaf heat stress^–. However, the CO2-binding proteins that control this response remain unknown. Moreover, the cell type that responds to CO2, mesophyll or guard cells, and whether photosynthesis mediates this response are matters of debate^–. We demonstrate that Arabidopsis double mutant plants in the β-carbonic anhydrases, βCA1 and βCA4, display impaired CO2-regulation of stomatal movements and increased stomatal density, but retain functional abscisic-acid and blue-light responses.βCA-mediated CO2-triggered stomatal movements are not, in-first-order, linked to leaf-photosynthesis and can function in guard cells. Furthermore, guard cell βCA-over-expression plants exhibit enhanced water use efficiency. Guard cell-expression of mammalian αCAII complements ca1ca4 shows that carbonic anhydrase-mediated catalysis is an important mechanism for βCA-mediated CO2-induced stomatal closing and patch clamp analyses indicate that CO2/HCO3⁻transfers the signal to anion channel regulation. These findings, together with ht1-2 epistasis analysis demonstrate that carbonic anhydrases function early in the CO2 signalling pathway that controls gas-exchange between plants and the atmosphere.