Emerging roles for carbonic anhydrase in mesophyll conductance and photosynthesis

Abstract

Summary Carbonic anhydrase (CA) is an abundant protein in most photosynthesizing organisms and higher plants. This review paper considers the physiological importance of the more abundant CA isoforms in photosynthesis, through their effects on CO2 diffusion and other processes in photosynthetic organisms. In plants, CA has multiple isoforms in three different families (α, β and γ) and is mainly known to catalyze the CO2 false↔ HCO3- equilibrium. This reversible conversion has a clear role in photosynthesis, primarily through sustaining the CO2 concentration at the site of ribulose‐1,5‐bisphosphate carboxylase/oxygenase (Rubisco). Despite showing the same major reaction mechanism, the three main CA families are evolutionarily distinct. For different CA isoforms, cellular localization and total gene expression as a function of developmental stage are predicted to determine the role of each family in relation to the net assimilation rate. Reaction–diffusion modeling and observational evidence support a role for CA activity in reducing resistance to CO2 diffusion inside mesophyll cells by facilitating CO2 transfer in both gas and liquid phases. In addition, physical and/or biochemical interactions between CAs and other membrane‐bound compartments, for example aquaporins, are suggested to trigger a CO2‐sensing response by stomatal movement. In response to environmental stresses, changes in the expression level of CAs and/or stimulated deactivation of CAs may correspond with lower photosynthetic capacity. We suggest that further studies should focus on the dynamics of the relationship between the activity of CAs (with different subcellular localization, abundance and gene expression) and limitations due to CO2 diffusivity through the mesophyll and supply of CO2 to photosynthetic reactions.

The reduction in leaf area precedes that in photosynthesis under potassium deficiency: the importance of leaf anatomy

“…Different from the middle and lower leaf position, leaves in the upper leaf position showed smaller g m and net photosynthetic rate ( A n ) values in spite of larger S c / S and smaller D chl‐chl . The reason may be that the upper leaves were still in the incomplete development stage, and biochemical functions including the Rubisco enzyme and carbonic anhydrase were not yet fully developed (Tiwari et al ., 2006; Suzuki et al ., 2009; Momayyezi et al ., 2020). For developed leaves, slight K deficiency induced significantly increased mesophyll cell size and dropped f ias ; consequently, S m / S was decreased (Fig.…”

Specific features and assembly of the plant mitochondrial complex I revealed by cryo-EM

“…This domain is formed by a trimeric complex, the carbonic anhydrase (CA). CA are zinc-containing enzymes that catalyze the reversible hydration of CO 2 to HCO 3 − , whose roles are usually carbon fixation and pH maintenance 16 . The carbonic anhydrase activity evolved independently several times during evolution, resulting in several CA enzyme families.…”

Maximum CO2diffusion inside leaves is limited by the scaling of cell size and genome size

“…These two conductances are arranged roughly in series, with gliq acting as a greater limitation to CO2 uptake. While multiple factors, such as membrane permeability 4 , carbonic anhydrase 23 , and chloroplast positioning 24 can be actively controlled over short timescales to regulate gliq, once a leaf is fully expanded, the structural determinants of gias and gliq, which include the sizes and configurations of cells and airspace in the mesophyll, are thought to be relatively fixed 4,22 . Of the various mesophyll traits commonly measured, the three-dimensional (3D) surface area of the mesophyll (SAmes) is thought to be the most important structural determinant of gliq.…”