Abstract
Carbonic anhydrase, a metalloenzyme which catalyses the reversible interconversion of HCO 3 ? and CO 2 , is a major protein component of higher plant tissues. It is now shown that DNA sequence and encoded proteins for the different ?, ?, ?, ?, ?, and ? forms of carbonic anhydrases are present in living organisms. While there are no sequence homologies between the different type of carbonic anhydrases, all the ?, ?, and ? carbonic anhydrase gene family enzymes in higher plants catalyze the same chemical reaction. Its specific function is generally assumed to convert CO 2 to HCO 3 ? for the phosphoenolpyruvate carboxylase reaction and convert HCO 3 ? to CO 2 for the ribulose-1,5-bisphosphate carboxylase reaction in photosynthesis. Moreover, carbonic anhydrase activity in guard cells is required for CO 2 -mediated stomatal regulation and carbonic anhydrases may provide an approach for plant alternatively protection against stress conditions. Recent studies on carbonic anhydrases described in this manuscript include the characterization and gene family of carbonic anhydrases, physiological function of higher plant CAs, and gene engineerings about higher plant CAs.
Highlights
It is approved that yield potentials of cereal crops cannot further be increased by addition of chemical fertilizer, and photosynthesis increasing could be the major avenue to increase crop yield in 50 years (Surridge, 2002; Reynolds et al, 2009)
The connection between CA and photosynthesis is perhaps the most widely understood roles of plant CA. This role is most important because the uncatalyzed interconversion between CO2 and HCO3− is 104 times slower compared with the flux of CO2 in photosynthesis (Badger & Price, 1994)
It is important that the study on the differ of CAs between C3 plants and C4 plants, and the application of plant CA may contributed to enhance crop photosynthetic efficiency and increase crop yields
Summary
It is approved that yield potentials of cereal crops cannot further be increased by addition of chemical fertilizer, and photosynthesis increasing could be the major avenue to increase crop yield in 50 years (Surridge, 2002; Reynolds et al, 2009). Plant photosynthetic organisms have developed methods for the acquisition of inorganic carbon (Ci) to aid ribulose-1,5-bisphosphate carboxylase (RuBisco) and to enhance CO2 fixation. Carbonic anhydrases often play important roles in this process. CAs has been characterized at catalytic, cellular and tissue levels in all life forms Based on their amino acid sequences, living organism CAs can be categorized into six independent families named as ɑ, β, γ, δ, ε, and ζ (Moroney, Bartlett, & Samuelsson, 2001). The higher plants have developed their versions of photosynthetic CO2 concentrating mechanisms (CCMs) to aid Rubisco in CO2 capture. An important aspect of CCMs is the critical roles of CAs play in the overall process, participating in the interconversion of CO2 and HCO3− both inside and outside the cell. It would be one important research subject to enhance the CO2 assimilation intensity of C4 pathway in C3 plants by the artificially regulation of CA expression
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