Update: carbonic anhydrases in plants, algae, and cyanobacteria

Area of Science:

• Plant Physiology
• Algal Physiology
• Biochemistry

Background:

• Carbonic anhydrase (CA) is an enzyme critical for carbon dioxide and bicarbonate interconversion.
• Previous assumptions about CA functions in plants, such as pH regulation and CO2 delivery to Rubisco in C3 photosynthesis, are re-evaluated.
• The established roles of CA in CO2 concentrating mechanisms (CCMs) are acknowledged.

Purpose of the Study:

• To review and update the understanding of carbonic anhydrase physiological roles in plants and algae.
• To highlight newly observed and under-appreciated functions of CA.
• To detail CA involvement in C4 photosynthesis and CCMs in various organisms.

Main Methods:

• Literature review and synthesis of existing research on carbonic anhydrase.
• Analysis of physiological data related to CA function in plants and algae.
• Comparative examination of CA roles across different photosynthetic pathways and organisms.

Main Results:

• Carbonic anhydrases do not regulate pH within plant cells nor directly supply CO2 to Rubisco in C3 photosynthesis.
• A key, under-appreciated role of CA is supplying bicarbonate for various carboxylases involved in biosynthesis (nucleotide, fatty acid, amino acid).
• CAs are essential for the operation of CCMs in C4 plants, cyanobacteria, and eukaryotic algae.

Conclusions:

• Carbonic anhydrases have diverse and essential physiological roles in plants and algae beyond previously assumed functions.
• The enzyme's role in bicarbonate supply for biosynthesis is crucial and warrants further attention.
• Understanding CA function is vital for comprehending C4 photosynthesis and CCMs in various photosynthetic organisms.