Transport and Use of Bicarbonate in Plants: Current Knowledge and Challenges Ahead

Abstract

Bicarbonate plays a fundamental role in the cell pH status in all organisms. In autotrophs, HCO3− may further contribute to carbon concentration mechanisms (CCM). This is especially relevant in the CO2-poor habitats of cyanobacteria, aquatic microalgae, and macrophytes. Photosynthesis of terrestrial plants can also benefit from CCM as evidenced by the evolution of C4 and Crassulacean Acid Metabolism (CAM). The presence of HCO3− in all organisms leads to more questions regarding the mechanisms of uptake and membrane transport in these different biological systems. This review aims to provide an overview of the transport and metabolic processes related to HCO3− in microalgae, macroalgae, seagrasses, and terrestrial plants. HCO3− transport in cyanobacteria and human cells is much better documented and is included for comparison. We further comment on the metabolic roles of HCO3− in plants by focusing on the diversity and functions of carbonic anhydrases and PEP carboxylases as well as on the signaling role of CO2/HCO3− in stomatal guard cells. Plant responses to excess soil HCO3− is briefly addressed. In conclusion, there are still considerable gaps in our knowledge of HCO3− uptake and transport in plants that hamper the development of breeding strategies for both more efficient CCM and better HCO3− tolerance in crop plants.

Insights on the Functions and Ecophysiological Relevance of the Diverse Carbonic Anhydrases in Microalgae

“…CCM components have been described both in marine and freshwater cyanobacteria and recently in cyanobacteria living in alkaline lakes [53]. Most bicarbonate transporters belong to the solute carrier family (SLC) and have been well described in mammals and humans [54]; however, other types of transporters have also been found in photosynthetic organisms.…”

Dynamic expression of intra‐ and extra‐cellular proteome and the influence of epiphytic bacteria for Nostoc flagelliforme in response to rehydration

“…3, cluster 2). As we have known, HCO 3 − plays a fundamental role in the cell pH status and may further contribute to carbon concentration mechanisms (Poschenrieder et al, 2018). Periplasmic component of the Tol biopolymer transport system, this Tolb protein was reported to be related to the stability of the outer membrane by transporting crucial outer membrane components, and could also be induced to maintain the function of the outer membrane as a barrier under heavy metal toxicity (Park and Ely, 2008).…”

Towards a quantitative assessment of inorganic carbon cycling in photosynthetic microorganisms

“…ICC, mediated through components of the carbon concentrating mechanism, can be defined as simultaneous uptake of dissolved carbon dioxide (dCO 2 ) and excretion of bicarbonate (), or vice versa simultaneous uptake and dCO 2 efflux. In cyanobacteria, can enter the cells via the transporters BCT1, SbtA and BicA, and dCO 2 by NDH‐I 3 and NDH‐I 4 . In eukaryotic microalgae, dissolved inorganic carbon (DIC) transporters comprise HLA3, LCIA, possibly LCI1 and CCP1/2 (in Chlamydomonas reinhardtii ), SLC4 and its homologues (in diatoms), and possibly also other transporters in other species .…”

“…In cyanobacteria, can enter the cells via the transporters BCT1, SbtA and BicA, and dCO 2 by NDH‐I 3 and NDH‐I 4 . In eukaryotic microalgae, dissolved inorganic carbon (DIC) transporters comprise HLA3, LCIA, possibly LCI1 and CCP1/2 (in Chlamydomonas reinhardtii ), SLC4 and its homologues (in diatoms), and possibly also other transporters in other species . Once inside the cell, dCO 2 is reduced to by carbonic anhydrase (CA) or CA‐like enzymes, and is transported for DIC assimilation by RuBisCo either to the carboxysome (in cyanobacteria), the pyrenoid (in some algae) or elsewhere in the chloroplast (in other algae).…”

“… channels have been found in plants and have also been proposed for microalgae; for a recent review, see ref. []. Both constitutively transcribed transporters BTC1 and HLA3 require ATP (whereas the transporters SbtA and BicA, induced by low inorganic carbon, require only Na + export, mediated by H + /Na + antiporters such as NhaS3).…”