Photosynthesis and Carbon Metabolism in Higher Plants and Algae

Dear Colleagues,

Photosynthesis, the process via which autotrophs consume carbon dioxide in the green cells, is the most important phenomena on Earth since it provides molecular oxygen and facilitates growth in higher plants and algae by allowing them to utilize organic substances from inorganic carbon. Inorganic carbon is the substrate of the key reaction in the dark stage of photosynthesis, involving the carboxylation of ribulose-1,5-bisphosphate by the enzyme ribulose bisphosphate carboxylase/oxygenase (Rubisco), which is the most abundant plant cell protein. Inorganic carbon is involved not only in the “dark metabolism” reactions, but also interacts with the participants in the “light stage by the effect of HCO₃ˉ (or CO₂) on electron transfer both on the donor and on the acceptor side of Photosystem II, so-called “bicarbonate effect”.

The flows of carbon dioxide in the cell and the whole organism are rather intense. A delay in inorganic carbon intake can not only slow down the processes of photosynthesis, but also gravely alter the homeostasis of the cell and even cause its death. Hence, certain plants require the mechanisms for inorganic carbon concentration in cells close to Rubisco, when adapting to growth conditions during the evolution of photosynthesis. These metabolic pathways, which differ in different groups of organisms, are called the CO₂-concentrating mechanisms (CCM). Aquatic photoautotrophs (such as cyanobacteria and algae) that lack CCM would be deficient in CO₂ for photosynthesis, because despite the fact that the concentration of CO₂ in water is approximately the same as in air, the rate of its diffusion in water is 1000 times smaller. In terrestrial higher plants, CCM exists in the C4 form of photosynthesis with the primary carboxylation reactions and the Calvin cycle separated in space or in time, as in the case of Crassulacean acid (CAM) metabolism.

This Special Issue aims to collate research papers on all aspects of photosynthesis in higher plants and algae, carbon metabolism, inorganic carbon transport into plants cells and organoids, the physiological sensing of carbon dioxide and bicarbonate, the participation of higher plants and algae enzymes in these processes. We also welcome papers concerning the locations, functions, participation in metabolic processes, isolation, structure of dark metabolism enzymes, bicarbonate transporters from algae and higher plants with C3 and C4 types of CO₂ fixation, new aspects of HCO₃ˉ interaction with the components of Photosystem II, the effect of inorganic carbon on the functioning of electron-transport chain, the expression of bicarbonate-transporter-encoding genes, and the practical use of bicarbonate transporter mutants (i.e., their medical relevance, gene manipulation for developing improved agricultural crops, and their application for reducing atmospheric carbon dioxide levels).

Dr. Natalia N. Rudenko
Dr. Natallia L. Pshybytko
Guest Editors

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• algae
• bicarbonate
• bicarbonate effect
• C3 photosynthesis
• C4 photosynthesis
• CAM metabolism
• carbon fixation
• chloroplasts
• CO₂ concentrating mechanism
• higher plant
• photosynthesis
• rubisco

Title: The freshwater cyanobacterium Synechococcus elongatus PCC 7942 does not require an active external carbonic anhydrase
Authors: Elena V. Kupriyanova; Maria A. Sinetova; David A. Gabrielyan; Dmitry A. Los
Affiliation: К.А. Timiryazev Institute of Plant Physiology, Russian Academy of Sciences, Botanicheskaya street 35, Moscow 127276, Russia
Abstract: Under standard laboratory circumstances, Synechococcus elongatus PCC 7942 lacks the periplasmic carbonic anhydrase (CA), EcaASyn. In this study, a S. elongatus transformant was developed that expressed the homologous EcaACya from Cyanothece sp. ATCC 51142. This additional extracellular CA had no detectable effect on the adaptive responses and physiology of cells under fluctuations mimicking those found in S. elongatus natural habitats: varying CO2 and HCO3– concentrations and ratios; oxidative or light stress; and severe CO2 levels. Under some conditions (Na+ depletion, a drop in CO2), the transformant exhibited a disadvantage over wild type cells. S. elongatus cells lacked their own EcaASyn under all experimental settings. A number of studies have found that S. elongatus has mechanisms that limit the emergence of EcaASyn in the periplasm. Supplementary, for the first time, we present data on the expression pattern of CCM-associated genes during S. elongatus adaptation to the replacement of CO2 with HCO3–, as well as cell transfer to high CO2 (up to 100%). An increase in CO2 concentration is accompanied with the suppression of the NDH-14 system, which was previously assumed to function constitutively.