Edited by: Fabricio Eulalio Leite Carvalho, Corporación Colombiana de Investigación Agropecuaria (AGROSAVIA) – CI La Suiza, Colombia
Reviewed by: Alexander G. Ivanov, Institute of Biophysics and Biomedical Engineering, Bulgarian Academy of Sciences, Bulgaria; Yugo Lima-Melo, Federal University of Rio Grande do Sul, Brazil
This article was submitted to Plant Physiology, a section of the journal Frontiers in Plant Science
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Chloroplast NAD(P)H dehydrogenase (NDH) complex, a multiple-subunit complex in the thylakoid membranes mediating cyclic electron transport, is one of the most important alternative electron transport pathways. It was identified to be essential for plant growth and development during stress periods in recent years. The NDH-mediated cyclic electron transport can restore the over-reduction in stroma, maintaining the balance of the redox system in the electron transfer chain and providing the extra ATP needed for the other biochemical reactions. In this review, we discuss the research history and the subunit composition of NDH. Specifically, the formation and significance of NDH-mediated cyclic electron transport are discussed from the perspective of plant evolution and physiological functionality of NDH facilitating plants’ adaptation to environmental stress. A better understanding of the NDH-mediated cyclic electron transport during photosynthesis may offer new approaches to improving crop yield.
Regulation of photosynthetic electron transport in the thylakoid membrane of chloroplasts is fundamental for the maximum photosynthetic yield and plant growth. The light reactions in photosynthesis convert light energy into chemical energy in the forms of ATP and NADPH. The reactions involve two types of electron transport in the thylakoid membrane. While linear electron transport generates both ATP and NADPH, cyclic electron transport around photosystem I (PSI) is exclusively involved in ATP synthesis without the accumulation of NADPH (
The type I NADH dehydrogenase (NDH-1) is a multisubunit complex located in the thylakoid membrane (
The functional and structural multiplicity of the Cyanobacteria NDH-1 complexes. NDH-1L and NDH-1L′ are involved in respiration and cyclic electron transport around PSI, while NDH-1MS and NDH-1MS′ are involved in the absorption of CO2 and cyclic electron transport around PSI, in which NDH-1MS is a low CO2-induced CO2 absorption complex and NDH-1MS’ is a constitutive CO2 absorption complex (adapted from
The chloroplast NDH complex, located in the thylakoid membrane, mediates CET and chloroplastic respiration (
The structure of the chloroplast NDH complex. SubA, subcomplex A; SubB, subcomplex B; SubM, membrane subcomplex; SubL, lumen subcomplex; SubE, electron donor-binding subcomplex; Stroma, thylakoid matrix; Lumen, thylakoid cavity; Lhca5/6, light harvesting pigment protein (adapted from
While examining the NDH-CET from the perspective of plant evolution, we uncovered some salient observations in some phylogenetically primitive organisms.
In
During the evolution of plants from C3 to C4, the expression of NDH increased significantly (
Theoretically, the NADPH/ATP produced by the linear electron transport is deficient for the assimilation of CO2 at different growth stages; the CET pathway, which only produces ATP, but not NADPH, can effectively compensate for this deficiency (
It was found that the concentration of NADPH was higher, and more H2O2 was produced on the acceptor side of PSI, when measuring the NADPH fluorescence kinetics of cyanobacteria NDH mutant (
Generally, PSI is more stable than PSII and less vulnerable to light damage (
Although the energy provided by NDH-CET is lower than that of LET, it still plays a principal role in fine-tuning energy availability in plants. Besides, it plays a significant role in maintaining photosynthetic carbon fixation of algae and higher plants when encountering abiotic stress events. At present, there are several unanswered questions about NDH-CET: namely, the regulation of NDH pathway which affects the efficient operation of photosynthetic apparatus; the activation of its regulatory mechanism under abiotic stress; the electron transfer processes of NDH; and how they might influence the CO2 concentrating mechanism in algae and higher plants. Moving forward, in-depth studies about the NDH-CET pathway are required to improve the light energy utilization efficiency of plants and to further elucidate the mechanism associated with photoprotection. With the availability of newer technology, harnessing these novel and sensitive tools would improve our understanding of the NDH-CET pathway and ultimately help us to improve crop yield and quality.
YL, MM, and JY are responsible for the general overview of the opinions stated in the manuscript. YL, CB, and JY wrote and modified the manuscript. All authors reviewed and approved the final version of the submitted manuscript.
The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.