Fast chlorophyll a fluorescence induction (OJIP) phenotyping of chlorophyll-deficient wheat suggests that an enlarged acceptor pool size of Photosystem I helps compensate for a deregulated photosynthetic electron flow

• Published in: Journal of photochemistry and photobiology. B, Biology Biology, 2022-09, Vol.234, p.112549-112549, Article 112549
• Main Authors: Ferroni, Lorenzo, Živčak, Marek, Kovar, Marek, Colpo, Andrea, Pancaldi, Simonetta, Allakhverdiev, Suleyman I., Brestič, Marian
• Format: Article
• Language: English
• Subjects: Amplitudes; Antennas; Chlorophyll; Chlorophyll-deficient wheat; Deficient mutant; Deregulation; Electron transport; Electron transport chain; Ferredoxin; Fluctuating light; Fluorescence; Oxidoreductase; Parameters; Phenotypes; Phenotyping; Photochemistry; Photosynthesis; Photosynthesis phenotyping; Photosystem I; Photosystem II; Prompt chlorophyll fluorescence; Wheat
• ISSN: 1011-1344; 1873-2682
• DOI: 10.1016/j.jphotobiol.2022.112549

The wheat lines affected by a decrease in the leaf chlorophyll content typically experience a biomass loss. A known major problem of the chlorophyll-deficient wheat mutants is their limited prevention of Photosystem I (PSI) over-reduction brought about by an insufficient cyclic electron flow, potentially exposing them to a higher sensitivity to light fluctuations. However, the resistance of some mutant lines against fluctuating light suggests the occurrence of regulatory processes compensating for the defect in cyclic electron flow. In this study, a phenotyping approach based on fast chlorophyll a fluorescence induction (OJIP transient), corroborated by P700 redox kinetics, was applied to a collection of chlorophyll-deficient wheat lines, grown under continuous or fluctuating light. Quantitative parameters calculated from the OJIP transient are considered informative about Photosystem II (PSII) functional antenna size and photochemistry, as well as the functioning of the entire photosynthetic electron transport chain. The mutants tended to recover a wild-type-like chlorophyll content, and mature plants could hardly be distinguished based on their effective PSII antenna size. Nevertheless, specific OJIP-derived parameters were strongly correlated with the phenotype severity, in particular the amplitude of the I-P phase and the I-P/J-P amplitude ratio, which are indicative of a more capacitive pool of PSI final electron acceptors (ferredoxin and ferredoxin-NADP+ oxidoreductase, FNR). We propose that the enlargement of such pool of electron carriers is a compensatory response operating at the acceptor side of PSI to alleviate potentially harmful over-reduced states of PSI. Our results also suggest that, in chlorophyll-deficient mutants, higher FV /FM cannot prove a superior PSII photochemistry and wider I-P phase is not indicative of a higher relative content of PSI. •Mature wheat mutants have WT-like PSII functional antenna size.•Higher FV/FM does not indicate a superior PSII activity or biomass productivity.•In mutants, electrons flow faster to the end PSI acceptors.•A more capacitive PSI end acceptors pool can help alleviate PSI acceptor-side limitation.•An enlarged PSI end acceptor pool can confer resistance to fluctuating light.