Photosynthetic Linear Electron Flow Drives CO2 Assimilation in Maize Leaves

Abstract

Photosynthetic organisms commonly develop the strategy to keep the reaction center chlorophyll of photosystem I, P700, oxidized for preventing the generation of reactive oxygen species in excess light conditions. In photosynthesis of C4 plants, CO2 concentration is kept at higher levels around ribulose 1,5-bisphosphate carboxylase/oxygenase (Rubisco) by the cooperation of the mesophyll and bundle sheath cells, which enables them to assimilate CO2 at higher rates to survive under drought stress. However, the regulatory mechanism of photosynthetic electron transport for P700 oxidation is still poorly understood in C4 plants. Here, we assessed gas exchange, chlorophyll fluorescence, electrochromic shift, and near infrared absorbance in intact leaves of maize (a NADP-malic enzyme C4 subtype species) in comparison with mustard, a C3 plant. Instead of the alternative electron sink due to photorespiration in the C3 plant, photosynthetic linear electron flow was strongly suppressed between photosystems I and II, dependent on the difference of proton concentration across the thylakoid membrane (ΔpH) in response to the suppression of CO2 assimilation in maize. Linear relationships among CO2 assimilation rate, linear electron flow, P700 oxidation, ΔpH, and the oxidation rate of ferredoxin suggested that the increase of ΔpH for P700 oxidation was caused by the regulation of proton conductance of chloroplast ATP synthase but not by promoting cyclic electron flow. At the scale of intact leaves, the ratio of PSI to PSII was estimated almost 1:1 in both C3 and C4 plants. Overall, the photosynthetic electron transport was regulated for P700 oxidation in maize through the same strategies as in C3 plants only except for the capacity of photorespiration despite the structural and metabolic differences in photosynthesis between C3 and C4 plants.

Anthocyanins in metabolites of purple corn

“…Independently, light is also an important factor controlling anthocyanin synthesis ( Mancinelli, 1983 ; Byrnes, 2011 ; Pech et al., 2022 ). Anthocyanin synthesis and accumulation in purple maize seedlings are the result of lightinduction ( Gu et al., 2018 ; Shimakawa and Miyake, 2021 ). The Lc (leaf color) gene is an anthocyanin-regulated gene of bHLH (basic/helix-loophelix) in maize.…”

Enhanced Reduction of Ferredoxin in PGR5-Deficient Mutant of Arabidopsis thaliana Stimulated Ferredoxin-Dependent Cyclic Electron Flow around Photosystem I

“…One set of Arabidopsis plants ( Arabidopsis thaliana WT and pgr5 hope1 ) grown under the above growth conditions were used for the simultaneous analysis of Chlorophyll fluorescence, P700, Plastocyanin, and Ferredoxin with CO 2 /H 2 O-exchange reported by the previous study [ 24 ]. The other set different from the above set were used for the simultaneous analysis of the electrochromic shift (ECS) signal with CO 2 /H 2 O-exchange, reported by the previous study [ 56 ].…”

“…Electrochromic shift (ECS) signal with CO 2 /H 2 O-exchange in Arabidopsis plants ( Arabidopsis thaliana WT and pgr5 hope1 ) were simultaneously analyzed by the method reported in the previous study [ 56 ]. The magnitude of the ECS signal was analyzed by DIRK analysis [ 62 , 63 , 64 ] and normalized as follows [ 65 ].…”

Diurnal Response of Photosystem I to Fluctuating Light Is Affected by Stomatal Conductance

“…When stomata were closed at 18:00, ETRII was not affected under low light but decreased by half under high light compared with values obtained at 15:00 (Figure 1E). To analyze the effect of stomatal closure on CEF performance under FL, we evaluated CEF by subtracting ETRII from ETRI in accordance with established published methods [48,49], although Y(I) can be under/over-estimated depending on the redox state of PC [50,51]. Under low light, CEF activation did not differ between 15:00 and 18:00.…”