Light conversion film promotes CO2 assimilation by increasing cyclic electron flow around Photosystem I in Arabidopsis thaliana

Enhancing photosynthetic efficiency in plants exposed to sunlight is an important long-term goal of research aimed at increasing the supply of biomass for renewable bioenergy worldwide. Light conversion film (LCF), which alters the quality of natural incident light, markedly promotes plant growth. To explore the mechanisms underlying the growth-promoting effect of LCF, we compared the photosynthetic performance of Arabidopsis thaliana grown under LCF and under colorless film. The LCF treatment increased electron transport downstream of Cyt b6f by 30.8%. The cyclic electron flow (CEF) around Photosystem I (PSI) significantly increased, as evidenced by the reduced P700 oxidation rate, measured in the absence or presence of 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU), and the increased ferredoxin-dependent plastoquinone reduction activity. In plants grown under LCF, ATP production increased by 26.6%, perhaps due to enhanced CEF around PSI. The contribution of CEF to increased ATP production was confirmed by the finding that the pgr5 mutant, which lacks PGR5-dependent CEF around PSI, did not exhibit increased ATP production under LCF. Therefore, we propose that in A. thaliana, the increase in CEF around PSI is one of the mechanisms by which LCF promotes CO2 fixation.