Contribution of PGR5-dependent cyclic electron transport through photosystem I in C3 photosynthesis

Abstract

Cyclic electron transport through photosystem (PS) I has been believe to work in photosynthesis by supply of extra ATP. We investigated contribution of cyclic electron transport in C3 photosynthesis using pgr5, an Arabidopsis thaliana mutant deficient in the ferredoxin-dependent cyclic activity. For comparison of CO₂ assimilation between wild type (WT) and pgr5, we used low-light grown plants showed no difference in growth. Under light-limiting conditions or CO₂-limiting conditions, net CO₂ assimilation in pgr5 was the same as in the WT. Although at higher irradiance under non CO₂-limiting conditions where energy production by cyclic and non-cyclic electron transport limit photosynthesis, net CO₂ assimilation was 14% lower in pgr5 than in the WT, inactivation of PSI occurred in pgr5. We propose two possible functions of the PGR5-dependent pathway: 1) supply of ATP, and 2) lowering of the electron pressure at the accepter side of PSI.