Allocation of Absorbed Light Energy in Photosystem II in NPQ Mutants of Arabidopsis.

To analyze changes of energy allocation in PSII at non-steady state photosynthesis, the induction and relaxation of non-photochemical quenching of Chl fluorescence was re-evaluated with the use of Arabidopsis thaliana mutants in which the ability to induce non-photochemical quenching was either enhanced (npq2) or suppressed (npq1 and npq4). When dark-treated leaves of the wild type (WT) were illuminated, very high Φ, which represents the loss of excitation energy via non-regulated dissipation, at the beginning of light illumination was gradually decreased to the steady-state level. In contrast, Φ, representing regulated energy dissipation in PSII, was relatively constant after a significant change in the first 10 min. In npq1 and npq4 mutants, lower Φ resulted in much higher Φ than in the WT. Comparison of npq1 and npq4 mutants showed a kinetic difference of two types of non-photochemical quenching. Because non-photochemical quenching calculated as NPQ = F - F')/F' was determined by the interplay between Φ and Φ, NPQ and Φ, both of which represent regulatory heat dissipation, were not linearly correlated. We showed that the kinetics of NPQ formation in the light and relaxation in the dark were affected by drastic changes in Φ We discuss the nature of a high level of Φ at the dark-light transition. We also point out an unavoidable problem of applying the energy allocation model when the F/F value changes during a photoinhibiotry illumination.