Abstract
Dissipation of excess energy, normally expressed as NPQ, occurs not only under stressed conditions but under normal daylight conditions. The xanthophyll cycle and PsbS protonation are postulated to play roles in NPQ formation. In overwintering evergreen species, however, there may be other mechanisms maintaining large NPQ even in low light. Under stress conditions, the damage to PSII occurs faster than repair. The damage in the presence of protein synthesis inhibitors, such as lincomycin, is well explained by 'excess' that denotes the fraction of energy migrating to closed PSII centers, while it has been shown that the primary damage occurs in the manganese cluster and the degree of damage depends on the cumulative photon number. We will show some of our experimental data obtained by using red light that is hardly absorbed by the manganese cluster. Inter-relationships of various fluorescence parameters are also described.
