Abstract
Evergreen species can store chlorophyll (Chl) even in winter; therefore they can dissipate light energy put into Chls depending on seasons. To examine how they dissipate excess energy at low temperature condition, we examined energy flow by means of steady-state and time-resolved fluorescence. Time-resolved fluorescence spectra (TRFS) of Taxus cuspidate needles were measured with a picosecond time-correlated single-photon counting system. TRFS of summer and autumn needles showed relaxation kinetics similar to that of Arabidopsis thaliana, while those of winter and spring showed different features. In TRFS of winter needles, contribution of photosystem (PS) II fluorescence was quite small, and PSII fluorescence lifetimes were twice shorter than that of A. thaliana, indicating quenching of excitation energy and low accumulation of PSII. In spring, the PSI fluorescence showed excitation wavelength dependence. Both PSI and PSII were modified to dissipate excess energy. We will also discuss about the seasonal change of thylakoid stacking.
