Effects of ultraviolet-B radiation on primary photophysical process in photosystem II: A fluorescence spectrum analysis

Abstract

To clarify the effects of Ultraviolet-B (UV-B) treatment on the primary energy transfer process in photosynthesis, PSII was exposed to UV-B radiation by two different methods. beside control samples, one are PSII particles isolated from plants that were irradiated each day for 8 h by increased UV-B (on top of natural light), second are PSII particles isolated from non-irradiated plants but exposed only to UV-B in vitro for 30 minutes directly before fluorescence spectrum was tested (the group of CK+UV-B30min). The steady-state fluorescence techniques were used, and Gaussian deconvolution analysis was employed to better identify the spectral changes resulting from UV-B radiation. The results showed that the group of CK+UV-B30min showed obviously fluorescence quenching for the degradation of some proteins in PSII, while the emission of the group of 7 day UV-B exposure was increased. The deconvolution analysis revealed that 30-min UV-B radiation changed the primary energy transfer process from Chlorophyll a (Chl a) to other pigments. However, if UV-B was added to plants for 7 day, photosystem performed overall regulation by re-arrangement of pigment-protein complexes to resist the stress, which not only altered the energy transfer process from Chl a but also Chlorophyll b (Chl b) and Carotenoid (Car).