UV-B-Induced Inhibition of Photosystem II Electron Transport Studied by EPR and Chlorophyll Fluorescence. Impairment of Donor and Acceptor Side Components

Abstract

Inhibition of photosystem II electron transport by UV-B radiation has been studied in isolated spinach photosystem II membrane particles using low-temperature EPR spectroscopy and chlorophyll fluorescence measurements. UV-B irradiation results in the rapid inhibition of oxygen evolution and the decline of variable chlorophyll fluorescence. These effects are accompanied by the loss of the multiline EPR signal arising from the S2 state of the water-oxidizing complex and the induction of Signal IIfast originating from stabilized Try-Z+. The EPR signals from the QA-Fe2+ acceptor complex, Tyr-D+, and the oxidized non-heme iron (Fe3+) are also decreased during the course of UV-B irradiation, but at a significantly slower rate than oxygen evolution and the multiline signal. The decrease of the Fe3+ signal at high g values (g = 8.06, g = 5.6) is accompanied by the induction of another EPR signal at g = 4.26 that arises most likely from the same Fe3+ ion in a modified ligand environment. UV-B irradiation also affects cytochrome b-559. The g = 2.94 EPR signal that arises from the dark- oxidized form is enhanced, whereas the light inducible g = 3.04 signal that arises from the photo-oxidizable population of cytochrome b-559 is diminished. UV-B irradiation also induces the degradation of the D1 reaction center protein. The rate of the D1 protein loss is slower than the inhibition of oxygen evolution and of the multiline signal but follows closely the loss of Signal IIslow, the QA-Fe2+ and the Fe3+ EPR signals, as well as the release of protein-bound manganese. It is concluded from the results that UV-B radiation affects photosystem II redox components at both the donor and acceptor side. The primary damage occurs at the water-oxidizing complex. Modification and/or inactivation of tyrosine-D, cytochrome b-559, and the QAFe2+ acceptor complex are subsequent events that coincide more closely with the UV-B-induced damage to the protein structure of the photosystem II reaction center.

Effects of Ultraviolet‐B Radiation on Photosystem II of the Cyanobacterium Synechocystis sp. PCC 6083

“…Moreover, the finding that, in Synechocystis, ultraviolet-B radiation depletes the PQ pool, as already observed for plant thylakoids [I 5 1, supports our interpretation that the main ultraviolet-B-induced damage to the protein moiety is targeted to the PSI1 donor side in agreement with previous reports [ 14,IS].…”

Effects of solar radiation on growth, photosynthesis and respiration of marine macroalgae from the Arctic

“…As a consequence the ability of thylakoids to maintain their electrochemical gradient can decrease (Strid et al 1996), and the degradation of essential n~olecules such as the D, protein (Greenberg et al 1989), the water-splitting complex (Vass et al 1996) or ribulose 1,s-bisphosphate carboxilase-oxigenase (Strid et al 1990) can increase. However, macroalgae have developed physiological processes such as dynamic photoinhibition to regulate their photosynthetic activity to adapt to and be protected against temporary excessive radiation (Hanelt 1998).…”

Comparison of Chlorophyll Fluorescence Parameters of Cucumis Sativus and Mentha Piperita Leaves Exposed to Short-Term UV-B Irradiation

“…The photosynthetic process can be affected by UV-B radiation at different levels: for example, changes in plant and leaf morphology that decrease light interception, changes in stomatal function that limit the availability of CO 2 , or enzymes of the carbon fixation pathway. The effects of UV-B radiation on light harvesting and primary photochemical reactions of photosynthetic membranes, particularly on the photosystem II reaction center, have attracted much attention and study (Vass et al 1996;Jansen et al, 2008). Luminescence tests are a good way to study plant susceptibility to UV-B radiation (Schreiber et al, 1994;Skórska, 2000a).…”