UV-B-induced inhibition of photosystem II electron transport studied by EPR and chlorophyll fluorescence. Impairment of donor and acceptor side components

被引:122
作者
Vass, I
Sass, L
Spetea, C
Bakou, A
Ghanotakis, DF
Petrouleas, V
机构
[1] UNIV CRETE, DEPT CHEM, IRAKLION, GREECE
[2] NATL CTR SCI RES DEMOKRITOS, INST SCI MAT, GR-15310 ATHENS, GREECE
关键词
D O I
10.1021/bi9530595
中图分类号
Q5 [生物化学]; Q7 [分子生物学];
学科分类号
071010 ; 081704 ;
摘要
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 S-2 state of the water-oxidizing complex and the induction of Signal IIfast originating from stabilized Tyr-Z(+), The EPR signals from the Q(A)(-)Fe(2+) 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 DI protein loss is slower than the inhibition of oxygen evolution and of the multiline signal but follows closely the loss of Signal IIslow, the Q(A)(-)Fe(2+) 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 Q(A)Fe(2+) 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.
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页码:8964 / 8973
页数:10
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