Changes of photosystem II electron transport in the chlorophyll-deficient oilseed rape mutant studied by chlorophyll fluorescence and thermoluminescence

The photosystem II (PSII) complex of photosynthetic membranes comprises a number of chlorophyll-binding proteins that are important to the electron flow. Here we report that the chlorophyll b-deficient mutant has decreased the amount of light-harvesting complexes with an increased amount of some core polypeptides of PSII, including CP43 and CP47. By means of chlorophyll fluorescence and thermoluminescence, we found that the ratio of Fv/Fm, qP and electron transport rate in the chlorophyll b-deficient mutant was higher compared to the wild type. In the chlorophyll b-deficient mutant, the decay of the primary electron acceptor quinones (Q(A)(-)) reoxidation was decreased, measured by the fluorescence. Furthermore, the thermoluminescence studies in the chlorophyll b-deficient mutant showed that the B band (S-2/S(3)Q(B)(-)) decreased slightly and shifted up towards higher temperatures. In the presence of dichlorophenyl-dimethylurea, which is inhibited in the electron flow to the second electron acceptor quinines (OB) at the PSII acceptor side, the maximum of the Q band (S(2)Q(A-)) was decreased slightly and shifted down to lower temperatures, compared to. the wild type. Thus, the electron flow within PSII of the chlorophyll b-deficient mutant was down-regulated and characterized by faster oxidation of the primary electron acceptor quinine Q(A)(-) via forward electron flow and slower reduction of the oxidation S states.