TY - JOUR
T1 - Bicarbonate effects on chlorophyll a fluorescence transients in the presence and the absence of diuron
AU - Vermaas, Wim F.J.
AU - Govindjee,
N1 - Funding Information:
We are grateful to Dr. Christa Critchley for a critical reading of the manuscript and to Drs. Pierre Joliot, Jan Amesz and John Whitmarsh for discussions. This work was supported by a grant from the NSF (PCM 7824532).
PY - 1982/5/19
Y1 - 1982/5/19
N2 - We investigated the effect of HCO-3 addition to CO2-depleted thylakoids by means of fluorescence techniques. (1) In the presence of diuron (3-(3,4-dichlorophenyl)-1,1-dimethylurea), the net reduction of the primary quinone-type electron acceptor (Q) of Photosystem (PS) II is about 2-times faster in the absence of HCO-3 than in its presence, whether normal, heat-treated or NH2OH-treated samples are used. This effect of HCO-3 is, therefore, not on the O2-evolving apparatus. It is, however, interpreted to be due to an influence of HCO-3 on the kinetics of the reduction of Q, perhaps combined with an effect on the back reaction of Q- with P-680+, the oxidized form of the PS II reaction center chlorophyll a. (2) Fluorescence experiments in the absence of diuron indicate that the absence of HCO-3 results in a complete block at the quinone level; the area over the fluorescence induction curve in the absence of HCO-3 was found to be 2.2-times higher in the absence than in the presence of diuron, pointing to a complete block of BH2 oxidation in the absence of HCO-3. (3) No change in the midpoint potential of Q is observed when HCO-3 is added to CO2-depleted membranes. HCO-3 not only has a large (on/off) effect on the reoxidation of BH2, but also a smaller effect between P-680 and Q. We propose that HCO-3 binding to its specific site in the thylakoid membrane results in a conformational change, allowing normal electron transport between the two photosystems.
AB - We investigated the effect of HCO-3 addition to CO2-depleted thylakoids by means of fluorescence techniques. (1) In the presence of diuron (3-(3,4-dichlorophenyl)-1,1-dimethylurea), the net reduction of the primary quinone-type electron acceptor (Q) of Photosystem (PS) II is about 2-times faster in the absence of HCO-3 than in its presence, whether normal, heat-treated or NH2OH-treated samples are used. This effect of HCO-3 is, therefore, not on the O2-evolving apparatus. It is, however, interpreted to be due to an influence of HCO-3 on the kinetics of the reduction of Q, perhaps combined with an effect on the back reaction of Q- with P-680+, the oxidized form of the PS II reaction center chlorophyll a. (2) Fluorescence experiments in the absence of diuron indicate that the absence of HCO-3 results in a complete block at the quinone level; the area over the fluorescence induction curve in the absence of HCO-3 was found to be 2.2-times higher in the absence than in the presence of diuron, pointing to a complete block of BH2 oxidation in the absence of HCO-3. (3) No change in the midpoint potential of Q is observed when HCO-3 is added to CO2-depleted membranes. HCO-3 not only has a large (on/off) effect on the reoxidation of BH2, but also a smaller effect between P-680 and Q. We propose that HCO-3 binding to its specific site in the thylakoid membrane results in a conformational change, allowing normal electron transport between the two photosystems.
KW - Bicarbonate effect
KW - Chlorophyll
KW - Dichlorophenyldimethylurea
KW - Fluorescence
KW - Photosystem II
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U2 - 10.1016/0005-2728(82)90012-3
DO - 10.1016/0005-2728(82)90012-3
M3 - Article
AN - SCOPUS:0346130850
SN - 0005-2728
VL - 680
SP - 202
EP - 209
JO - BBA - Bioenergetics
JF - BBA - Bioenergetics
IS - 2
ER -