TY - JOUR
T1 - Photovoltages in suspensions of magnetically oriented chloroplasts
AU - Becker, Joseph F.
AU - Geacintov, Nicholas E.
AU - Swenberg, Charles E.
N1 - Funding Information:
We wish to thank Drs. C. Fowler and B. Kok for their very helpful discussions during the initial experimental phases of this work. We are grateful to Professor M. Pope for many stimulating discussions on the Dember effect. This work was supported by a National Science Foundation Grant PCM 76-14359 and in part by a United States Energy Research and Development Administration contract to the Radiation and Solid State Laboratory, New York University.
PY - 1978/9/7
Y1 - 1978/9/7
N2 - The photovoltage of suspensions of magnetically oriented chloroplasts using polarized light of 680 nm has been measured. The magnitude of the photo e.m.f. depends on the polarization of the light and on its direction of propagation with respect to the oriented thylakoid planes. This photo e.m.f. is qualitatively attributed to the Dember effect which arises when inhomogeneous light absorption gives rise to a gradient of positive and negative charges along →x, where →x is the direction difined by the propagation vector of the light and which is also the direction joining the two electrodes. The photovoltage obtained with the planes of the oriented thylakoids parallel to →x depends on the plane of polarization of the incident light and shows that (1) the magnitude of the photovoltage depends on the absorption coefficient (which itself is polarization dependent) and thus on the magnitude of the charge gradient produced by the inhomogeneously absorbed light, and (2) a charge gradient within the planes of the thylakoids can give rise to the macroscopic photovoltage. While our experimental observations are basically in agreement with those previously reported (Fowler, C.F. and Kok, B. (1974) Biochim. Biophys. Acta 357, 308-318 and Witt, H.T. and Zickler, A. (1973) FEBS Lett. 37, 307-310) for unoriented chloroplasts, their interpretation of the origin of this effect in terms of a transmembrane potential must be modified in view of our results obtained with oriented chloroplasts. The macroscopically observed photovoltage of oriented chloroplasts is due to the creation of charge gradients either parallel or perpendicular to the thylakoid planes by a flash of light, the diffusion of these charges and to differences in the mobilities of the negative and positive charges. This interpretation in terms of the Dember effect is completely consistent with the existence of a transmembrane electric field as proposed by Fowler and Kok, as well as by Witt and Zickler. However, macroscopic measurements of the photovoltage using either oriented or unoriented chloroplast suspensions cannot prove that a transmembrane voltage exists, as previously claimed.
AB - The photovoltage of suspensions of magnetically oriented chloroplasts using polarized light of 680 nm has been measured. The magnitude of the photo e.m.f. depends on the polarization of the light and on its direction of propagation with respect to the oriented thylakoid planes. This photo e.m.f. is qualitatively attributed to the Dember effect which arises when inhomogeneous light absorption gives rise to a gradient of positive and negative charges along →x, where →x is the direction difined by the propagation vector of the light and which is also the direction joining the two electrodes. The photovoltage obtained with the planes of the oriented thylakoids parallel to →x depends on the plane of polarization of the incident light and shows that (1) the magnitude of the photovoltage depends on the absorption coefficient (which itself is polarization dependent) and thus on the magnitude of the charge gradient produced by the inhomogeneously absorbed light, and (2) a charge gradient within the planes of the thylakoids can give rise to the macroscopic photovoltage. While our experimental observations are basically in agreement with those previously reported (Fowler, C.F. and Kok, B. (1974) Biochim. Biophys. Acta 357, 308-318 and Witt, H.T. and Zickler, A. (1973) FEBS Lett. 37, 307-310) for unoriented chloroplasts, their interpretation of the origin of this effect in terms of a transmembrane potential must be modified in view of our results obtained with oriented chloroplasts. The macroscopically observed photovoltage of oriented chloroplasts is due to the creation of charge gradients either parallel or perpendicular to the thylakoid planes by a flash of light, the diffusion of these charges and to differences in the mobilities of the negative and positive charges. This interpretation in terms of the Dember effect is completely consistent with the existence of a transmembrane electric field as proposed by Fowler and Kok, as well as by Witt and Zickler. However, macroscopic measurements of the photovoltage using either oriented or unoriented chloroplast suspensions cannot prove that a transmembrane voltage exists, as previously claimed.
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U2 - 10.1016/0005-2728(78)90152-4
DO - 10.1016/0005-2728(78)90152-4
M3 - Article
C2 - 687614
AN - SCOPUS:0018186381
SN - 0005-2728
VL - 503
SP - 545
EP - 554
JO - BBA - Bioenergetics
JF - BBA - Bioenergetics
IS - 3
ER -