LIGHT-INTENSITY DISTRIBUTION IN THYLAKOIDS AND THE POLARITY OF THE PHOTOVOLTAIC EFFECT

The spatial organization in photosystems containing chloroplast membranes is such that some of the relevant distances are of the order of the wavelength of the absorbed light. Consequently, interference between incident and reflected light may occur. This paper calculates the heterogeneity to be expected in the resultant light intensity. The pattern is determined by the wavelength-dependent phase shift of light during scattering. We show that in stroma-membranes this heterogeneity may well be responsible for paradoxical polarities of the photovoltaic effect in which flash illumination of a chloroplast suspension generates a macroscopic electric potential opposite to that expected from shading. The grana-stack dimensions are calculated to lead to the classical picture of shading, consistent with a ''normal'' photovoltaic effect. We demonstrate that the simultaneous presence of stroma- and grana-membranes may explain the observed wavelength dependence of the polarity of the photovoltaic effect.