On the correlation between the amplitude of the electrochromic absorption changes and the number of bulk pigments

A correlation between the amplitude of the electrochromic absorption changes measured at 480 nm and 520 nm and the size of the photosynthetic unit is found. Three tobacco mutants which differ with respect to their photosynthetic unit size exhibit decreased amplitudes of the electrochromic absorption changes which parallel the size of the photosynthetic units. Under these conditions the ATP-yield per flash is unaffected by the photosynthetic unit size. From this it is deduced that the correlation between the amplitude of the electrochromic absorption change and the photosynthetic unit size is due to the fact that the number of pigments undergoing an electrochromic bandshift is proportional to the total pigment content. As the influence on the electrochromic effect at 520 nm is too pronounced as to be simply explainable by the variation of the carotenoid content in the different mutants it is inferred that either structural effects leading to a modification of the carotenoid orientation in the mutants or an indirect influence of chlorophyll on the electrochromic bandshift which depend on the number of chlorophyll molecules are responsible.