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The coupled-dipole approximation has been used to model polarized light-scattering data obtained from the sperm of the octopus Eledone cirrhosa. Mueller scattering-matrix elements (which describe how a sample alters the intensity and degree of polarization of scattered light) were measured as a function of angle. The sample was modeled as a helical fiber believed to correspond to a DNA protein complex. It was necessary to propose an inherent anisotropy in the polarizability of the fiber in order to fit the data. The direction of the principle axes of the polarizability were determined by comparing the model with experimental data. The results suggest that the 2-nm DNA fibers are perpendicular to the thick fiber that defines the helical geometry of the octopus sperm head.

Light scattering measurements were performed on single, immobilized dinoflagellates as well as on suspensions of the species Prorocentrum micans. The normalized Mueller scattering matrix element S14, which indicates an ability to depolarize circularly polarized light, is reported for both cases. The measurements involving single cells were performed on Prorocemrwn micans, Gonyaulax polyedra, and Crypthecodinium cohnii. The results show that the previously reported large S14 signal is not peculiar to P. micans. Time-dependent measurements of live cultures of P. micans show a large, high-frequency S14 signal. This signal is a diurnal function of the time of day, with a maximum at midnight. Investigations of the relationship between single cell and suspension measurements reveal that the large angle-dependent S14 peaks from immobilized single dinoflagellates are responsible for a large time-dependent S14 sigiial at 900 in suspension measurements. The results of these experiments provide further evidence for the hypothesis that the chromosomes of the dinoflagellates are responsible for the large observed S14 signals. The unusual depolarization properties of dinoflagellates should be considered when using polarized light to enhance image contrast in underwater imaging.

The polarization state of a beam of light is fully described by the four elements of the Stokes vector. How the Stokes vector is transformed upon scattering is described by the sixteen element Mueller scattering matrix. Polarized light scattering provides a useful tool to study macromolecular structure. In particular, measurements of Mueller matrix elements have been used to study chromosome structure; changes in these measured quantities can be used to monitor structure as a function of cell cycle. Such measurements done on helical structures can be compared to theoretical computations to determine the geometrical parameters describing the helix. The matrix elements that are most sensitive to the chiral parameters of the helix are largest when the wavelength of light is of the order of the pitch of the helix. Therefore, polarized light scattering measurements made on DNA plectonemic helices would provide the most information in the far ultraviolet (UV) and x-ray region. The Mueller matrix elements are calculated using the coupled dipole approximation in the orientation average at wavelengths in the visible, ultraviolet, and x-ray regions. Each base-pair of the idealized plectonemic helix is represented by a single dipole. A complex polarizability tensor is assigned to each dipole. Calculations are sensitive to the writhe and polarizability of the DNA molecule.

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