Linear dichroism and orientation of the Phycomyces photopigment.

The greater sensitivity of a cylindrical Phycomyces sporangiophore to blue light polarized transversely rather than longitudinally is a consequence of the dichroism and orientation of the receptor pigment. The abilities of wild type and several carotene mutants to distinguish between the two directions of polarization are the same. The E-vector angle for maximum response relative to the transverse direction is 42 +/- 4 degrees at 280 nm, 7 degrees +/- 3 degrees at 456 nm, and 7 degrees +/- 8 degrees at 486 nm. The in vivo attenuation of polarized light at these wavelengths is very small. The polarized light effect in Phycomyces cannot arise from reflections at the cell surface or from differential attenuations due to internal screening or scattering.