Intracellular Localization of Phytochrome

Abstract

My first remark is concerned with the interaction of light and molecules [60]. If electronic oscillations are equally possible in all directions, an incident unpolarized light beam will emerge essentially as it entered the system — except for a phase shift. If, however, the particles or molecules in the system are not isotropic and at the same time ordered, an incident unpolarized light beam will be split, because waves oscillating in one direction will have their phases shifted more than those oscillating in another direction. The net result is that anisotropic molecules which are in an order produce two plane polarized emergent beams. Since these emerge in somewhat different directions, the phenomenon is called double refraction or birefringence. The chief use of this phenomenon in biology is in the inverse fashion (Fig. 29): if we line up the molecules of an anisotropic substance then the refraction of plane polarized light measured along and at right angles to the direction of alignment will tell us even more about the electronic structure of the individual molecule.