Tropic responses of Funaria spores to red light.

The tropic responses of Funaria hygrometrica spores to continuous illumination with red light (610 to 690 mmu) have been studied over the intensity range from 10(-5) through 10(+6) erg/cm(2) second, using both plane polarized light and partial illumination with unpolarized light. From the relative frequency of outgrowth origin in different directions, the following is inferred. (1). The germination direction of chloronemal filaments is directly influenced by red light over this whole intensity range, while that of rhizoids tends to be opposite the chloronema. (2) Three photoreceptor systems direct chloronemal primordia: (a) A low intensity system acting from 10(-5) to 10(-0.5) erg/cm(2) second. It favors their growth from a cell's brightest part(s). Its photoreceptors are disoriented, excited by the electric vector, and probably are dispersed phytochrome molecules. (b) A medium intensity system which acts largely alone only at 10(0.5) erg/cm(2) second but is influential from 10(0) to 10(5) erg/cm(2) second. It likewise favors growth from a cell's brightest part(s); its receptor molecules are also excited electrically, but they are tangentially oriented. (c) A high intensity system which acts alone from 10(5) to 10(6) erg/cm(2) second and is influential down to 10(1) erg/cm(2) second. It favors growth of the chloronemas from a cell's darkest part. Its receptors probably are magnetically excited and tangentially oriented. The polarotropic responses of the chloronemas resemble those directing their origins. One new feature is that under intense (10(6) erg/cm(2) second) plane polarized and vertically directed light, many soon grow to form tight helices.