Untersuchungen zum Photoreceptorproblem beim tonischen Blaulicht-Effekt der Starklichtbewegung des Mougeotia-Chloroplasten

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Summary If irradiated simultaneously from different directions with blue light of high intensity and with red light of low intensity, the chloroplasts of Mougeotia are oriented by red rather than by short wave length light. The main effect of blue light seems to be, in this case, to change the chloropla sts from a positive to a negative phototact ic response, oriented by phytochrome. Thus, the additional given blue light has a tonic effect, i. e. independent of its direction (SCHONBOHM, 1966 b, 1967 a). It seems to be possible, that the difference between the action spectra of the high intensity movement of Mougeotia-chloroplasts (SCHONBOHM, 1963) and the action spectra of chloroplast movements of other objects (HAUPT, 1963; HAUPT and SCHONBOHM, 1970) is caused by the fact that both photoperception in phytochrome and photoperception in a yellow pigment arc represented by the action spectra of chloroplast movement of Mougeotia obtained when irradiating only with a single radiation source. In the following experiments we will record action spectra for the tonic blue light effect only; we have to take care of the action-dichroism, which we have found in former investigations (SCHCNBOHM, 1968). Polarized red light vibrating perpendicularly (r ⊥ or parallel (r ∥) to the cell axis is given simultaneously with blue light (bl). The following results have been obtained in the present investigations. 1. a) The action spectrum for the tonic effect of unpolarized blue light (bl *. with r ⊥ does not differ remarkably from the action spectra for the high intensity movement induced by blue light only (ef. fig . 2 with fig. 1). b) If we compare the action spectra for the effect of unpolarized blue light (bl *. with or without r ⊥ with the action spectra for the tonic effect of polarized blue light (bl ∥. with r ⊥) in the latter we can see a pl ateau reaching from ca. 450 nm to 470 nm instead of one peak near 465 nm (fig. 4). In the latter action spectra we do not find a relativel y high peak in the near ultraviolet as we did in the former action spectra (bl *, with or without r ⊥). 2. a) It has been demonstrated that polarized blue light (λ : ca. 400-500 nm) is tonically much more effective, if vibrating parallel to the cell axis (bi ∥, with r ⊥ than if vibrating perpendicularly (bl ⊥, wirh r ⊥) (fig. 3). b) This action dichroism is inverse, if Mougeotia is irradiated with ultraviolet light (λ = 363 nm) rather than with polarized visible blue light (λ > 400 nm) (fig. 7). c) If the wavelength of the blue light is longer than 400 nm the action dichroism for the tonic blue light effect remains constant during the whole day, whereas it is changing in a diurnal rhythm in near ultraviolet light (fig. 8). d) Action dichroism for the tonic blue light effect of the high intensity movement of Mougeotia-chloroplasts cannot be caused by an action dichroism of a countercurrent «low intensity movement» which is induced simultaneously by the same intensities of polarized blue light as are needed for high intensity movement (ef. fig. 9 and 10).