Blitzlichtinduktion der Chloroplastenbewegung bei Mougeotia: Wirkung unterschiedlicher Spektralbereiche and Polarisationsrichtungen: Induction of Chloroplast Movement in Mougeotia with Light Flashes: Spectral Sensitivity and Action Dichroism

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Summary Phytochrome-mediated chloroplast movement is induced by flashes of red light with a duration of about 3 ms each. If two flashes are given (-double-flash- inductions), they are separated by a dark interval of 20 s. The spectral distribution of the applied flashes has its maximum near 640 nm and 670 nm, respectively. The following results have been obtained: 1) The effect of a single flash is strongly reduced by preirradiation with far-red (FR; Fig. 1). Without FR, 670 nm is double as effective as 640 nm (Fig. 2). 2) In double-flash experiments after saturating FR with the 2nd flash kept constant, 640 and 670 nm are about equally effective when given as a first flash (Fig. 3). The -difference in the spectral sensitivity has been expected: in the first condition (1), we start with part of the phytochrome in the Pfr form. Thus longer wavelength light transforms Pfr back to Pr at the cell flanks, enhancing the intracellular Pfr gradient which is responsible for the chloroplast movement. In the second condition (2), however, the flash can act only on Pr. We conclude that the spectral sensitivity can be used as an indicator to decide whether the flash acts mainly on Pr or on Pfr. 3) In double-flash experiments after saturating FR with the 1st flash kept constant, 640 and 670 nm are equally effective as a second flash (Fig. 5). We conclude: although the first red flash is expected to have transformed some Pr to Pfr, the effect of the second flash is still mainly its action on Pr rather than on Pfr. 4) Polarized red light as a first flash is about equally effective with the electrical vector oriented parallel or perpendicularly to the cell axis (Fig. 7). Only the second flash exhibits the well-known action dichroism in its typical form. We conclude that after saturating FR the first flash acts mainly on unoriented Pr, i. e. -free- phytochrome. The main effect of the first flash is assumed to be -binding- of Pr to Verwendete Abkurzungen: HR (R) = Hellrot (ca. 640 nm); MR = Mittelrot (ca. 670 nm) ; DR (FR) = Dunkelrot (> 700 nm) ; Pr, Pfr = Phytochrom in der Hellrot- bzw. Dunk elrot-absorbierenden Form.