Light‐induced movement responses of the heterotrichous ciliate Blepharisma japonicum were studied by physiological experiments. Two photosensory responses could be identified. A step‐up photophobic response is observed as a very rapid backward movement. Microbeam irradiations of individual cells showed that only the anterior part of the ciliate is able to perceive the light stimulus that mediates the phobic reaction. The action spectrum peaks at approximately 400 nm, which indicates that a blue light receptor is involved.
Positive photokinesis of Blepharisma could be shown as a forward movement that is accelerated by increasing the applied photon fluence rate. The steady state level of the velocity depends highly on wavelength and photon fluence rate of the actinic light. After specific inhibition of the phobic reaction bv 1 m/W NH4+, photokinesis can be induced by microbeam irradiation at any part of the cell.
We isolated two main pigments by thin layer chromatography and characterized them as hypericin‐like compounds: a red pigment that is obviously responsible for the red color of the ciliates (= blepharismin). and a yellow one with maximal absorption near 420 nm. The possible photoreceptor functions of these pigments are discussed.
We could not find in Blepharisma a distinct phototactic behavior which is so typical for the related ciliate Stentor.
Abstract— The kinetics of phytochrome phototransformation from the red‐absorbing form (Pr) to the far‐red‐absorbing form (Pfr) in vivo at 22°C were studied using a double flash apparatus with 1‐ms flashes. Photoconversion by simultaneous flashes of red light saturates at a low Pfr level, indicating the possible attainment of a photoequilibrium between the excitation of Pr and the photoreversion of intermediates in the course of the I‐ms flashes. At saturation energy, simultaneous flashes resulted in about 50% as much Pfr as was produced by saturating irradiation with 5 s red light. Intermediates of the phototransformation pathway were analysed by separating two red or a red and a far‐red flash by variable dark intervals. In both plants phototransformation intermediates with half‐lives < 1 ms occur, but they are too short‐lived to characterize by our method. The subsequent intermediates have half‐lives of about 7 ms and 150 ms in A vena, 2 ms and 10 ms in Mougeotia. The conversion from Pr to Pfr seems to be completed 1 s after the red flash in Avena. In the alga Mougeotia, Pfr formation seems to be finished within only 50 ms after the inducing red flash. The kinetics obtained from physiological and spectrophotometric experiments with Avena mesocotyls are almost identical. These observations indicate that the physiological response corresponds directly to the amount of Pfr produced and not to phototransformation intermediates or “cycling” between Pr and Pfr.
In the green algaMougeotia, the dichroic orientation of the red-absorbing form of phytochrome (Pr) is parallel of the cell surface, whereas the far-red-absorbing form (Pfr) is oriented normal to it. The time course of the change from parallel to normal was investigated by double-flash irradiation with polarized red and far-red light. The results obtained by two different methods indicate that most of the phytochrome intermediates existing in the first 5 ms after the inducing red flash are still oriented parallel to the cell surface, similar to Pr. At increasing intervals between the red and the far-red flashes, more and more phytochrome molecules turn their transition moments to the Pfr orientation. This reaction is finished after approximately 30 ms. We conclude that the change in dichroic orientation of the phytochrome molecules inMougeotia occurs during the last relaxation steps of the intermediates on the way from Pr to Pfr. It cannot be decided yet, whether the first surface-normal phytochrome species is an intermediate or Pfr itself.
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