PHOTOMOVEMENT RESPONSES OF THE HETEROTRICHOUS CILIATE Blepharisma Japonicum

Abstract

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.

Photomovement in Motile Microorganisms—ii

“…The action spectrum of the phobic response peaks at about 400 nm and extends from below 340 to about 550 nm; no effect was found in the red region of the spectrum (Kraml and Marwan, 1983). Obviously, the red pigment is not the main photoreceptor since it has a major absorption peak at about 574 nm.…”

“…Hardly any differences were found in photokinesis when the posterior or anterior portions of dissected cells were irradiated showing almost the same dependence on fluence rate saturating at about 3000 Ix. Another indication that the two responses are different is seen in the fact that the phobic response can be inhibited by 1 mM NH: while photokinesis is unaffected (Kraml and Marwan, 1983).…”

TIME‐GATED FLUORESCENCE OF BLEPHARISMIN, THE PHOTORECEPTOR PIGMENT FOR PHOTOMOVEMENT OF Blepharisma

“…(step-up photophobic responses; Diehn et al, 1977) have been observed (Giese, 1981;Kraml and Marwan, 1983 and references therein). On the basis of the action spectra, the photoreceptor responsible for this photoreaction was identified as the pigment blepharismin (BP0H)t (Scevoli et al, 1987), a rneso-naphtho-dianthrone-type molecule (see Fig.…”

Phosducin interacts with the G-protein βγ-dimer of ciliate protozoanBlepharisma japonicumupon illumination

“…In cells exposed to light, dephosphorylation of Pdc occurs as a result of the activation of protein phosphatases (Sobierajska et al, 2005). The dephosphorylation of the Pdc coincides with cell step-up photophobic response to increasing light intensity (light stimulus) (Kraml and Marwan, 1983;Fabczak et al, 1993). The light-avoiding response consists of a delayed cessation of cell forward movement, a short period of backward swimming (ciliary reversal), finally followed by restoration of forward movement, usually in a new direction.…”