Action Spectra for Step‐Up Photophobic Response in Blepharisma

Abstract

The cells of Blepharisma which possess red pigment (blepharismin) show step‐up photophobic response (temporal ciliary reversal induced by a sudden increase in light intensity). Bleaching of the cells by cold shock raised a threshold light intensity for the response, Oxidation of red pigment that produced blue pigment did not raise the threshold for the response. The action spectrum for the step‐up photophobic response of the cells which possess normal red pigment had peaks at about 580, 540 and 490 nm, a value which coincided with peaks of an absorption spectrum of the red pigment. The absorption spectrum of oxidized pigment (blue pigment) shifted 20 nm toward infrared light. The action spectrum for the response of the cells which possess blue pigment also shifted 20 nm toward infrared light. Results suggest that red pigment might be involved in the step‐up photophobic response. Key words. Blepharismin, ciliary reversal, photoreceptors, photoresponse.

Electron Transfer Fluorescence Quenching of Blepharisma japonicum Photoreceptor Pigments

“…Very recently the structure of oxyblepharismin (OxyBP), the photoreceptor pigment mediating step-up photophobic responses in B. japonicum blue cells (7)(8)(9), has also been determined (10). The proposed molecular structure of oxyblepharismin, resulting from a photoinduced rearrangement and irreversible dehydrogenation of blepharismin, adequately accounts for the resemblance between its absorption spectrum and those of hypericin (HYP) and ST (10) (Fig.…”

“…As far as the functional properties of these photoreceptor pigments are concerned, several experimental lines of evidence have indicated that a light-driven proton translocation process is involved in the early steps of the photosensory transduction chain in both B. japonicum and S. coeruleus (7,(12)(13)(14) and references therein). These findings suggest that protons could be released from the first excited singlet state of the chromophore (14,15), but this hypothesis had to be modified as the results of time resolved fluorescence measurements did not support it (16,17).…”

Blepharismins, produced by the protozoan, Blepharisma japonicum, form ion‐permeable channels in planar lipid bilayer membranes

“…1 ) [2]; these granules are located just beneath the plasma membrane [3,4]. The pigments are considered to function as photoreceptors modulating the photobehavior of the cell [5,6]. Blepharismins have also been reported to be toxic to certain other kinds of protozoa [2] and to kill a variety of protozoa, including predators which actively feed on Blepharisma [7,8].…”

Photoresponse in the Ciliated Protozoan Colpoda cucullus

“…Therefore, ciliates may need to escape illuminated areas for survival (Matsuoka et al 2010). Additionally, blepharismin is believed to function as a photoreceptor, mediating photodispersal (Scevoli et al 1987, Matsuoka et al 1992, Checcucci et al 1993. What is the ecological significance of photodispersal in C. cucullus?…”