Istituto di Biofisica     
Youssef T., Angelini N., Gioffrè D., Sgarbossa A., Lenci F. Effects of electron acceptors on step-up photophobic responses of Blepharisma japonicum. In: Journal of photoscience, vol. 7 (1) pp. 1 - 4. Korean Society of photoscience, 2000.
The photosensory ciliates Blepharisma japonicum and Stentor coeruleus use the hypericin-derived pigments blepharismin and stentorin, respectively, as photoreceptor chromophores. Fluorescence quenching studies have ishown that the first excited singlet state of_hypericin and the purified chromophores blepharismin and stentorin can be deactivated by electron transfer to an acceptor molecule with a `suitable reducing potential [1,2]. This paper reports the result of a series of photobehavioral experiments performed with the aim to ascertain if the same electron acceptors which quench the photoreceptor pigment fluorescence _in vitro n1ay also compete with the native acceptor molecule in its natural physiological environment. Individual cell trajectories were examined before and after light stimulation, in the- presence and in th__e1 absence of potential in vivo" electron acceptors, with a microvideo—recording apparatus. Our data, on Bleplzarisma cells, showed that as the negative reduction potential of the electron acceptor increases, a pronounced decrease in cell photoresponsiveness was detected. A dramatic effect on cell photoresponsiveness was noticed in the presence of 1,4-benzoquinone that has the lowest negative reduction potential. Such an effect on the percentage of photoreacting cells was moderate in the case of 1,4—naphthoquinone, with a relatively higher negative reduction potential. In the presence of benzophenone, which has the highest negative reduction potential, no significant effect on a photoreacting cells was noticed. Our results cansupport the hypothesis that in the pigment granules such a light—induced charge transfer from excited blepharismin to a suitable electron acceptor trigger-s sensory ransduction processes in B. japonicum.
Subject Electron acceptor
Photophobic response
Blepharisma japonicum

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