Phototaxis action spectrum

Phototactic action spectra of Phormidium autumnale and Phormidium uncinatum, measured by Nultsch86>89), show prominent maxima in the absorption range of C-phycoerythrin and smaller, but distinct, peaks in the absorption range of C-phyco-cyanin. Red light absorbed by chlorophyll a is not active, while in the blue range absorbedby the Soret band, the action spectrum shows aminimum(Fig. 6). Nultsch87) concluded that biliproteins are photoreceptors of phototaxis, but independently of the photosynthetic electron transport and phosphorylation. 

Fig. 7. Action spectrum of positive phototaxis (circles and solid line) and in vivo absorption spectrum (solid line) of Anabaena variabilis. Abscissa wavelength in nm Ordinates phototactic effect in relative units and absorbance respectively (after Nultsch et al.102))...

Poff, K. L. and Hader, D.-P. (1984) An action spectrum for phototaxis by pseudoplasmodia of Dictyostelium diseoideum. Photoehem. Pho-tohiol. 39, 433M36. 

Watanabe, M. and Furuya, M., Action spectrum of phototaxis in a cryptomonad alga Cryptomonas sp.. Plant Cell. Physiol, 15, 413,1974. 

Johnson, C.H., Kondo, X, and Hastings, J. W., Action spectrum for resetting the circadian phototaxis rhythm in the CW 15 strain of Chlamydomonas. 11. Illuminated cells. Plant Physiol, 97,1122,... 

Cadetti, L., Marroni, F., Marangoni, R., Kuhlmann, H.-W., Gioffre, D., and Colombetti, G., Phototaxis in the ciliated protozoan Ophryoglena flava dose effect curves and action spectrum determination, J. Photochem. PhotobioL B Biol, 57, 41-50, 2000. 

FIGURE 122.4 Action spectrum for the positive phototaxis in Fabrea salina. 

In summary, the body of evidence currently available for F. salina indicates that these cells possess two different types of putative photoreceptors, a rhodopsin-like and a hypericin-hke pigment. The hypothesis that a rhodopsin pigment is responsible for phototaxis is supported by several pieces of evidence based on the similarity of its action spectrum to that of P. bursaria, by the effect of metabohc inhibitors such as hydroxylamine and zaprinast, by gene analysis, and by the suggested effect of Hght on membrane conductance. 

Selbach, M., Hader, D.-R, and Kuhlmann, H.W., Phototaxis in Chlamydodon mnemosyne determination of the illuminance-response curve and the action spectrum, /. Photochem. Photobiol B, 49, 35,1999. 

Several action spectra have been constructed for phototaxis (and photophobic responses) in Eu lena. They are distinctly different from those measured, e.g., in Chlamydomonas and have been suggested to represent the involvement of flavins and pterins. Fluorometric analysis has indicated that pterins, absorbing in the UV-A range of the spectrum with a maximum near 360 nm, function as antenna pigments. Pterins emit at about 450 nm, which corresponds with one of the maxima for flavin absorption. The fluorescence emission of the flavins can be detected at 520 nm (82). Therefore the final photoreceptor is thought to be a flavin. 

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