Phototaxis

Flavins (152), benzoamielated derivatives of lumazine (145), are implicated in a variety of photobiological processes such as photodynamic action, phototropism, phototaxis, and photosynthesis. The biologically active H form 152a of alloxazine (R = R = R = = H) is less stable in... 

Phototaxis in photosynthetic bacteria is well illustrated by the behavior... 

Although fragmentary evidence points to a linkage to metabolic processes such as photosynthesis and respiration, the mechanisms of phototaxis and phototropism remain largely unknown and must await the results of further research in this very interesting area. 

Thus far in this book we have discussed one- or two-component photochemical systems which because of their relative simplicity lend themselves quite well to laboratory study. Consequently the mechanisms of many of the photoreactions we have discussed have been elucidated in exquisite detail. As we turn our attention in this chapter to some photochemical aspects of living systems, we shall find much more complex situations in which mechanistic details are just now beginning to be obtained. In some systems, such as those which exhibit phototaxis or phototropism, so little is known that our treatment must as a consequence be limited to only a brief discussion of these phenomena. The topics we will consider here are photosynthesis, vision, phototaxis and phototropism, and damage and subsequent repair of damage by light. Due to space limitations, a discussion of the very fascinating area of bioluminescence must be omitted. 

Phototropism is defined as the directed growth or bending of fixed organisms in response to light. Phototaxis is light-induced locomotion of... 

Song PS and Moore TA. 1974. On the photoreceptor pigment for phototropism and phototaxis Is a carotenoid the most likely candidate Photochemistry and Photobiology 19 435 441. 

Haupt, W. Die Phototaxis der Algen . In Handbuch der Pflanzenphysiologie. Ruhland, W. (ed.), Berlin, Gottingen, Heidelberg Springer 1959... 

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. 

The action spectmm of positive and negative phototaxis of Anabaena variabilis was measured recently106). This species contains no C-phycoerythrin. Accordingly, maximum activity is found at around 615 nm (Fig. 7). In addition, in this form a second maximum occurs at around 675 nm, and a third small, but distinct, one at 440 nm, both indicating that chlorophyll a is also involved in the active light absorption (see above). The utilization via photosynthesis, however, could be excluded in this case, since the trichomes oriented themselves perfectly well to the light direction in the presence of photosynthetic inhibitors, such as DCMU and DBMIB, at concentrations in which the photosynthetic oxygen evolution was almost completely inhibited. 

The situation is further complicated by the finding that in negative phototaxis, radiation between 500 and 560 nm and above 700 nm is effective in addition to the wavelengths, which are active in the positive response. Nultsch et al.106) have discus-... 

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))...

Man ten, A. Phototaxis, phototropism and photosynthesis in purple bacteria and blue-green algae. Thesis, Utrecht, 1948... 

Nultsch, W. Phototaxis and photokinesis in bacteria and blue-green algae. In Behaviour of Microorganisms (Perez-Miravete, A., eds.). London, New York Plenum Press 1973, pp.70-81... 

Nultsch, W. Phototaxis and photokinesis. In Primitive Sensory and Communication Systems The Taxes and Tropisms of Micro-organisms and Cells (Carlile, M.J., ed.). London,... 

Morphological abnormalities, both positive and negative phototaxis suppressed 29... 

No effect on positive phototaxis response of stage IV larvae 35... 

---