Phototaxis and Phototropism

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

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. 

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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. 

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... 

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. 

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

Other functions of carotenoids are briefly mentioned here. These include phototropism and phototaxis, reproduction, camouflage colour, precursor role of neoxanthin (38, Fig. 16) for the plant growth hormone abscisic acid and the ant repellent grasshopper ketone [18,41], and cell-cell communication [49], In recent years the function of zeaxanthin (15) and lutein (25) in the human retina has received much attention, cf. the section on Health aspects. 

Phototaxis is the behavior that involves orientation in response to Hght stimuli that carry the information. This behavior consists of a migration oriented with respect to the stimulus direction, which is estabhshed and maintained by direct turns. (Phototaxis is different from phototropism. Phototropism is frequently used for the behavior in which the organisms respond to the Hght with an oriented growth.) Photokinesis is the behavior that comprises undirected responses dependent on the intensity or temporal changes in intensity of the stimulus. 

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