Phototaxis in Plants

Abstract

Publisher Summary Phototaxis is the orientation of free moving organisms to light. In plants, it is restricted to lower organisms, because only among them do we find freely moving organisms. Phototaxis has been reported in bacteria, blue-green algae, diatoms, desmids, and many flagellates. In addition a phototactic response is to be found also in unicellular stages of many higher organized algae and even of some lower fungi, viz., zoospores and gametes. In plants, in lower as well as in higher ones, another quite different possibility of phototactic movement exists: the orientation movement of chloroplasts inside the cell. The majority of plants exhibit chloroplast movement only as long as illumination takes place. Moreover, a certain chloroplast arrangement as a result of a certain illumination is kept unchanged only so long as the illumination is continued. Soon after the illumination is discontinued, the chloroplasts arrange themselves into a special “dark arrangement” or into quite a symmetrical distribution around the whole cell. The chapter discusses the phototaxis of free moving organisms, the relationships of positive and negative phototaxis to each other and their interconversions, and the mechanism of chloroplast movement.