The movement of Micrasterias thomasiana (Desmidiaceae, Zygnematophyceae) in directed blue light

Abstract

Abstract An action spectrum for the rising reaction, i.e. the rising of cells initially lying horizontally to an upright position, was measured in the desmid Micrasterias thomasiana Archer (Zygnematophyceae). The effectivity of blue light (up to 520 nm) is confirmed, while red light (686–695 nm) gives a weak response. Blue light causes Micrasterias cells to show the following reactions: (1) all 77 strains tested give the rising reaction; however, percentage of cells and velocity of rising vary between strains; (2) blue light from above induces rising, whereas blue light from below causes the cells to settle; (3) in bidirectional irradiation the number of risen cells is intermediate; (4) lateral irradiation with blue light leads to an orientation of standing cells, with the long transverse axis aligned parallel to the light. The interaction of different pigment systems is discussed.