Causes of Color Change in Blue-green Algae

Abstract

The characteristic colors of the different classes of algae and the striking changes in color of individuals (especially among the Cyanophyceae) have compelled the attention of botanists for many years. Engelmann (1883) observed the rate of assimilation of a number of kinds of algae in the different parts of the spectrum. He concluded that they assimilated fastest in light of a color complementary to their own, and suggested that this effect controlled their distribution in nature. Gaidukov (1902) cultivated Cyanophyceae in light from different parts of the spectrum and found that they assumed a color complementary to that of the incident light. This phenomenon he called "complementary chromatic adaptation." However, Oltmanns (1893) grew marine algae in light of different colors and light of different intensities and concluded that the differences in color of the algae depended principally on differences in intensity. A third proposal was made by Schindler (1913) on the basis of experiments on the cultivation of Oscillatoriaceae. He decided that the color of the algae depended primarily on the supply of essential food materials, especially nitrogen compounds, and that the intensity of light influenced only the rate of color change by influencing the rate of the organisms' growth and hence of exhaustion of the medium. A large amount of work has appeared supporting each of the three doctrines. The best discussions of the literature are to be found in Schindler (1913) and Harder (1923). Much of the work done hitherto has been accomplished under unfavorable circumstances. The organisms used have grown slowly or not at all or have died during the experiments (Harder 1922). The color changes have often been slight or have affected only some of the individuals studied (Gaidukov 1902). The experimenters have usually been satisfied to work at low light intensities or in the varying and interrupted light of day (v. Richter 1912, Boresch 1921, Harder 1923). The experiments of which a preliminary report is given below were conducted in the course of developing a standard technique of cultivation which would produce uniform material for work on the photosynthesis of a blue-green alga. The organism used develops vigorously and uniformly under the conditions devised, but if the illumination is varied in the ways described, it exhibits striking color changes. In my opinion the relation of the color changes to changes in the illumination is so clear that the conflicting theories of the past may be judged in its light.