[The influence of red and blue light on the hill activity of Acetabularia mediterranea chloroplasts].

Hill activity (reduction of trichlorophenol indophenol) of chloroplasts isolated after various times from the unicellular alga Acetabularia mediterranea grown under red light conditions decreases with time. After 2 weeks the amount of Hill activity is only about 30-40% of that at the beginning of the red light treatment. On the other hand, Hill activity of chloroplasts from cells grown under blue light does not change remarkably during the course of the experiment. Transfering cells to blue light after 2 weeks in red light results in an increase of Hill activity within 48-72 hours up to the level of Hill activity in cells grown in blue light.It is concluded that the observed changes in the rate of photosynthesis in red and in blue light (Schaeel and Clauss, 1968) are due to an alteration of the photosynthetic apparatus. Apparently processes are affected which are somehow involved in the light reactions.