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

In blue light (350-500 nm) the rate of photosynthesis (oxygen evolution) of Acetabularia is almost constant after a short period of transition (Fig. 1). In red light (600-700 nm), however, it decreases within 2-3 weeks almost to zero (compensation point). The photosynthetic apparatus is not damaged irreversibly by red light, because transfering the cell from continuous red light (2 weeks) to continous blue light results in an increase of the rate of photosynthesis within 3 days up to the level in blue light (Fig. 5). Photosynthesis can also be stimulated if continuous red light is interrupted daily by short breaks of blue light. The rate of photosynthesis at the end of the induction period depends upon the amount of blue light per day (Fig. 5 and 6) and is probably proportional to the logarithm of this amount.Cell growth (Figs. 2, 7, 8) and formation of dry matter (Figs. 3, 9) in continuous red light, in blue light and in continuous red light supplemented by blue light is controlled by the rate of photosynthesis under these light condition.