Red‐light and blue‐light photoreceptors controlling chlorophyll a synthesis in the red alga Porphyra umbilicalis and in the green alga Ulva rigida

Chlorophyll synthesis is stimulated by red light in the green alga Ulva rigida C. Ag. and in the red alga Porphyra umbilicalis (L.) Kützing. Because the effect of red light showed some far‐red reversibility in successive red and far‐red light treatments, the involvement of phytochrome or a phytochrome‐like photoreceptor is suggested. The extent of the response is dependent on exposure and photon fluence rate of red‐light pulses. In addition to the effect of red light, a strong stimulation of chlorophyll synthesis by blue light was only observed in Ulva rigida. The effect of blue light shows also some far‐red reversibility. In the green alga the accumulated chlorophyll is higher after blue light pulses than after red light pulses. In Porphyra umbilicalis , however, the contrary is observed. In Ulva rigida the involvement of a blue light photoreceptor in addition to phytochrome or a phytochrome‐like photoreceptor is proposed. The different responses to red and blue light in both algae are explained in terms of their adaptation to the natural light environment.