Light-stimulated respiration in the green alga Dunaliella tertiolecta: Involvement of the ultraviolet/blue-light photoreceptor(s) and phytochrome?

Starch breakdown and respiratory O2 uptake in the green alga Dunaliella tertiolecta (Butcher) are stimulated not only by blue, but also by red light. In the present study, attempts are described to identify the photoreceptor(s) involved. Fluence rate-response curves with different slopes in the ultraviolet (UV)/blue and in the red spectral region as well as differences in the kinetics and in the influence of dark pre-incubation on the stimulation of respiratory O2 uptake by blue and red light strongly indicate the action of two photoreceptors. Since the effect of red light shows some far-red reversibility, and since simultaneous irradiation with red and far-red light decreases the effectiveness of red light, the involvement of phytochrome — in addition to the UV/blue photoreceptor(s) — is suggested in the light-stimulated respiration in Dunaliella.