Blue light but not red light induces a calcium transient in the moss Physcomitrella patens (Hedw.) B., S. & G.

In caulonemal filaments of the moss, Physcomitrella patens, which had been incubated in darkness, 3 s irradiation with blue light (λ_max 450 nm) at fluence rates of 100 μmol m⁻² s⁻¹ and above caused a transient␣increase in cytosolic calcium ion concentration, Ca²⁺]_cyt, which was both intensity- and time-dependent. Measurements of Ca²⁺]_cyt were made using moss transformed with the cDNA for apoaequorin and reconstituting the Ca²⁺-dependent photoprotein aequorin in the cytosol by incubation in coelenterazine.␣In response to blue light at fluence rates of 100–1000 μmol photons m⁻² s⁻¹, Ca²⁺]_cyt increased transiently from a basal level of approximately 50 nM to between 200 and 700 nM. Irradiation with red light did not evoke any measurable change in Ca²⁺]_cyt. The presence of calcium in the incubating medium was not required for the increase in Ca²⁺]_cyt to occur. A mutant strain, gad-139, was identified which required an irradiance of only 1 s to evoke a response. The kinetics showed a delay of approximately 6 s from the beginning of illumination before the beginning of the increase in Ca²⁺]_cyt. The data suggest that the activation of a photoreceptor rather than the direct opening of calcium channels is involved in this blue-light response. Received: 4 December 1997 / Accepted: 4 May 1998