UV-A induces two calcium waves in Physcomitrella patens

Our understanding of the role of Ca(2+) in blue/UV-A photoreceptor signaling in a single cell is limited. Insight into calcium signaling has now been attained in Physcomitrella patens and its cryptochrome and phototropin knock-outs. Physcomitrella patens caulonemal filaments grow in the dark by apical extension and their apical cells are highly polarized. Fura-2-dextran ratio images of the apical cell from wild type (WT), Ppcry1a/1b and PpphotA2/B1/B2 were obtained immediately following UV-A exposure (30 mu W cm(-2) at 340 nm for 1,000 ms plus 30 mu W cm(-2) at 380 nm for 1,000 ms) [abbreviated as 1,000 ms (340/ 380 nm)] and demonstrated two intracellular waves: a Ca(2+) wave from the growing apical tip through the apical cap, and a wave from the junction of the neighboring cell through the vacuolar, nuclear and plastid regions. In WT, the UV-A-induced tip wave increase had a magnitude of 454.0 +- 40 nM, traveled at a rate of 3.4 +- 0.7 mu m s(-1) and was complete within 26.6 +- 2.3 s, while the basal vacuolar wave had a magnitude of 596.8 +- 110 nM, a rate of 8.4 +- 0.8 mu m s(-1) and duration of 25.3 +- 4.9 s. Subsequent Ca(2+) spikes of similar magnitude followed these waves. The amplitude of the Ca(2+) waves in the apical cap and basal vacuolar regions of Ppcry1a/1b were higher than those in the WT, while the duration of those in PpphotA2/B1/B2 was longer. Subsequent Ca(2+) spikes occurred in WT and Ppcry1a/1b but not in PpphotA2/B1/B2. When Mn(2+) was added to the culture medium, the [Ca(2+)]cyt increase was delayed, did not move as a wave and lasted longer. The results indicate that plants respond to blue light and UV-A radiation by generating a wave of changes in the [Ca(2+)]cyt. The characteristics of these Ca(2+) waves were dependent upon cryptochrome and phototropin. Blue/UV-A signaling in P patens appears to differ from that in Arabidopsis.