Journal Article

UV-A Induces Two Calcium Waves in <i>Physcomitrella patens</i>

Edward B. Tucker, Michelle Lee, Shaan Alli, Vinoud Sookhdeo, Masamitsu Wada, Takato Imaizumi, Masahiro Kasahara and Peter K. Hepler

in Plant and Cell Physiology

Published on behalf of Japanese Society of Plant Physiologists

Volume 46, issue 8, pages 1226-1236
Published in print August 2005 | ISSN: 0032-0781
Published online August 2005 | e-ISSN: 1471-9053 | DOI: http://dx.doi.org/10.1093/pcp/pci131
UV-A Induces Two Calcium Waves in Physcomitrella patens

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Our understanding of the role of Ca2+ 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 µW cm–2 at 340 nm for 1,000 ms plus 30 µW cm–2 at 380 nm for 1,000 ms) [abbreviated as 1,000 ms (340/380 nm)] and demonstrated two intracellular waves: a Ca2+ 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 µm 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 µm s–1 and duration of 25.3 ± 4.9 s. Subsequent Ca2+ spikes of similar magnitude followed these waves. The amplitude of the Ca2+ 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 Ca2+ spikes occurred in WT and Ppcry1a/1b but not in PpphotA2/B1/B2. When Mn2+ was added to the culture medium, the [Ca2+]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 [Ca2+]cyt. The characteristics of these Ca2+ waves were dependent upon cryptochrome and phototropin. Blue/UV-A signaling in P. patens appears to differ from that in Arabidopsis.

Keywords: Calcium; Cryptochrome; Phototropin; Physcomitrella patens; UV-A/blue light signaling; [Ca2+]cyt, cytoplasmic calcium concentration; Ca2+ext, external calcium; DIC, differential interference contrast; ER, endoplasmic reticulum; WT, wild type

Journal Article.  7740 words.  Illustrated.

Subjects: Biochemistry ; Molecular and Cell Biology ; Plant Sciences and Forestry

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