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JXB Advance Access published online on October 18, 2006
Journal of Experimental Botany, doi:10.1093/jxb/erl154
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© 2006 The Author(s). This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/2.0/uk/) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.
Received May 17, 2006
Accepted August 3, 2006

RESEARCH PAPER

Impact of ultraviolet radiation on cell structure, UV-absorbing compounds, photosynthesis, DNA damage, and germination in zoospores of Arctic Saccorhiza dermatodea

Michael Y. Roleda 1 *, Christian Wiencke 2, and Ulrike H. Lüder 2

1 Biologische Anstalt Helgoland, Alfred Wegener Institute for Polar and Marine Research, Marine Station, Postfach 180, D-27483 Helgoland, Germany
2 Alfred Wegener Institute for Polar and Marine Research, Am Handelshafen 12, D-27570 Bremerhaven, Germany

* To whom correspondence should be addressed.
Michael Y. Roleda, E-mail: mroleda{at}awi-bremerhaven.de


  Abstract

Stratospheric ozone depletion leads to enhanced UV-B radiation. Therefore, the capacity of reproductive cells to cope with different spectral irradiance was investigated in the laboratory. Zoospores of the upper sublittoral kelp Saccorhiza dermatodea were exposed to varying fluence of spectral irradiance consisting of photosynthetically active radiation (PAR, 400-700 nm; =P), PAR+UV-A radiation (UV-A, 320-400 nm; =PA), and PAR+UV-A+UV-B radiation (UV-B, 280-320 nm; =PAB). Structural changes, localization of phlorotannin-containing physodes, accumulation of UV-absorbing phlorotannins, and physiological responses of zoospores were measured after exposure treatments as well as after 2-6 d recovery in dim white light (8 µmol photon m-2 s-1). Physodes increased in size under PAB treatment. Extrusion of phlorotannins into the medium and accumulation of physodes was induced not only under UVR treatment but also under PAR. UV-B radiation caused photodestruction indicated by a loss of pigmentation. Photosynthetic efficiency of spores was photoinhibited after 8 h exposure to 22 and 30 µmol photon m-2 s-1 of PAR, while supplement of UVR had a significant additional effect on photoinhibition. A relatively low recovery of photosystem II function was observed after 2 d recovery in spores exposed to 1.7x104 J m-2 of UV-B, with a germination rate of only 49% of P treatment after 6 d recovery. The amount of UV-B-induced DNA damage measured as cyclobutane-pyrimidine dimers (CPDs) increased with the biologically effective UV-B dose (BEDDNA). Significant removal of CPDs indicating repair of DNA damage was observed after 2 d in low white light. The protective function of phlorotannins has restricted efficiency for a single cell. Within a plume of zoospores, however, each cell can buffer each other and protect the lower layer of spores from excessive radiation. Exudation of phlorotannins into the water can also reduce the impact of UV-B radiation on UV-sensitive spores. The results of this study showed that the impact of UVR on reproductive cells can be mitigated by protective and repair mechanisms.

Keywords: Cyclobutane-pyrimidine dimers; germination; photosynthesis; ultraviolet radiation; UV-absorbing compounds.
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