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Journal of Marine Biology
Volume 2011 (2011), Article ID 483428, 6 pages
http://dx.doi.org/10.1155/2011/483428
Research Article

The Effects of UV Radiation on Chloroplast Clumping and Photosynthesis in the Seagrass Halophila stipulacea Grown under High-PAR Conditions

1Department of Molecular Biology and Ecology of Plants, Tel Aviv University, Tel Aviv 69978, Israel
2The Interuniversity Institute for Marine Sciences, POB 469, Eilat 88103, Israel
3Faculty of Life Sciences, Bar-Ilan University, Ramat Gan 52900, Israel

Received 26 May 2011; Revised 10 July 2011; Accepted 19 July 2011

Academic Editor: Yehuda Benayahu

Copyright © 2011 Yoni Sharon et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract

Since potentially harmful ultraviolet radiation (UVR, 280–400 nm) and high photosynthetically active radiation (PAR, 400–700 nm) are present in the shallow waters of the Gulf of Aqaba where part of the seagrass Halophila stipulacea's population thrives, we examined the effects of high PAR with and without UVR on its photosynthesis and midday chloroplast “clumping phenomenon” (Sharon and Beer 2008). It was found that midday clumping occurred only under high PAR in the presence of UVR, which resulted in a 44% reduction in the absorption cross section (or absorption factor, AF) of the leaves and, accordingly, a parallel lowering of midday electron transport rates (ETR). In addition, UVR had a direct effect on the photosynthetic apparatus by lowering quantum yields and, thus, ETRs, while pigment relations remained unaltered. We conclude that the potentially harmful effects of UVR and high PAR on the photosynthetic apparatus of Halophila stipulacea are mitigated by their activation of chloroplast clumping, which functions as a means of protecting most chloroplasts from high irradiances, including UVR.