Dedicated to Prof. D.A. Walker, former director of the Robert Hill Institute of Photosynthesis, University of Sheffield, England, on the occasion of his 82nd birthday.
Photoprotection of reaction centers: thermal dissipation of absorbed light energy vs charge separation in lichens‡
Version of Record online: 28 OCT 2010
Copyright © Physiologia Plantarum 2010
Special Issue: Photoinhibition
Volume 142, Issue 1, pages 65–78, May 2011
How to Cite
Heber, U., Soni, V. and Strasser, R. J. (2011), Photoprotection of reaction centers: thermal dissipation of absorbed light energy vs charge separation in lichens. Physiologia Plantarum, 142: 65–78. doi: 10.1111/j.1399-3054.2010.01417.x
- Issue online: 12 APR 2011
- Version of Record online: 28 OCT 2010
- Accepted manuscript online: 5 OCT 2010 03:11PM EST
- Received 3 August 2010;, revised 16 September 2010
During desiccation, fluorescence emission and stable light-dependent charge separation in the reaction centers (RCs) of photosystem II (PSII) declined strongly in three different lichens: in Parmelia sulcata with an alga as the photobiont, in Peltigera neckeri with a cyanobacterium and in the tripartite lichen Lobaria pulmonaria. Most of the decline of fluorescence was caused by a decrease in the quantum efficiency of fluorescence emission. It indicated the activation of photoprotective thermal energy dissipation. Photochemical activity of the RCs was retained even after complete desiccation. It led to light-dependent absorption changes and found expression in reversible increases in fluorescence or in fluorescence quenching. Lowering the temperature changed the direction of fluorescence responses in P. sulcata. The observations are interpreted to show that reversible light-induced increases in fluorescence emission in desiccated lichens indicate the functionality of the RCs of PSII. Photoprotection is achieved by the drainage of light energy to dissipating centers outside the RCs before stable charge separation can take place. Reversible quenching of fluorescence by strong illumination is suggested to indicate the conversion of the RCs from energy conserving to energy dissipating units. This permits them to avoid photoinactivation. On hydration, re-conversion occurs to energy-conserving RCs.