Plant Biol (Stuttg) 2005; 7(2): 156-167
DOI: 10.1055/s-2005-837471
Research Paper

Georg Thieme Verlag Stuttgart KG · New York

Thermal Dissipation of Light Energy is Regulated Differently and by Different Mechanisms in Lichens and Higher Plants

J. Kopecky1 , M. Azarkovich2 , E. E. Pfündel3 , V. A. Shuvalov4 , U. Heber3
  • 1Institute of Microbiology, Academy of Sciences, Department of Autotrophic Microorganisms, Opatovicky mlyn, 379 81 Trebon, Czech Republic
  • 2Timiriasev Institute of Plant Physiology, Russian Academy of Sciences, Botanicheskaya Ul., 35, 127276 Moscow, Russia
  • 3Julius-von-Sachs-Institute of Biological Sciences, University of Würzburg, Julius-von-Sachs-Platz 2, 97082 Würzburg, Germany
  • 4Institute of Basic Biological Problems, Russian Academy of Sciences, 142290 Pushchino-na-Oke, Moscow Region, Russia
Further Information

Publication History

Received: August 18, 2004

Accepted: December 9, 2004

Publication Date:
09 February 2005 (online)

Abstract

Modulated chlorophyll fluorescence was used to compare dissipation of light energy as heat in photosystem II of homoiohydric and poikilohydric photosynthetic organisms which were either hydrated or dehydrated. In hydrated chlorolichens with an alga as the photobiont, fluorescence quenching revealed a dominant mechanism of energy dissipation which was based on a protonation reaction when zeaxanthin was present. CO2 was effective as a weak protonating agent and actinic light was not necessary. In a hydrated cyanobacterial lichen, protonation by CO2 was ineffective to initiate energy dissipation. This was also true for leaves of higher plants. Thus, regulation of zeaxanthin-dependent energy dissipation by protonation was different in leaves and in chlorolichens. A mechanism of energy dissipation different from that based on zeaxanthin became apparent on dehydration of both lichens and leaves. Quenching of maximum or Fm fluorescence increased strongly during dehydration. In lichens, this was also true for so-called basal or Fo fluorescence. In contrast to zeaxanthin-dependent quenching, dehydration-induced quenching could not be inhibited by dithiothreitol. Both zeaxanthin-dependent and dehydration-induced quenching cooperated in chlorolichens to increase thermal dissipation of light energy if desiccation occurred in the light. In cyanolichens, which do not possess a zeaxanthin cycle, only desiccation-induced thermal energy dissipation was active in the dry state. Fluorescence emission spectra of chlorolichens revealed stronger desiccation-induced suppression of 685-nm fluorescence than of 720-nm fluorescence. In agreement with earlier reports of [Bilger et al. (1989)], fluorescence excitation data showed that desiccation reduced flow of excitation energy from chlorophyll b of the light harvesting complex II to emitting centres more than flow from chlorophyll a of core pigments. The data are discussed in relation to regulation and localization of thermal energy dissipation mechanisms. It is concluded that desiccation-induced fluorescence quenching of lichens results from the reversible conversion of energy-conserving to energy-dissipating photosystem II core complexes.

References

U. Heber

Julius-von-Sachs Institute of Biological Sciences
University of Würzburg

Julius-von-Sachs-Platz 2

97082 Würzburg

Germany

Email: heber@botanik.uni-wuerzburg.de

Editor: H. Rennenberg

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