JXB Advance Access originally published online on July 3, 2007
Journal of Experimental Botany 2007 58(11):2745-2759; doi:10.1093/jxb/erm139
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
© 2007 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.
This paper is available online free of all access charges (see http://jxb.oxfordjournals.org/open_access.html for further details)
RESEARCH PAPER |
Activation of mechanisms of photoprotection by desiccation and by light: poikilohydric photoautotrophs*
1Julius-von-Sachs-Institute of Biological Sciences, University of Würzburg, Julius-von-Sachs-Platz 2, D-97082 Würzburg, Germany
2Timiriasev Institute of Plant Physiology, Russian Academy of Sciences, 127276 Moscow, Russia
3Institute of Basic Biological Problems, Russian Academy of Sciences, 142292 Pushchino-na-Oke, Moscow Region, and Laboratory of Biophysics, Belozersky Institute of Chemical and Physical Biology, Moscow State University, Moscow 119992, Russia
To whom correspondence should be addressed. E-mail: heber{at}botanik.uni-wuertzburg.de
Mechanisms of protection against photo-oxidation in selected desiccation-tolerant lichens and mosses have been investigated by measuring loss of light absorption during desiccation and chlorophyll fluorescence as indicators of photoprotection. Apparent absorption (1–T) spectra measured in the reflectance mode revealed stronger absorption of photosynthetic pigments in hydrated than in desiccated organisms, but differences were pronounced only in a cyanolichen, less so in some chlorolichens, and even less in mosses. Since the amplitude of chlorophyll fluorescence is a product of (1–T) light absorption by chlorophyll and quantum yield of fluorescence, and since fluorescence is inversely related to thermal energy dissipation, when chemical fluorescence quenching is negligible, fluorescence measurements were used to measure changes in energy dissipation. Preincubation of the hydrated organisms and desiccation in darkness excluded the contribution of mechanisms of energy dissipation to photoprotection which are dependent on the presence of zeaxanthin or on the light-dependent formation of a quencher of fluorescence within the reaction centre of photosystem II. Fast drying in darkness or in very low light was less effective in decreasing chlorophyll fluorescence than slow drying. Heating the desiccated organisms increased fluorescence by inactivating the mechanism responsible for fluorescence quenching. Glutaraldehyde inhibited fluorescence quenching during desiccation. Prolonged exposure of a desiccated moss or a desiccated lichen to very strong light caused more photo-induced damage after fast drying than after slow drying. The photo-oxidative nature of damage was emphasized by the observation that irreversible loss of fluorescence was larger in air than in a nitrogen atmosphere. It is concluded from these observations that desiccation-induced conformational changes of a chlorophyll protein complex result in the fast radiationless dissipation of absorbed light energy. This mechanism of photoprotection is more effective in preventing photo-oxidative damage than other mechanisms of energy dissipation which require light for activation such as zeaxanthin-dependent energy dissipation or quencher formation within the reaction centre of photosystem II.
Key words: Chlorophyll fluorescence, conformational changes, energy dissipation, lichens, mosses, photoprotection, photosystems II and I, reaction centre
* Dedicated to Professor Otto-Ludwig Lange on the occasion of his 80th birthday.
Received 2 March 2007; Revised 24 May 2007 Accepted 28 May 2007