Role of protective and repair mechanisms in the inhibition of
photosynthesis in marine macroalgae

Donat-P. Häder,*a Michael Lebert,a Rajeshwar P. Sinha,a Elena S. Barbieri b and
E. Walter Helbling b

a Institut für Botanik und Pharmazeutische Biologie, Friedrich-Alexander-Universität
Erlangen-Nürnberg, Staudtstr. 5, D-91058 Erlangen, Germany b Estación de Fotobiología Playa Unión & Consejo Nacional de Investigaciones Científicas y
Técnicas (CONICET), Casilla de Correos NЊ 153, (9100) Trelew, Chubut, Argentina Received 25th June 2002, Accepted 9th August 2002
First published as an Advance Article on the web 10th September 2002

The mechanism of photoinhibition was investigated in three representative macroalgal species growing on the coastof Patagonia: the chlorophyte Ulva rigida C. Agardh, the rhodophyte Porphyra columbina Montagne and thephaeophyte Dictyota dichotoma (Huds.) Lamour. Dark adapted specimens were exposed to 15 min unfiltered solarradiation to induce photoinhibition, and subsequently the recovery of the photosynthetic quantum yield wasfollowed for up to 6 h. Photoinhibition is believed to be due to the damage and proteolysis of the D1 protein in thereaction center of Photosystem II. During recovery this protein is resynthesized. In order to prove this hypothesis,inhibitors of the chloroplast protein synthesis, streptomycin and chloramphenicol were applied. Both retardedthe repair process indicating an inhibition of the D1 protein resynthesis during recovery after the damage theyexperienced during light exposure. Some algal groups use the xanthophyll cycle to ameliorate the inhibition byexcessive light. Dithiothreitol, an inhibitor of violaxanthin de-epoxidase, was administered, to impair thexanthophyll cycle. It strongly affected both photoinhibition and recovery even in the red algal species, which donot have the xanthophyll cycle, indicating that this drug has significant side effects and should be used with cautionfor the study of the involvement of this protective cycle in algae. Pigmentation was followed in the three speciesusing absorption spectroscopy of thallus extracts at 665 nm during continuous exposure to natural solar radiationor radiation deprived of the UV component during two days. The results indicated a pronounced variation inpigmentation over time due to bleaching and resynthesis. Solar radiation was monitored during the experimentsin three channels (UV-B, UV-A and PAR) using an ELDONET instrument on site.
ambient solar radiation which increases toward noon and in the
early afternoon hours 4,19 to recover in the late afternoon and
Macroalgae are major biomass producers in marine ecosystems evening hours. During exposure to intense solar radiation populating coastal regions and continental shelves.1 They are
photosynthetic pigment content either decreases 20–24 or
ecologically important for being at the basis of the intricate increases.19,25 Susceptibility of marine macroalgae to visible
food web in the oceans and giving shelter to adult and larval and UV solar radiation is highly variable among species which stages of fish, crustaceans, mollusks and other animals. They results in a specific depth distribution of species, and the pene- are also economically important and are being exploited for tration of solar visible and UV radiation has a decisive role in food production, as fertilizers and raw material for gelling controlling the depth zonation of macroalgae.26–28 Sublittoral
substances such as agar and carragheenan.2
species are generally more sensitive to solar radiation than Living in the intertidal zone, macroalgae are exposed to eulittoral species.4,26,29,30 This can be easily demonstrated by
drastically changing irradiances as well as changes in salinity, transplantation experiments of algae from deep to shallow temperature and desiccation. Since most of the species are waters.31
sessile, they experience a complicated pattern of irradiances The main photoinhibition site is the reaction center of photo- controlled by the diurnal changes and the superimposed tidal system II.32 Recent research indicates that excessive visible or
UV radiation kinks the D1 protein, which controls the electron The thalli can adapt to the widely changing irradiances by transport after the primary photon absorption; this protein is several protective mechanisms. Many macroalgae were found to subsequently removed by proteases 33 resulting in a reduced
be adapted to low light conditions (shade plants) and to shut quantum efficiency of photosynthesis.34 During recovery a new
down the photosynthetic apparatus when exposed to high solar protein is restored; this process is facilitated by a rapid turnover irradiances, which they experience, e.g., when low tide coincides of the protein.35,36
with low solar zenith angles.5,6 One adaptation mechanism
Another protective mechanism against excessive radiation is is photoinhibition, which is a high light-induced reduction the xanthophyll cycle which relies on the thermal dissipation of of the photosynthetic quantum yield.7,8 Photoinhibition can be
excess excitation energy preventing the formation of singlet monitored by measuring photosynthetic oxygen production 9–11
oxygen in the chloroplasts.37 Zeaxanthin formation is also
or by following chlorophyll fluorescence parameters using a involved in an increase in non-photochemical quenching,38,39
pulse amplitude modulated (PAM) fluorometer.12,13 Both tech-
and the xanthophyll cycle was found to play a role in the niques have been used to study photoinhibition in red, green adaptation mechanism to high light conditions.40,41
and brown algae.13–18 Most studied algae in the supralittoral
The aim of the current work was to demonstrate the and eulittoral show a pronounced photoinhibition under involvement of protein synthesis in the recovery of the photo- Photochem. Photobiol. Sci., 2002, 1, 809–814
This journal is The Royal Society of Chemistry and Owner Societies 2002

Source: http://www.efpu.org.ar/PDF_papers/2002/Abs_Hader02_PPS.pdf

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