Volume No. 5 Issue No.: 1 Page No.: 117-133 July-September 2010

 

PHOTOSYSTEM II RESPONSES TO THERMAL AND /OR LIGHT STRESSES OF DISTINCT ENDOSYMBIO-TIC ITS2 SYMBIODINIUM TYPES ISOLATED FROM MARINE ANIMAL HOSTS

 

Ranjeet Bhagooli

Department of Biosciences, Faculty of Science, University of Mauritius, Republic of Mauritius, (MAURITIUS)

 

Received on :

 

ABSTRACT

 

The responses of photosystem II (PSII) functioning to environmental stresses, such as thermal and/or light, of symbiotic dinoflagellates, belonging to Symbiodinium genus, were characterized in isolated state from 9 host species (1 tridacnid, 1 anemone and 7 corals) collected from Zamami Island and Sesoko Island, Okinawa, Japan. Use of chlorophyll fluorescence ratio (dark-adapted Fv/Fm) revealed significant variations in zooxanthellar PSII responses to thermal (26, 29, 32 and 34°C) and/or light (0, 110, 170 μmol quanta m−2 s−1) levels. The internal transcribed spacer region 2 (ITS2) indicated presence of zooxanthellae phylotypes A in Tridacna sp., C in Aiptasia sp., Acropora microphthalma, Pocillopora damicornis, Platygyra ryukyuensis, Stylophora pistillata, Pachyseris rugosa, Galaxea fascicularis, and D in Pavona varians. The photo-physiological responses represented consistent differences of distinct Symbiodinium types based on the sequences of the ITS region 2 (ITS2). Hierarchical cluster analysis of the responses of the PSII to all temperature and/or light treatments showed groups such as D1a (Pavona varians) and C9b (Platygyra ryukyuensis), A6 (Tridacna spp.) and C70 (Aiptasia spp.), C21a (Galaxea fascicularis) and C1 (Stylophora pistillata and Pachyseris rugosa), and C3 (Acropora microphthalma) and C1c (Pocillopora damicornis) in the order of the most to the least tolerant ones. It is noteworthy that C1 ITS2 type zooxanthellae responded similarly irrespective of the hosts (Pachyseris rugosa or Stylophora pistillata) they were isolated from. These data suggest that Symbiodinium ITS2-typing sounds valid to distinguish between thermally tolerant and susceptible ones.

 

Keywords : Coral, Cnidarian, Endosymbionts, Environmental stress, ITS2 types, Photosystem II, Symbiodinium

 

 

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