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1Author    Merope Tsimilli-Michaelab, Martin Pêcheux3, RetoJ. Strasser3Requires cookie*
 Title    Light and Heat Stress Adaptation of the Symbionts of Temperate and Coral Reef Foraminifers Probed in Hospite by the Chlorophyll a Fluorescence Kinetics  
 Abstract    Since the early 80's massive bleaching affects the reef ecosystem. It involves, besides corals, several other species among which large foraminifers, and it corresponds to the loss of their photosynthetic symbionts or the symbionts' pigments. The cause is unclear, though temper­ ature elevation and strong irradiation have been considered to be primary factors. In this work we investigated in two genera of coral reef foraminifers (Amphistegina lobifera and Amphisorus heimprichii) and in the temperate foraminifer Sorites variabilis the response of photosystem II (P SII) of their symbionts in hospite upon light stress (white light of 550 |aE n r 2 s_1 and red light of 3200 |iE m~2 s" 1) and heat stress (up to 32 °C), by means of the Chla fluorescence transients O -J-I-P they exhibit upon illumination. The transients were analysed according to the JIP-test which leads to the calculation of several structural and functional parameters providing a quantification of PSII behaviour. We observed that the various parameters undergo modifications that differ concerning both their extent and their degree of elasticity, thus indicating that different adaptive strategies are employed in response to stress. The most pronounced of these regulatory changes is a wide decrease of the quantum yield of electron transport. However, the extent of the changes, different for the three studied species, was in general smaller when the cultures were kept under low light (70 ^iE m -2 s-1) than in darkness. By the applied stressors, PSII was not damaged and, except for some cells in which an expulsion of symbionts was initiated, no bleaching was observed. This can be well correlated with the observed adaptability of PSII. As a working hypothesis, it is proposed that the decrease of the capacity for electron transport activity might be among the factors trigger­ ing bleaching in the field. 
  Reference    Z. Naturforsch. 54c, 671 (1999); received November 10 1998 
  Published    1999 
  Keywords    Coral-Reef Bleaching, Electron Transport Activity, JIP-test, Photosystem II, Thermoprotection 
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 TEI-XML for    default:Reihe_C/54/ZNC-1999-54c-0671.pdf 
 Identifier    ZNC-1999-54c-0671 
 Volume    54