Acclimation and adaptation to irradiance in symbiotic dinoflagellates. I. Responses of the photosynthetic unit to changes in photon flux density

Abstract

The photosynthetic responses to variations in photon flux density were determined for Symbiodinium microadriaticum, the symbiont of the Caribbean jellyfish Cassiopeia xamachana, S. kawagutii, the symbiont of the Indo-Pacific stony coral Montipora verrucosa, and S. pilosum, the symbiont of the Caribbean zoanthld Zoanthus sociatus. Photosynthetic responses were characterized in terms of cellular pigment content, photosynthesis versus irradiance (P-I) relationships, and number and size of the photosynthetic unit (PSU). Analyses of the responses under 2 Light regimes of 40 and 250 p 0 1 quanta m-' S-' indicate that: (1) the 3 different species cultured under identical conditions possess different photosynthetic characteristics; (2) the 3 species acclimate to low photon flux density by simultaneously increasing the number and size of their PSU; (3) PSU characteristics were not correlated with the parameters of their respechve P-lcurves; (4) the 3 species analyzed have different photoacclimatory capabilities which can be correlated with their respective ecological distribution as endosymbionts. As different species demonstrate characteristic responses, photo-acclunatory adjustment in symbiotic dinoflagellates may be under genetic constraints, and thus may represent photo-adaptation (sensu 0. Bjorkman). As a whole, the results suggest that symbiont photo-adaptation may constitute an important axis of niche diversification for the intact associations.

Symbiodinium necroappetenssp. nov. (Dinophyceae): an opportunist ‘zooxanthella’ found in bleached and diseased tissues of Caribbean reef corals

“…and S. pilosum to changes in photon flux densities. The results are consistent with the interpretation that the three species adjust to changes in the light regime using different mechanisms (see also Iglesias-Prieto & Trench, 1994. Finally, Brading et al (2011) studied the effect of the elevated partial pressure of CO 2 (pCO 2 ) on growth and productivity of these species.…”

In situ photobiology of corals over large depth ranges: A multivariate analysis on the roles of environment, host, and algal symbiont

“…The phototrophic component of the association is thought to play a major role in coral niche occupation. Specifically, Symbiodinium functional diversity has been hypothesized to regulate the vertical distribution of corals (Iglesias-Prieto and Trench 1994;Iglesias-Prieto et al 2004).…”

“…This allows for the extension, within certain genetic constraints, of the limits of environmental tolerance (Iglesias-Prieto and Trench 1994). Several photoacclimation mechanisms have been reported, including cellular photosynthetic pigment quality and quantity variation (Titlyanov 1981).…”

“…Several photoacclimation mechanisms have been reported, including cellular photosynthetic pigment quality and quantity variation (Titlyanov 1981). For instance, amounts of chlorophyllprotein complexes are known to increase as light availability decreases (Iglesias-Prieto and Trench 1997). This increase contributes to the enhancement of light harvesting and contrasts with photoprotective mechanisms, which become active to avoid overexcitation of the photosynthetic system.…”

“…In dinoflagellates, these two forms correspond to diadinoxanthin and its di-epoxide congener, diatoxanthin, respectively (Brown et al 1999;Warner and Berry-Lowe 2006). Photosynthetic processes such as NPQ have been commonly investigated by means of fluorescence measurements of photosystem II (PSII), which are remarkably informative regarding processes that affect both the light-harvesting antennae and electrontransfer chains (Gorbunov et al 2001;Iglesias-Prieto et al 2004). Besides symbiont-driven processes, there are also host-related mechanisms thought to contribute to an efficient photosynthetic activity.…”