). Green fluorescence increased ~1.9 times in high light corals and decreased ~1.9 times in low light corals compared with medium light corals. GFP concentration and green fluorescence intensity were significantly correlated. Typical photoacclimation responses in the dinoflagellates were observed including changes in density, photosynthetic pigment concentration and photosynthetic efficiency. Although fluorescent proteins are ubiquitous and abundant in scleractinian corals, their functions remain ambiguous. These results suggest that scleractinian corals regulate GFP to modulate the internal light environment and support the hypothesis that GFP has a photoprotective function. The success of photoprotection and photoacclimation strategies, in addition to stress responses, will be critical to the fate of scleractinian corals exposed to climate change and other stressors.Supplementary material available online at http://jeb.biologists.org/cgi/content/full/213/21/3644/DC1 Key words: acclimation, dinoflagellate, fluorescence, GFP, light, photoprotection, Symbiodinium, symbiosis. THE JOURNAL OF EXPERIMENTAL BIOLOGY 3645Coral GFP photoacclimation isolated from jellyfish and now a widely used tool in cellular and molecular biology (Tsien, 1998). FPs inherently affect the internal light microenvironment of the coral by absorbing high-energy light and emitting lower-energy light. FPs are ubiquitous in scleractinian corals (Alieva et al., 2008;Gruber et al., 2008;Salih et al., 2000) and can constitute a significant portion of the total protein content (up to 14%) .The functions of FPs in corals remain ambiguous and controversial. Hypothesized roles for FPs include photoprotection (Kawaguti, 1944;Salih et al., 2000), photosynthesis enhancement (Kawaguti, 1969), camouflage , antioxidant (BouAbdallah et al., 2006;Palmer et al., 2009b), regulation of symbiotic dinoflagellates Field et al., 2006) and as part of the coral immune response (Palmer et al., 2009a). Corals produce a number of FPs with different spectral properties (Alieva et al., 2008), including FPs that do not emit visible fluorescence, which are often called pocilloporins or GFP-like proteins (Dove et al., 1995;Dove et al., 2001). FPs contribute to the diversity of coral coloration (Dove et al., 2001;Labas et al., 2002;Oswald et al., 2007), and it is possible that dissimilar FPs will have different functions while the same FP could have multiple functions. The principal hypothesis, photoprotection, is weakened by a lack of correlation between FPs and depth (Dove, 2004;Mazel et al., 2003;Vermeij et al., 2002). Recently, variation of exposure to blue light was shown to regulate FP concentration (D'Angelo et al., 2008), suggesting a physiological connection between FPs and the high-energy portion of the light spectrum. In addition, corals with and without the GFP-like proteins can have different ecological and physiological characteristics (Takabayashi and Hoegh-Guldberg, 1995).The objective of this study was to investigate the dynamics of GFP concentration in corals...
The emission spectra of 70 bioluminescent marine species were measured with a computer controlled optical multichannel analyzer (OMA). A 350 nm spectral window is simultaneously measured using a linear array of 700 silicon photodiodes, coupled by fiber optics to a microchannel plate image intensifier on which a polychromator generated spectrum is focused. Collection optics include a quartz fiber optic bundle which allows spectra to be measured from single photophores. Since corrections are not required for temporal variations in emissions, it was possible to acquire spectra of transient luminescent events that would be difficult or impossible to record with conventional techniques. Use of this system at sea on freshly trawled material and in the laboratory has permitted acquisition of a large collection of bioluminescence spectra of precision rarely obtained previously with such material. Among unusual spectral features revealed were organisms capable of emitting more than one color, including: Umbellula magniflora and Stachyptilum superbum (Pennatulacea), Parazoanthus lucificum (Zoantharia), and Cleidopus gloria-maris (Pisces). Evidence is presented that the narrow bandwidth of the emission spectrum for Argyropelecus affinis (Pisces) is due to filters in the photophores.
The population growth of some dinoflagellates is known to be reduced by exposure to fluid flow. The red-tide dinoflagellate Lingulodinium polyedrum was used to examine the effect of growth conditions on flow-induced inhibition of population growth. Three factors were tested: time of exposure relative to the light : dark (LD) cycle, illumination level, and culture growth phase (early vs. late exponential phase). Cultures maintained on a 12 : 12 h LD cycle were exposed to one of two flow conditions: quantified laminar shear produced by Couette flow or unquantified flow generated in shaken flasks. The duration of exposure to flow was 1 h d Ϫ1 for 5-8 d in all experiments; the shear stress in Couette shear experiments was 0.004 N m Ϫ2 . There were many qualitative similarities in the pattern of response to flow in the two hydrodynamic conditions. In both cases, exposure to flow in the last hour of the dark phase resulted in greater reduction of net growth than exposure during the light phase. Cultures grown under lower illumination had proportionally greater reductions in net growth than cultures under higher light. Finally, late exponential phase cultures exhibited much greater reductions in net growth following a given flow exposure than early exponential phase cultures. The higher sensitivity of late exponential phase cultures did not appear to be linked to nutrient limitation or changes in pH of the medium; it may be partially attributed to exudates from late exponential phase cells. These results suggest that the response of red-tide dinoflagellate population growth to in situ turbulence may depend on both environmental conditions and the physiological state of the cells.
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