"Prior to GC-FAME, approximate lipid concentrations and injection volumes were estimated from chlorophyll contents. Chlorophyll content was quantified in ethanol extracts using the optical density at 654 nm and a specific absorbance coefficient of 39.8 L cm -1 g -1 (Wintermans and de Mots 1965). The chlorophyll/lipid mass ratio was taken as one (Janero and Barrnett 1981; Droppa et al. 1990; Kirchhoff et al. 2002; Kóta et al. 2002). "
[Show abstract][Hide abstract] ABSTRACT: Isoprene emission protects plants from a variety of abiotic stresses. It has been hypothesized to do so by partitioning into cellular membranes, particularly the thylakoid membrane. At sufficiently high concentrations, this partitioning may alter the physical properties of membranes. As much as several per cent of carbon taken up in photosynthesis is re-emitted as isoprene but the concentration of isoprene in the thylakoid membrane of rapidly emitting plants has seldom been considered. In this study, the intramembrane concentration of isoprene in phosphatidylcholine liposomes equilibrated to a physiologically relevant gas phase concentration of 20 μL L(-1) isoprene was less than predicted by ab initio calculations based on the octanol-water partitioning coefficient of isoprene while the concentration in thylakoid membranes was more. However, the concentration in both systems was roughly two orders of magnitude lower than previously assumed. High concentrations of isoprene (2000 μL L(-1) gas phase) failed to alter the viscosity of phosphatidylcholine liposomes as measured with perylene, a molecular probe of membrane structure. These results strongly suggest that the physiological concentration of isoprene within the leaves of highly emitting plants is too low to affect the dynamics of thylakoid membrane acyl lipids. It is speculated that isoprene may bind to and modulate the dynamics of thylakoid embedded proteins.
Journal of Bioenergetics 09/2015; DOI:10.1007/s10863-015-9625-9 · 3.21 Impact Factor
"To measure responses of basal resources in the presence and absence of DOC enrichment, chlorophyll a (chl a) was measured as a surrogate of algal biomass and bacterial production (BP) was measured to estimate bacterial activity during the experiment. Chl a was quantified by passing samples through glass fibre filters (Whatman GF/F), extraction of the Chl a in hot ethanol and measuring the chlorophyll spectrophotometrically on a BiochromUltrospecâ 2100 pro with a 10-cm quartz cuvette (Winterman & de Mots, 1965; Sartory & Grobelaar, 1984). Rates of bacterial production (BP) were determined by incorporation of tritiated leucine (40 nM final concentration) in bacterial protein synthesis (Smith & Azam, 1992; Kirchman, 1993). "
[Show abstract][Hide abstract] ABSTRACT: Humic stress is associated with the widespread and ongoing browning of lakes. Natural landscape gradients in dissolved organic carbon (DOC) potentially result in aquatic communities with different tolerances to humic substances and thus expected contrasting responses to further lake browning.If zooplanktonic species are adapted to different background concentrations of DOC, then we expected that the zooplankton from naturally DOC-rich lakes would maintain higher diversity, biomass and overall density in the face of experimental browning than the zooplankton from DOC-poor lakes. We tested this hypothesis in a common-garden experiment by exposing, in enclosures, zooplankton from replicate DOC-rich and DOC-poor source lakes to simulated browning and to clear water.We conducted a 2 × 2 × 3 factorial-design field transplant experiment with zooplankton from replicate DOC-rich (>8.5 mg L−1) and DOC-poor (<3.5 mg L−1) lakes (Québec, Canada) over eight weeks. There were two fixed effects: water treatment (brown or clear water) and zooplankton source (from DOC-rich or DOC-poor lakes). Lake source was included as a random variable in the model for the response of copepod body size in the enclosures. A substance derived from peat, ‘SuperHume’, was used as a source of DOC.The diversity, biomass and total density of zooplankton from DOC-rich and DOC-poor lakes did not differ upon experimental addition of further DOC. This was despite the presence of different copepod body size phenotypes between source lakes that could have potentially caused different community responses: several dominant species of copepods (Cyclops scutifer, Leptodiaptomus minutus and Tropocyclops prasinus mexicanus) had a larger mean population body size in DOC-rich source lakes than in DOC-poor source lakes. Our findings suggest that the zooplankton from DOC-rich lakes does neither better nor worse than zooplankton from DOC-poor lakes when faced with browning from a humic stressor.
"The number of mature lateral roots was counted under a dissecting microscope after an additional 5 d of growth. Chlorophyll content was assayed according to the method of Wintermans and de Mots (1965). "
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