Spectrophotometric Characteristics of Chlorophylls a and b and Their Phaeophytins in Ethanol
The absorption spectra of chlorophylls a and b in 96% ethanol, and of pheophytins a and b in 80% ethanol-0.01 N hydrochloric acid have been determined in comparison with known absorption coefficients.
Available from: Kristin J. Painter
- "Due to instrument availability, benthic chl a analysis was conducted using both spectrophotometric and fluorometric techniques. From each site, one of the three replicates was analysed on a spectrophotometer following a 24-hour cold ethanol (EtOH) extraction (Wintermans and De Mots 1965) using methods outlined by Bergmann and Peters (1980) and Webb et al. (1992). The remaining two replicates were analysed using a Turner 10AU fluorometer following a 7 minute digestion in 90% EtOH at 808C. "
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ABSTRACT: Beavers (Castor spp.) are ecosystem engineers and important modifiers of freshwater ecosystems. They create impoundments that flood the surrounding landscape and modify the flow of materials through streams, thus potentially increasing nutrients, productivity and the availability of toxic methyl mercury (MeHg) to downstream food webs. Here we quantify food web-available MeHg in water, periphyton, and invertebrates collected from 15 streams up- and down-stream from beaver impoundments in the Rocky Mountain foothills of Western Canada. While nutrients, algal biomass, and total invertebrate standing stock were not significantly elevated below ponds, MeHg concentrations (average increase of 1.73) and percent of total Hg that was MeHg (average increase of 1.33) showed a trend of higher values in all compartments downstream and the difference was significant in predatory invertebrates. This suggests that beaver impoundments can increase the availability and subsequent uptake of MeHg by basal food web organisms even if their immediate influence on nutrients and resources is limited. As beaver populations continue to rebound, more research is needed to fully characterise the effects of beavers on nutrient and contaminant cycling under different biogeochemical conditions.
Available from: Sobhy Derhab
- "Chlorophylls a and b were determined on red and green cheek according to ( Wintermans and Mat , 1965 ) as follows : half gram of fresh peel was extracted by about 15 ml of 85% acetone and 0 . 5 g calcium carbonate , the mixture was filtered through a piece of cotton by using a glass funnel and the residue was washed with a small volume of acetone and brought up to 25 ml . "
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ABSTRACT: Effects of preharvest sprayable 1-methylcyclopropene (1-MCP), ethephon and ProTone (contains abscisic acid) alone or in combination on preharvest abscission, fruit quality and storability were studied on "Anna" apples (Malus domestica Borkh.). During 2013 and 2014 seasons, "Anna" apple trees were sprayed at the mature green stage with 1-MCP at 1 mM (54.3 ppm) or 2 mM (108.6 ppm), then one week later, they were followed by either ethephon at 50 ppm or ProTone at 50 ppm, as well as sole application of ethephon at 50 ppm and ProTone at 50 ppm. Random samples were collected from each tree after one week of ethephon or ProTone containing treatments, and then divided to two groups, the first to monitor the changes in preharvest abscission, physical and chemical characteristics at harvest. Meanwhile, the second group fruits stored for 30 days at 2 oC in air (85-95% relative humidity). In contrast to either ethephon or ProTone as individual application, 1-MCP treatments caused a significant reduction in preharvest abscission percentage of "Anna" apples while maintaining fruit firmness. Meanwhile, a drastic increase in anthocyanin occurred at the red cheek with ethephon treatment alone or when followed the 1-MCP treatment by one week. Meanwhile, 1-MCP mitigated the adverse influence of either ethephon or ProTone on flesh firmness after 30 days of cold storage.
Available from: Thomas D. Sharkey
- "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). "
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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.
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