Fatty acids, sterols and hydrocarbons in the leaves of mangroves from northern Australia and New Zealand

Full description

Fresh leaves were collected from 11 species of mangrove plants for lipid analyses. The species examined were Avicennia marina, Avicennia marina var resinifera, Xylocarpus granatum, Rhizophora stylosa, Rhizophora apiculata, Rhizophora mucronata, Ceriops tagal var. australis, Bruguiera sexangula, Bruguiera gymnorrhiza, Acanthus ilicifolius and Sonneralia caseolaris, which were cultivated from seedlings in a shadehouse at the Australian Institute of Marine Science (AIMS). Ten of these species can be found along the coast of north Queensland, while Avicennia marina var resinifera occurs in New Zealand.The leaves were cut into small pieces and ground in an agate mortar and pestle under CHCl3-MeOH (1:1). After extraction, an aliquot of the solvent extract was saponified and partitioned to give the neutral lipids and the acidic lipids. Sterols and hydrocarbons were isolated from the neutral fraction by normal-phase HPLC. The acidic lipids were methylated with H2SO4-MeOH and analysed by GC. The sterols were further treated and after extraction yielded the steryl methyl ethers, which were analysed by GC. The hydrocarbons were also analysed by GC. Moisture content was also determined on separate leaf samples.
This research was undertaken to assess the importance of mangrove leaves as a source of organic material such as fatty acids, sterols and hydrocarbons for food webs within coastal ecosystems. Variations in fatty acid, sterol and hydrocarbon composition were examined for potential chemotaxonomic significance.

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Statement: Statement: Sterols and hydrocarbons were isolated from the neutral fraction by normal-phase HPLC using a CN-bonded column [250 mm x 4.6 mm i.d., Spherisorb CN (5 µm)], under isocratic conditions with iso-octane-PrOH (99:1, 1.0ml/min) as eluant. UV absorbance was monitored at 210 nm.The acidic lipids were methylated with H2SO4-MeOH and analysed by GC using a fused silica WCOT SP2100 column (50 m x 0.2 mm i.d.) and a fused silica WCOT Superox 0.1 column (50 m x 0.2 mm i.d.). The columns were programmed from 150° to 270°C at 2°C/min.The acidic lipids were methylated with H2SO4-MeOH and analysed by GC. The sterols were treated with Mel-18-crown-6 ether-K tert-butoxide (in DMSO, 60°C, 15 min). Two extractions with iso-octane-CHCl; (4:1) yielded the steryl methyl ethers, which were analysed by GC using the SP2100 column with programming from 150° to 270°C at 10°C/min, followed by a 30 minute isothermal period at 270°C during which the methyl ethers eluted.The hydrocarbons were analysed using the SP2100 column, with programming from 150° to 270°C at 2°C/min. H2 was used as carrier gas (linear flow: 35 cm/sec). Eluting peaks were detected by FID, with injector and detector temperatures set at 280°C.Steryl methyl ethers were identified by comparison of chromatographic R,s with those of authentic standards and the results published in:Wannigama GP, Volkman JK, Gillan FT, Nichols PD and Johns RB (1981) Phytochemistry 20, 659.Authentic standards of sterols were provided courtesy of the Medical Research Council (UK).Hydrocarbon identifications were based upon comparisons of their ECL values with standards, where available.

Notes

Credit
Hogg, Ronald W, Mr (Principal Investigator)