Polysaccharide Composition of Leaves
PLUM leaves (Prunus domestica) contain sufficient amounts of starch, cellulose, hemicellulose, and pectic substances to recommend them for studies of the biosynthesis and possible inter-relationships of these leaf polysaccharides and their monosaccharide precursors1. Experiments involving photosynthesis by plum leaves in carbon dioxide labelled with carbon-14 and subsequent fractionation of the leaf polysaccharides revealed marked differences, both in the extent to which carbon-14 was incorporated into the different monosaccharides of each fraction, and also in the specific activities of each monosaccharide from different fractions2,3. Further investigations could be facilitated by using leaves relatively richer than plum leaves in any one polysaccharide constituent. There is little information on this point, consequently a diversity of leaves has been examined for polysaccharides (Table 1).
Incorporation of Carbon-14 into the Complex Polysaccharides of Plants
THE carbon-14 tracer technique would appear to offer a unique opportunity for investigations of the biosynthesis and subsequent metabolism of pectins and hemicelluloses, provided that there is a measurable synthesis and turnover of these polysaccharides in plant tissues. After allowing four mature fruiting spurs, each with four to six leaves and two fruits, detached from plum trees (variety Victoria), to photosynthesize1 in the presence of carbon-14 dioxide (from 43.5 µc. barium carbonate-14C), the leaf polysaccharides and the water-soluble polysaccharides of the fruit mesocarp were isolated. Labelling of all the monosaccharide constituents was observed by hydrolysing the polysaccharides (N sulphuric acid ; 100° 16 hr.), separating the products on paper chromatograms and examining with a Geiger counter those areas containing the separated sugars. The specific activities of the latter were determined, after elution from the paper chromatograms, as infinitely thin films on planchets (see Table 1). The incorporation of carbon-14 into the fruit mesocarp polysaccharides may be due to photosynthesis by the fruit or by translocation from the leaves.
Comparative study of the molecular species of chloropropanediol diesters and triacylglycerols in milk fat
In an effort to establish the origin of the fatty acid esters of 3-chloropropanediol, which recently have been isolated in small amounts from goat milk, we compared the molecular species composition of the chlorohydrin diesters and of goat milk triacylglycerols. The chloropropanediol diesters were found to be composed of molecular species containing C10−C18 fatty acids and corresponded closely in carbon number to those calculated for the long chain sn-1,2-diacyl-glycerol moieties of goat milk triacylglycerols. The molecular species of goat milk total triacylglycerols contained C4−C18 fatty acids. It is suggested that triacylglycerols and chloropropanediol diesters are derived from the same pool of long chain fatty acids. A molecular distillate of bovine milk fat did not contain chloropropanediol diesters, while the available samples of human milk fat were shown to contain alkyldiacylglycerols as the major components of a neutral lipid fraction corresponding in polarity to the chloropropanediol diesters.