] 30 BIOCHEMICAL SYSTEMATICS 



evolutionary development of plants, are by no means distinguished by 

 having the highest iodine values, as might be expected if it is thought 

 that the degree of unsaturation increases during evolution. 



Another problem which must be solved in the metaboKsm of 

 fatty acids is the enzymatic coupling of the acid to form an ester 

 linkage with glycerol. If this reaction is rather unspecific, then what 

 prevents the incorporation of shorter chain "intermediates" into 

 triglycerides? A related question is that of the mechanism for ter- 

 minating the extension of the carbon chain. One reaction has been 

 reported which provides a partial answer to both questions. This re- 

 action involves the acyl attachment from an acyl CoA group to 

 phosphoglyceric acid with the liberation of CoA. The reaction 

 proceeds more efficiently with sixteen- and eighteen-carbon acyl CoA 

 compounds and is probably an intermediate in phosphatide (for ex- 

 ample, lecithin) synthesis. In any case, it is clear that the presence of 

 such enzymes could result in the capture of fatty acids of appropriate 

 chain length as they are synthesized. Frequently, it appears that a 

 given species tends to synthesize saturated fatty acids possessing two- 

 carbon atoms more or less than that of the major component (Hil- 

 ditch, 1952), again suggesting the possibility of less than absolute 

 specificity for certain enzymes governing fatty acid synthesis. Perhaps 

 this area would be particularly fruitful for comparative enzyme 

 studies-both from the standpoint of their catalytic properties and 

 their absolute chemical constitution (that is, amino acid sequence). 



It is evident from the review by Meara (1958) that, except for 

 the seed fats, relatively little systematic significance can be gleaned 

 from analysis of plant fats. For example, fats of roots usually rep- 

 resent minor components. In a few cases, notably the sedge Cyperus 

 esculentus, the oil content may be high. The fat content of bark is 

 usually on the order of 3 per cent and in the few species examined the 

 major fatty acid was the common oleic acid. More frequently, fruit 

 coat fats may acquire a relatively high concentration of oil. Yet, ac- 

 cording to Meara, "the characteristics and component fatty acids of 

 most of the fruit coat fats, irrespective of their botanical family, are 

 very similar." 



It has generally been believed that leaf lipids and the con- 

 stituents of leaf surface waxes are rather similar among different plants 

 (Hilditch, 1956). However, since the advent of chromatographic tech- 

 niques including gas chromatography, much evidence has been ac- 

 quired indicating that the leaf waxes contain a quite diverse 

 assemblage of hydrocarbons of different lengths including branched 

 chains, alcohols, aldehydes, ketones, acids and esters. Even a new 



