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BIOCHEMICAL SYSTEMATICS 



(de Roubaix and Lazer, 1960), and these may also be self-inhibitors in 

 the seeds and fruits in which they occur. There are also numerous 

 scattered reports of phenohc inhibitors of certain fungi and plant 

 viruses (Uritani, 1961). 



Although the amino acids tyrosine and dihydroxyphenyl- 

 alanine, certain alkaloids, and other substances are phenolic in nature, 

 customarily the term, phenohc compound, is not extended to include 

 nitrogenous derivatives. Also, certain phenols are demonstrably 

 related to a parent substance belonging to a different chemical group, 

 for example terpenes, as in the case of thymol. Major categories 

 of phenolic substances include the following: simple phenols without 

 side chains; simple phenols with one, two, or three-carbon side 

 chains (occurring as acids, aldehydes, ketones, or alcohols); depsides 

 of simple phenols (for example chlorogenic acids: see Fig. 11-1); 

 and higher polymers of simple phenols such as the important 

 structural component of vascular plants, lignin. Another large and 

 important group of phenolic substances is the flavonoids, which in- 

 clude the vacuolar pigments such as the anthocyanins and antho- 

 xanthins, in addition to other classes. Finally, coumarins, which are 

 unsaturated lactone derivatives (for example, coumarin and scopoletin), 

 and which may be derived from the same biosynthetic pathway as that 

 leadmg to simple phenohc compounds, are also included with the 

 phenohc compounds. Phenohcs are usually present in the plant as 

 glycosides or esters. 



Certain of the phenohcs have been the objects of a large num- 

 ber of productive biochemical genetic studies, and also recently there 

 have been important new advances in knowledge of the biosynthesis 

 of these compounds. Knowledge of the genetics and biosynthesis of 

 phenols should contribute to a clearer understanding of the meaning 

 of some of the results of biochemical systematics studies. For this 

 reason, brief discussions of the mode of biosynthesis and certain as- 

 pects of the genetics of flavonoids are included in this chapter. 



Present knowledge of the comparative biochemistry of sec- 

 ondary compounds and particularly their mode of inheritance is often 

 inadequate to provide much important insight into their systematic 

 significance in a given instance beyond strict correlations of systematic 

 distribution. Consequently, many biochemical systematic studies rep- 

 resent a rather empu-ical search for patterns of distribution of partic- 

 ular substances or groups of substances. It should be recognized, 

 however, that for the vast majority of morphological characters used 

 as systematic criteria, the genetic mechanisms responsible for the 

 characters have not been revealed either. Therefore, in those cases 



