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PLANT BIOCHEMISTRY 



Alkaloids 



Many plants throughout the world accumulate organic nitrogen 

 bases called alkaloids. Although a large number of medicinally im- 

 portant alkaloids have been isolated, only in nicotine, nornicotine, and 

 anabasine of tobacco has the plant physiology been studied extensively. 

 Nicotine is the principal alkaloid of tobacco and constitutes 0.5 to 8 

 per cent or more of the dry leaf. The quantity found in tobacco is a 

 function of variety and type, nutritional status, and growing condi- 

 tions. Nicotine is synthesized predominantly in the roots and trans- 



ported upward in the transpiration stem to the leaves. Many workers 

 believe that nicotine, once formed and transported to the leaf, under- 

 goes no further change and remains outside the metabolic pool. Re- 

 cent work with C^^- and N^Mabeled nicotine has indicated that this 

 is not entirely true. The tracer element was found in the amino acids 

 and other nitrogenous constituents in plants supplied with tagged 

 nicotine. 



Nicotine is converted to nornicotine in the leaf of tobacco. In most 

 varieties and types only a small portion of the nicotine is converted to 

 nornicotine, but in a few selected varieties nornicotine predominates. 



Anabasine is found in small to negligible quantities in most tobac- 

 cos of commerce, although it is the principal alkaloid of the tobacco 

 species Nicotiana glaiica. Unlike nicotine, this alkaloid is produced 

 in both the roots and the leaves. 



The solanaceous plants produce a number of alkaloids of medicinal 

 value. Atropine, a drug used to dilate the pupil of the eye, is produced 

 by a number of plants of the belladonna family. Most of the drug is 



HoC 



