166 



BIOCHEMICAL SYSTEMATICS 



Webb found that from 753 species in 110 families tested, 145 species 

 from forty-one families contained alkaloids. 



The distribution of alkaloids within the plant and in the ceU 

 has been discussed by James (1950). Usually, the alkaloids, which are 

 water soluble, accumulate in the vacuoles and are rarely found in 

 dead tissues (even the quinine of Cinchona bark is said to be confined 

 to living cells). Alkaloids may be present in any part of a particular 

 plant and very often occur in meristematic tissue. In Baptisia leuco- 

 phaea, alkaloids have been found to be present in roots, stems, leaves, 

 flowers, fruits, and seeds, the highest concentration occurring in the 

 seeds. The absolute amounts and relative concentrations of the 

 various alkaloids in B. leucophaea differ from one part of the plant 

 to another (Brehm, 1962). 



Synthesis of alkaloids exhibits a number of interesting varia- 

 tions. For example, nicotine synthesis in Nicotiana is initiated in the 

 root and completed in the leaves. The lupine alkaloids, however, are 

 produced in rapidly growing shoots. Doubtlessly, many variations are 

 to be expected in the pattern of synthesis of such a heterogeneous 

 group of substances. 



Concerning the stability of alkaloids, James ( 1953) has said that 



... a given species always forms the same group of related alkaloids, 

 in more or less fixed proportions and within fairly narrow limits of con- 

 centration. It has proved very difficult to modify these relations, even 

 quantitatively, by simple experimental means. 



Mothes (1955) and other workers, however, suggest that 

 alkaloids are definitely affected by various external factors. In our 

 analyses of individual plants of Baptisia leucophaea from several 

 populations we have found a wide range in the absolute and relative 

 concentrations of the leaf alkaloids (Fig. 9-1). We do not know yet 

 whether or not these differences are genetic. However, even if the dif- 

 ferences were assumed to be genetic in origin, such extensive variation 

 would suggest a multiple gene system expressing the effects indirectly. 

 In such circumstance (for example, wherein alkaloid synthesis is 

 influenced by diverse internal factors) it seems likely that certain exter- 

 nal factors would also exert some influence. A relatively small propor- 

 tion of alkaloids has been studied with respect to questions of varia- 

 tion under experimental conditions. It is likely that the role of some 

 alkaloids in the plant is not critical, the factor of natural selection is 

 correspondingly presumed to be low, and therefore regulatory mecha- 

 nisms controlhng their synthesis would not be expected to be highly 

 refined. Furthermore, alkaloid synthesis is somewhat closely connected 



