146 



BIOCHEMICAL SYSTEMATICS 



to have a restricted distribution taxonomically, sometimes in a sug- 

 gestive pattern (for example, gentiobiose is found among species of 

 the Rosaceae). More intensive investigation of the distribution of 

 specific disaccharides must occur before any evaluation of the sys- 

 tematic imphcations of their distributions can be made. The higher 

 ohgosaccharides are mostly products of partial hydrolysis of poly- 

 saccharides. However, several non-reducing ohgosaccharides are 

 known to occur in various parts of a number of different plant species. 

 The important non-reducing ohgosaccharides are rafiinose, planteose, 

 gentianose, stachyose, mehzitose, and verbascose. 



In general there is little data available on the systematic 

 imphcations of the distribution of ohgosaccharides. MacLeod and 

 McCorquodale (1958) compared water-soluble carbohydrates of the 

 Gramineae and evaluated these substances as phylogenetic criteria. 

 Ohgosaccharides were among the sugars identified. These authors 

 were primarily concerned with the tribal disposition of certain genera. 

 Twenty-two species, representing eleven tribes, were analysed. Since 

 all of the species contained glucose, fructose, and sucrose, only the 

 more complex sugars provided any useful information. The authors 

 arranged the genera into six groups based on the presence of certain 

 types of oligosaccharides (Table 8-2). 



Raffinose is a trisaccharide (galactose-glucose-fructose) while 

 stachyose, a tetrasaccharide, contains two galactose residues attached 

 to glucose of a glucose-fructose unit. This difference between the two 

 oligosaccharides may be regarded as minor. In fact, the authors note 

 that barley embryos infiltrated with concentrated raffinose solution 

 win form some stachyose though normally the sugar is absent. 



