330 



BIOCHEMICAL SYSTEMATICS 



to loss while non-volatile constituents may often be light-sensitive or 

 else subject to autocatalysis. It is possible that plant material which 

 remains alive for a long period of time following collection will 

 not only undergo degradative changes but may even synthesize com- 

 pounds not normally produced. Also, if material remains moist after 

 collection, invasion by molds and other microorganisms may occur. In 

 our own work with Baptisia we have observed that plants which are 

 carefully pressed and dried at 40 to 50° C then stored in a cool, dark 

 (herbarium) cabinet apparently undergo few significant post-harvest 

 changes. Alston and Irwin (1961) compared various drying schedules 

 for the preservation of ninhydrin-positive and fluorescent compounds 

 of Cassia species. They found that combinations of temperatures be- 

 tween 30° and 50° C and of drying periods between nine and forty 

 hours yielded extracts with quite similar ninhydrin and fluorescent 

 patterns. When some of the same Cassia material stored in darkness 

 at room temperature for seven months was re-extracted, the patterns 

 were basically unchanged. These observations need to be confirmed 

 by more rigorous controls, but if the type of preservation suggested is 

 found to be adequate, then plant collections such as are made for the 

 herbarium with essentially routine collecting procedure should be 

 suitable for limited biochemical studies. 



Chromatography itself may produce certain artifacts. Har- 

 borne and Sheratt (1957) found that the pentose, arabinose, occurred 

 as an artifact in the purification of anthocyanins if solvent mixtures 

 containing HCl were used. This type of artifact is quite troublesome 

 if one is investigating anthocyanins, for the positions and types of 

 glycosides represent a major portion of the problem of identification. 

 Of course, it is important to reduce the danger of partial or undesired 

 hydrolysis by giving special attention to conditions during the extrac- 

 tion of various substances. 



In addition to paper chromatography, gas chromatography 

 can be utiHzed to advantage in biochemical systematic investigations, 

 although it is still employed in highly speciahzed problems. Gas 

 chromatography can be quite effective, requiring even less of a 

 sample than does paper chromatography— in fact with high sensitivity 

 detectors one may "see" one part per bilhon. Compounds which can 

 be volatilized without degradation at temperatures up to 600° C can 

 be chromatographed, and if the original substance is not volatile, it 

 may be converted to a derivative that is volatile in the desired range 

 (for example, methyl esters of fatty acids). In the hands of experienced 

 technicians gas chromatograms may give striking results (Fig. 16-2). 



It is possible that one contribution of gas chromatography to 

 biochemical systematics will be through the use of "fingerprint" 



