1919] 



MCGINTY— DIASTASE ACTIVITY OF SOLANUM TUBEROSUM 235 



The author states, finally, that since the distribution of sugar in 

 resting and germinating potatoes is not essentially different, its 

 appearance in quantity at the time of germination should be 

 ascribed, partly at least, to metabolic changes induced by other 

 agencies. 



Doby and Bodnar ('15) investigated diastatic activity in 

 tubers from healthy potato plants as compared with that in 

 tubers from plants affected with leaf roll. They found the 

 absolute value of the diastase (diastase plus zymogen) to be 

 the same in healthy and diseased potatoes, but, in general, more 

 zymogen was found present in healthy than in diseased tubers. 

 These workers also investigated the presence of zymogen in the 

 extracted juice of potatoes. They observed that the diastatic 

 activity of the juice increased upon standing, which fact they 

 attribute to the rapid conversion, in the extracted juice, of 

 zymogen into amylase. Fresh juice, which was quite active 

 to begin with, did not increase to the same extent as did other 

 juice in which diastase was less active in the beginning. Less 

 zymogen was found to be present in tubers in the middle of the 

 rest period than at other times. It began to increase during 

 the first half of January, and a corresponding increase in dia- 

 static activity was observed at the same time. In the spring 

 only small amounts of zymogen were found, since at that time 

 most of it had been changed into active diastase. 



It was believed by these investigators that the diastatic 

 activity of fresh juice depends chiefly upon the stage of develop- 

 ment of the tuber, but that it may also be affected by the kind 

 of potato used and by climatic and cultural conditions during 

 growth. The stage of the rest period must also be taken into 

 consideration when determinations are made during that time. 

 Enzyme activity was found to be almost entirely independent 

 of the size of the tubers. This calls attention to the necessity 

 for the consideration of these factors in relative diastatic activity 

 determinations, and emphasizes the importance of a uniform 

 procedure as regards the time that elapses between the different 

 operations necessary in such determinations, as well as the 

 importance of using material, the different stages of which have 

 developed under known and comparable conditions. 



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