INFIvUENCE OF THE SUBSTRATE AND ITS HYDROGEN- 
ION CONCENTRATION ON PECTINASE PRODUCTION ' 
By L. ly. Harter and J. L. Weimer, Pathologists, Office of Cotton, Truck, and Forage 
Crop Disease Investigations, Bureau of Plant Industry, United States Department of 
Agriculture 
INTRODUCTION 
Former investigations by the authors (9)^ have shown that Rhizopus 
tritici Saito produces a substance of the nature of an enzym which has 
the power to dissolve the middle lamellae of raw sweet-potato {Ipomoea 
batatas) disks. This macerating principle was found to be thermolabile 
and to be produced abundantly in sweet-potato decoction in cultures 
one or two days old. It was found that while the mycelium itself retained 
some of the enzym which is called pectinase in these investigations, a 
portion of it was excreted into the culture solution on which it grew. 
Investigations have also proved that pectinase is produced by a number 
of other species of Rhizopus, some of which are able to cause a typical 
softrot of sweet potatoes. The amount of enzym produced was not 
equal in all cases. The most parasitic species did not necessarily produce 
the largest amount of enz)mi under cultural conditions. For example, 
Rhizopus nigricans Ehrb., which is the common softrot-producing 
organism in sweet-potato storage houses, produced a small amount of 
enz5mi in culture. 
In order to study the action of the enzym on raw sweet-potato disks, 
the organism was grown for two or three days in a solution of sweet- 
potato decoction. The mycelium was then removed and treated accord¬ 
ing to a method described elsewhere (9). The ability of the enzym, 
contained both in the mycelium and in the solution, to macerate raw 
disks was tested. Measured portions of the solution were pipetted into 
small flasks, some of which were steamed to inactivate the enzym. 
Raw sweet-potato disks i cm. in diameter and i mm. in thickness were 
dropped into the steamed and unsteamed solutions which were then held 
at 45° C. Maceration was usually completed in from 2 to 4 hours in the 
solution containing the active enzym. The disks in the steamed controls 
had not been acted upon in that Ijength of time. If, however, the disks 
in the control solutions were examined at the end of 24 hours, they were 
frequently found partially or completely macerated, the cells separating 
along the line of the middle lamellae in a manner typical of those in 
active enzym solution. In searching for an answer to this curious 
phenomenon two possible explanations presented themselves; first, that 
the enzym was not actually completely inactivated, although the solu¬ 
tions were steamed in an Arnold sterilizer for 10 minutes; second, that 
some other substance was produced which acted in a manner identical 
with the enzym itself. 
When a modified Czapek’s nutrient solution was used, a solution 
employed quite generally in these investigations, the results were even 
* Accepted for publication Jan. 22, 1923. 
2 Reference is made by number (italic) to “ Literature cited,” p. 877-878, 
Journal of Agricultural Research 
Washington, D. C, 
aeu 
Vol. XXIV. No. JO 
June 9. 1923 
Key No. G-310 
(861) 
