THE SECRETION OF INVERTASE BY PLANT ROOTS 
Lewis Knudson 
In an earlier paper (Knudson, 3) on the utilization of certain carbohy- 
drates by green plants, the observation was repeatedly made that reducing 
sugars appeared in culture solutio,ns containing sucrose. In discussing 
the possibility of invertase secretion the following statements were made: 
"It has not yet been definitely proved that the inversion of saccharose is due to inver- 
tase secreted into the culture solution. It is possible that the saccharose is inverted in the 
roots and the reducing sugars are secreted, but this is less probable. It is possible also 
that the enzyme may be released as a result of the death of root hairs or other cells of the 
root and that it is not secreted from living cells." 
A few observations have been made by other investigators on this 
subject of enzyme secretion, but the observations have been only incidental 
to other investigations and the few reports are conflicting. It seemed 
desirable therefore to investigate thoroughly the possibility of enzyme 
secretion and particularly that of invertase, since it is this enzyme that is 
most likely to be found in the roots of plants. Accordingly the investi- 
gation here reported was undertaken. Not all the experiments performed 
are reported, but those omitted are in agreement with the results here 
given. 
Methods 
The methods employed are essentially the same as those used by Knud- 
son and Smith (4) in their experiments on the secretion of amylase. The 
plants were grown in water cultures under sterile conditions, that is, with 
the root system in a nutrient medium free of microorganisms and the seed 
removed from contact with the culture solutions. The type of culture is 
shown in figure i. The details of manipulation are sufficiently described 
by Knudson and Smith (4) and need no repetition here. 
Pfeffer's nutrient solution was used, with the substitution, however, of 
dibasic potassium phosphate for the monobasic potassium phosphate. 
The solution was prepared according to the following formula: Ca(N03)2 
4 grams, K2HPO4 i gram, KNO3 i gram, MgS04-7H20 i gram, KCl 0.5 
gram, FeCls 50 milligrams, distilled water 6 liters. To this solution was 
added, when desired, sucrose. 
In the use of Pfeffer's solution, according to the formula given, it is 
essential that precautions be taken to prevent acidification of the culture 
solution. When the nutrient solution is sterilized in an autoclave for a 
period of 30 minutes or more, there may result an acid solution. This 
appears to be due to the reaction between calcium nitrate and dibasic potas- 
sium phosphate, whereby there is produced some tri-calcium phosphate 
371 
