STUDIES IN THE METABOLISM OF CRASSULACEAN PLANTS: THE EFFECT OF TEMPERATURE UPON THE CULTURE OF EXCISED LEAVES OF <i>BRYOPHYLLUM CALYCINUM</i>

Abstract

When Bryophyllum calycinum leaves are detached from the plant and cultured in water in darkness at ordinary room temperature, the course of the changes in composition with respect to the organic acids, the protein and the starch depends upon the time of day at which the samples were collected (5). If leaves are taken in the afternoon at a time of low acidity and low protein content, there is a prompt increase both in acids and in protein and a corresponding decrease in the high starch content. Alternatively, if the leaves are collected in the morning at a time of high acidity and protein content, both acids and protein fall and the starch increases. These changes take place within the first 24 hours and appear to be expressions of the normal metabolism of this species. After 24 hours, certain other changes begin to make their appearance ; in particular, for leaves collected in the afternoon, the acids and the protein, after reaching maxima, begin to fall and the starch may increase during the second day of the culture period. It seems possible that this reversal in the direction of the chemical changes represents the initiation of the catabolic changes that inevitably follow excision of a leaf. Accordingly, in order to study this possibility further, an experiment was carried out in which the culture period at 20? C. was prolonged to 6 days and, in addition, parallel cultures were carried out at 9? C. and at Io C. in the hope that, at the lower temperatures, the reactions might proceed more slowly and certain of the details might be revealed more clearly. The present paper gives a report of this experiment.