Studies in the Metabolism of Crassulacean Plants: The Behavior of Excised Leaves of Bryophyllum calycinum During Culture in Water

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Abstract
Equal samples of leaflets excised from B. calycinum plants were subjected to culture with the base of each leaflet immersed in water, one set of samples taken in the late afternoon being treated in the greenhouse and a second set in a completely dark room. A 3d set collected early in the morning was likewise placed in the dark room. Analytical data were computed in terms of 1 kg. of fresh tissue weighed at the time of sampling. There were no significant effects in any case upon the quantity of organic solids nor upon the ash, the alkalinity of the ash, or the total N; even the soluble carbohydrates failed to change. The samples cultured in the greenhouse increased sharply in organic acids during the night and decreased during the day, the greater part of the change being due to malic acid with citric acid playing a smaller but similar role. Isocitric acid decreased at night and increased during the day. Starch varied in a manner the converse of organic acids, the fluctuations being in each case through a wider range than those of the acids. Thus it is possible that organic acids synthesized at night arose from oxidation of carbohydrates. However, some source of starch other than the organic acids must be invoked to account for the starch synthesized during the day, yet the failure of the organic solids to increase significantly indicates that photosynthesis played only a small part. The leaves cultured in darkness starting in the afternoon at low acidity increased in malic, citric, and isocitric acids for 14 hours. The increase in malic and citric acids continued for the rest of the 1st day but isocitric acid then began to decrease. All three acids decreased during the second day. Starch decreased during the 1st day in darkness but increased significantly during the 2d. The leaves cultured in darkness starting in the morning at high acidity began to lose isocitric acid at once. Malic acid dropped slightly but citric acid increased; later malic acid dropped sharply, isocitric acid increased and citric acid remained constant. During the 2d day, isocitric acid and malic acid decreased, and citric acid remained unchanged. Starch increased slowly but continuously throughout the 2-day period in darkness. The changes in organic acids and starch can be largely accounted for if it is assumed that the several substances are linked by enzymatic reactions in a system analogous to the Krebs tricarboxylic acid cycle.

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