Studies in the Metabolism of Crassulacean Plants: Changes in the Composition of Bryophyllum calycinum During Growth

Publisher Website
Google Scholar
Abstract
The composition of the leaf and stem tissue of B. calycinum plants, harvested at noon on sunny days at intervals over a period of 95 days, was detd. to obtain fundamental data upon the rate of growth of a plant which is characterized by a pronounced diurnal variation in organic acid content. The composition is recorded in terms of gms. per plant. The rate of accumulation of the fresh wt. and of many of the components, in particular the organic solids, the ash, the water, the protein, the nitrate N, the soluble carbo-hydrates, the crude fiber (cellulose), the total organic acids, and the malic acid followed essentially straight line curves throughout the periods of observation. The total N followed a curve somewhat concave to the time axis, as was true also of the isocitric acid and citric acid, suggesting a gradual slowing of the rate of accumulation of these components. The starch of the leaves, by far the most plentiful known component of this tissue, followed a curve markedly convex to the time axis, indicating an increase in relative capacity for the storage of starch as the leaves matured. The data were also computed in conc. units, namely in grams per kilo of fresh wt. of the tissues. These curves show a moderate degree of irregularity in the relative concs. of the various components at different stages of growth. Comparison of the data with similar results for the tobacco plant, at an analogous period in the life cycle, showed marked differences in the rate of accumulation of most of the components. The tobacco plant grows much faster as measured by almost all of the criteria. The most important exception is in the rate of accumulation of organic acidity; isocitric acid is formed almost as rapidly by the Bryophyllum plant as malic acid is by the tobacco plant, and citric acid is formed at almost equal rates in the 2 spp. On the other hand, oxalic acid, which is a major organic acid component of the tobacco plant, is present only in traces in Bryophyllum. Isocitric acid is the predominating organic acid component of Bryophyllum leaf tissue and is present in young leaves to the extent of about 18% of the organic solids; such tissue is accordingly valuable for the prepn. of this rare acid in quantity.