Studies in the Metabolism of Crassulacean Plants; The Effect upon the Composition of Bryophyllum calycinum of the Form in which Nitrogen is Supplied

Abstract

It has long been known that B. calycinum exhibits a pronounced diurnal variation in composition with respect to organic acids, the leaves becoming enriched, particularly in malic acid, during the night but undergoing marked loss of acidity during the day. Furthermore, culture of plants in general upon nitrate-containing solns. has been observed to lead to increase in the content of organic acids as compared to the effect of culture on solns. that provide N in the form of NH4 ions. In view of these facts, analyses have been carried out of the leaf and stem tissues of B. calycinum collected in the morning at a time of relatively high acidity, from plants cultured on a series of solns. in which a constant cone, of N was furnished. Composition of the culture solns. was varied in steps in the relative proportions with which nitrate ion and ammonium ion were supplied. The extremes were solns. that provided all nitrate ion and all ammonium ion. Results are presented as curves in which composition is plotted against the percent -age of ammonium ion in the culture soln. The curves show composition in terms of gms. per plant (absolute quantity) and gms. per kilo of tissue (cone). In the leaves, the organic solids, water, total N, nitrate N, organic soluble N, total organic acids including isocitric, malic and citric acid, starch, crude fiber and fermentable carbohydrate diminished in absolute quantity per plant with increase in the proportion of ammonium ion in the culture soln. Protein N, ammonia N, and glutamine increased to a maximum and then decreased. Asparagine decreased and then increased. Un-fermentable carbohydrate increased. In the stems, most of the components followed a similar course except that the ammonia N and glutamine increased continuously. On a cone, basis, organic solids of the leaves, together with total N, starch, soluble carbohydrates, unfermentable carbohydrates and "sedoheptose" increased, the protein N and ammonia N increased to a maximum and then decreased, the asparagine and organic soluble N decreased to a minimum and then increased, while the water, nitrate N and total organic acids including malic, isocitric, and citric acids decreased. In the stems, the cone, of components followed a similar course except that nitrate N decreased profoundly while ammonia N, glutamine, and organic soluble N increased throughout. B. calycinum follows the general rule that Organic acidity of tissue is diminished by culture on NH4 ion as the source of N. The change falls upon both malic and isocitric acids and affects the quantity of each of these substances present in the leaves equally. Citric acid is affected to a smaller extent with respect to quantity, but the proportional change is even greater.