Chemical investigations of the rhubarb plant /

Abstract

source of the carbon compound with which the ammonia combines, although this is a matter of debate at the present time. This view of the function of the amides has been shown in this laboratory to agree in general with observations on the tobacco (85) and beet (81) plants. The German investigators, however, believe that in acid plants, particularly in Begonia., Oxalis, and Rheum species, ammonia is chiefly dealt with by direct neutralization by an organic acid. They quote experimental results that show concentrations of ammonia nitrogen in the rhubarb petiole far higher than are usually encountered in other species, and call attention to the parallel production of organic acids and ammonia during growth as an evidence of neutralization as the mechanism for deahng with these large amounts of ammonia. Whether or not rhubarb possesses an amide synthesizing mechanism of the usual type is left uncertain by their experiments, but Kultzscher (44) maintains that amide synthesis plays a very small part in acid plants and distinguishes between ammonium ions and free ammonia. He makes use of an idea that probably originated with Prianischnikow (64) according to which only free ammonia is thought to be toxic and, thus, in the acid plant where, at high hydrogen ion activities, the ammonia tension is reduced to infinitesimal proportions, there is no necessity for conversion into a neutral amide. These observations induced us to examine the organic acids of the rhubarb plant in some detail, and it was found that, in a series of samples of leaves collected at different times in the season, there was no evidence of correlation between the changes in the quantities of ammonia and of any of the three chief organic acids, /-malic, oxalic, and citric acids (66). Connecticut Experiment Station Bulletin 424 ured volume of water. The second lot of samples consisted of 10 leaves each and received the key letter E, to signify that the tissue was to be extracted with water. The management of this series of samples was the same as the D series. The material assembled for analysis at the end of the experiment consisted of the following: Fresh leaf control: Blade tissue and petiole tissue in duplicate from 20 leaves (FDl, FD2); dried. Blade tissue and petiole tissue extracts in duplicate from 10 leaves (FE1,FE2). Residues from extraction of blade tissue and petiole tissue, dried.

Loss of Ribulose 1,5-Diphosphate Carboxylase and Increase in Proteolytic Activity during Senescence of Detached Primary Barley Leaves

“…Other investigations have shown that light retarded losses of Chl (7) and soluble protein (7,38) in senescing tissue mainly by allowing photosynthesis (7). In the present study, light protected against a loss of soluble protein by greatly retarding the loss of RuDPCase protein (Table II).…”

Photosynthesis and Metabolism of Organic Acids in Higher Plants

“…This consistently high activity of malic acid confirms it as the key organic acid in the metabolism of many plants. The extensive studies of VICKERY, PUCHER, and coworkers (17,25,26) also have led to the conclusion that malic acid is metabolically most active of the organic acids normally analysed. Oxalic acid occupies the position of the least active acid.…”

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

“…2) but that the stems of even the oldest plants contained less than one-fifth as much organic acid as the leaves. This is the reverse of the situation observed in the rhubarb plant where the petiole was found to be far richer in organic acids (14) than the blade.…”