Respiration of barley plants III—Protein catabolism in starving leaves

Abstract

In an earlier paper (Yemm 1935) the results of analytical and gasometric experiments with starving barley leaves were described. These experiments indicated that the respiratory mechanism was considerably modified under conditions of extreme starvation: the rapid breakdown of carbohydrates, conspicuous at first, may play only a minor part in the later stages. It was suggested that protein catabolism is important in the respiration of highly starved and yellow leaves. The evidence for this conclusion was drawn primarily from observations of the respiratory quotient; such data are notoriously difficult to interpret and alone they do not lead to any satisfactory certainty. In the present case further information could be gained by biochemical examination of the transformation of proteins and other nitrogenous compounds occurring during progressive starvation. By this means the preliminary analysis of the living system by gasometric methods could be extended. It is known that loss of protein occurs in plants under conditions of carbohydrate shortage. Onslow (1931) has collected together analytical data which show this in both etiolated seedlings and isolated organs, while the researches of Chibnall (1922a, 19246), Mothes (1926), and Vickery, Pucher, Wakeman and Leavenworth (1933) have provided information especially for detached leaves. However, any detailed comparison of the results available with the starving barley leaves is obviously hazardous, since differences, both of the leaf type and of starvation conditions, may lead to confusion. Therefore, biochemical data have been sought for barley leaves starved under the controlled conditions previously used: a description of the analytical methods and results is given in this paper.