EFFECTS OF pH AND THE COMPONENTS OF BICARBONATE AND PHOSPHATE BUFFERED SOLUTIONS ON THE METABOLISM OF POTATO DISCS AND THEIR ABILITY TO ABSORB IONS

Abstract

This paper consists of two parts. The first concerns the effect of certain variables on the absorption of bromide by potato discs and experiments which were made by the senior author in the Division of Plant Nutrition, University of California, in 1933-1934. The second part describes the effect of similar treatments on the metabolism of potato discs and experiments carried out with the assistance of the junior author at Birkbeck College, London, in 1937-1938. Since the results of the later work are essential for a full interpretation of that which preceded it, the two investigations are described together. Investigation of the effects of external pH presents an obvious approach to the problem of salt accumulation. It is, therefore, an essential part of any survey of the variables which affect this important process (18, 19, 20). Despite the great emphasis which others have placed upon the r?le of pH in salt absorption, detailed discussion of the effect of this variable on bromide absorption by potato discs has been long postponed. For some preliminary observations see (18). This delay was due to the knowledge that until the effects of a wide range of variables?including the nature and concentration of neutral salts?upon the behavior of cells had been investigated, phenomena due to hydrogen ion per se could not be segregated from those due to other variable components of the system used to control pH. Knowledge of the metabolic processes of potato tissue and the way these are affected by neutral salts (21, 22, 23) is now adequate to permit investigation of the problem. Of the buffer systems which can be used to regulate the pH of solutions in contact with plant cells, that which depends upon the proportion of bicarbonate to free carbonic acid is of outstanding interest since its components are metabolic products of cells. This paper contains a survey of the effects of pH, carbon dioxide, and potassium carbonate concentration. Though somewhat incomplete, it enables us to visualize the trend of the effect of these variables upon absorption and metabolism of potato discs and prepares 1 This paper is the fourth of a series of papers on the biochemistry of salt absorption by plants. The writers are indebted to Prof, D. K. Hoagland for proofreading this paper.