ACIDIFICATION OF UNBUFFERED SALT SOLUTIONS BY PLANT TISSUE, IN RELATION TO THE QUESTION OF TISSUE ISOELECTRIC POINTS

Abstract

In all cases observed by us, when plant tissue is placed in contact with a tenth-normal solution of calcium chlorid solution soon becomes acidified. Within an hour, under suitable experimental conditions, hydrogen-ion concentration may increase ten, twenty, or thirty fold. What is cause of this development of acidity? Should this effect be interpreted as evidence that tissue is absorbing cations faster than anions? And if so, is process of ion absorption related to amphoteric character of proteins in plant? This problem is important because it is related to question of whether plant tissue in absorption of ions behaves like an ampholyte with an isoelectric point. Through this connection we first became interested in it. The effect of seeds upon hydrogen-ion concentration of salt solutions was studied in detail by Rudolphs (6, 7, 8), who soaked seeds of different species in various salt solutions of different concentrations, and then determined pH of solution surrounding seeds. He was impressed by tendency of seeds to bring pH of various salt solutions to definite values, each final value being fairly constant for a given species of seed regardless of original pH or concentration of salt solution (except in case of very dilute solutions). Thus final value for corn (Zea mays) was between pH 3.9 and 4.2 when seeds were soaked in such varied chemical solutions as K2SO4, KNO3, CaC12, H2SO4, HCI, KC1, BaCl2, oxalic acid, citric acid, etc. Rudolphs' conclusion was that the chemical properties of chief protein constituent of seeds seem responsible for changes in hydrogen-ion concentration. Scott (g) found that mycelium of Fusarium lycopersici was able to change reaction of several different dilute salt solutions to pH 5.4 which was regarded as isoelectric point of tissue. Thus, behavior of living mycelium was thought to be analogous to that of an amphoteric colloid. We have experimented upon effect of plant tissue upon pH of unbuffered salt solutions, using 6 different tissues, I5 different salt solutions, with 3 to 5 different concentrations of each salt. In our experiments we