THE NATURE OF THE AUXIN‐INDUCED WATER UPTAKE BY POTATO TISSUE. II. THE RELATION BETWEEN RESPIRATION AND WATER ABSORPTION

Abstract

IT HAS BEEN shown by several workers that the absorption of water by potato discs is an aerobic process, and recently we have demonstrated that it can be inhibited by a variety of metabolic inhibitors (Hackett and Thimann, 1950). This process, furthermore, is promoted by indole-acetic and naphthaleneacetic acids and the resulting increase in water uptake can be blocked by the same inhibitors (Hackett and Thimann, 1952). The auxin-induced water uptake is not accompanied by -any increase, but by a definite decrease, in the osmotic pressure of the cell contents (Hackett, 1952). In order to gain some insight into the mechanisms of these effects, measurements of the respiratory rate (oxygen uptake) were made and the results are reported here. MATERIALS AND METHODS. The method used to prepare and maintain discs of potato tissue throughout the experimental period was described in detail in the previous paper (Hackett and Thimann, 1952). In essence, the discs were supported so as to break the surface of shallow layers of solution in Petri dishes, and the water uptake was calculated from changes in fresh weight. Direct measurements of the oxygen uptake of the discs were made using standard, constant volume Warburg respirometers, according to the technique described by Umbreit et al. (1949). Groups of 10 discs, 9 mm. in diameter, were blotted and weighed fresh, then placed in the respirometer vessels containing 3.0 cc. of water; the center well contained 0.2 cc. of 20 per cent KOH. The vessels were attached to the manometers, placed in 25?C. bath, and shaken at a rate of 140 strokes per minute. After 15-30 min., the manometers were read at 15-min. intervals. The oxygen uptake is given as Qo2, the number of cubic mm. of oxygen absorbed per hour per gram of initial fresh weight. In correcting the flask constant for the volume of tissue, the storage tissue was assumed to have a specific gravity of 1.0. The discs in the Warburg vessels are submerged under water and consequently the conditions are not the same as in the Petri dishes. Since potato discs deteriorate after some hours under anaerobic conditions (Brauner et al., 1940), oxygen uptake was followed for not over 3 hr., and fresh discs were used for each series of measurements. That is, the oxygen (and water) uptake was determined