Investigation of Respiratory and Ion Transport Properties of Aging Bean Stem Slices

Abstract

Ion and oxygen uptake were studied on aging bean stem slices. Oxygen uptake was high immediately after slicing, decreased to a minimum at 100 minutes, and then increased again. Ion uptake per unit of 02 uptake data suggested that metabolic energy was utilized almost exclusively for sodium transport in fresh tissue but was diverted to potassium transport as the slices aged. Oxygen and ion uptake in fresh slices was less sensitive to 2, 4-dinitrophenol as compared to the aged slices, indicating major metabolic and physiological changes occurred during aging. This was further substantiated by the tissue response to cyanide and antimycin A. Oxygen uptake was decreased by cyanide (22% by 1 mM) and antimycin A (14% by 1 microgram per milliliter) in fresh slices but not in aged slices. Potassium uptake that developed during aging was sensitive to cyanide and antimycin A. The results are pertinent to understanding the role of the stem in regulating ion transport in plants.The ionic environment of plant leaf cells is a result of the operation of several ion transport systems. The stem has recently been recognized as an important system in regulating ion flow to the leaves. Jacoby (6), utilizing brittle wax beans, has presented cogent experiments. When derooted bean plants were placed in low concentrations of NaCl, Na' was retained in the basal portion of the stem, whereas Cl was distributed throughout the entire plant. Sodium concentration was highest in the lower portion of the stem and decreased exponentially with distance from the base. Sodium retention in the stem was sensitive to metabolic inhibitors, and it was concluded that Na retention in the basal parts was due to its active accumulation by cells lining the translocation path (7).Observations on the ion uptake characteristics of bean stem slices have yielded more information on the nature of the ion absorption system in the stem. Rains (16), investigating the ion uptake properties of brittle wax bean slices, observed that Na uptake was much greater than K uptake in freshly sliced stem tissue.