The Balance Sheet of Metabolites For Potato Discs Showing the Effect of Salts and Dissolved Oxygen on Metabolism At 23° C1

Abstract

The effects of 6 selected salt and O2 treatments during 70 hrs. at 23[degree] C on the respiration and metabolism of potato discs were investigated. Those salt treatments (KN03, Ca(Br)2) in which uptake of the anion exceeded that of cation caused an increase in the bicarbonate conc. and alkalinity of the external soln. In aerated solns. K salts stimulated, and Ca salts depressed, water absorption in a manner not wholly explicable by osmotic phenomena. At O2 tensions such that respiration was not limited by O2 the respiratory behavior of potato discs was governed by the salts in the external soln. When the conc. of KBr in the external soln. was increased, the respiration rate also increased. In the presence of Ca(Br)2 the respiration was less than in distilled water. At the same equivalent conc. KN03 increased respiration more than did KBr. The effect of low O2 concs. on respiration was confirmed. All the treatments caused an increased sugar conc. relative to that in the initial tissue. The salt and O2 treatments which stimulated respiration produced a low, residual sugar cone. The conc. of sugar did not regulate the respiration rate. At a low O2 conc. (soln. in equilibrium with 3.8% O2) at which accumulation of Br- was depressed, synthesis of protein from amino acid was also limited by O2 lack. In aerated distilled water protein synthesis occurred and this was increased by the presence in the external soln. of KBr but decreased by CaBr2. Dilute KN03 produced the greatest effect on protein synthesis. An approx. linear relationship was found between the amt. of protein synthesized and the quantity of CO2 respired. Approx. 1/3 of the respiration of discs in aerated distilled water was produced independently of N metabolism. This component of the total respiration was not affected by salts or O2 conc. 2/3 of the respiration of discs in dist. water arose from a component of respiration which is linked to protein synthesis from amino acids, is affected by salts and O2 conc. and in which the oxidase system is involved. The effects of inorganic ions on respiration were parallel to their effect on protein synthesis. K+ and NO3 intensified, Ca++ retarded, the effect of O2 on respiration. The characteristic effects of ions on respiration and synthesis were exerted at O2 tensions at which their absorption occurs and the reactions of the ions observed therefore constitute an integral part of the machinery of salt absorption. Volatile organic compounds were produced by potato tissue only in small amt. Such compounds appeared in the flowing gas stream and small amts. were evolved when the tissue is dried. The carbon value of the total production of volatile compounds was of the order of 7.5% of the total respiration.-A revised balance sheet embodies corrections for all the above processes and summarizes the principal processes which occur in potato discs under the conditions conducive to salt uptake and the effects of salts and O2 upon them at 23[degree] C. The amino acids and sugar supply the C for the protein molecule and the extra respiration entailed in its production. In the fixation of nitrate N, C is derived from other sources (organic acids). Organic-acids disappear during protein synthesis from amino acids and probably contribute here also to the C framework of the protein molecule.