The Relationship between Metabolism and the ‘Exchangeability’ of Ions in Plant Tissues2

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Abstract
The uptake of the rubidium ion by well-washed disks of carrot parenchyma has been determined at 0·2° C and 25° C., in the presence and absence of 10−4M. dinitrophenol, from solutions of rubidium chloride containing 0·5 and 5·0 meq./l. Readily-exchangeable and non-exchangeable fractions were separately indentified. The lowering of temperature and application of DNP reduced the magnitude of both ion fractions at each of the two concentrations of rubidium chloride. Despite the fact that the uptake of ions into an exchangeable form at 5·0 meq./l. was about 3 times greater, the combined effect of low temperature and the presence of DNP reduced this fraction by a relatively constant absolute amount. Under the same conditions the uptake of ions into a non-exchangeable form from each concentration was reduced by approximately the same percentage. Over a 6-hour period the rate of uptake of rubidium into a non-exchangeable form at 25° C. was relatively constant, whereas at 0·2° C. there was an initial rapid uptake lasting for about 60 minutes followed by a slow steady uptake. The Q10 of this latter process measured after 360 minutes was 2·3. It is concluded that an appreciable part of the capacity of the tissue to hold ions by exchange is dependent on concurrent metabolism. The significance of measurements of exchangeability in the interpretation of mechanisms of ion uptake is discussed.

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