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Metabolism and Enzymology

Influence of Low Temperature on Respiration and Contents of Phosphorylated Intermediates in Darkened Barley Leaves ¹

Robert Hill Institute, University of Sheffield, Sheffield, S10 2TN, United Kingdom, Department of Animal and Plant Sciences, University of Sheffield, Sheffield, S10 2TN, United Kingdom

The aim of this work was to examine the effect of exposure of leaves to low temperatures (5°C) upon the contents of phosphorylated intermediates and respiration in darkened barley (Hordeum vulgare L.) plants which differed in their carbohydrate status. In leaves that had previously been illuminated for 24 hours, there was a large increase in amounts of phosphorylated metabolites at 5°C during the first 3 hours of darkness, compared with control plants kept at 30°C. Hexose phosphates accounted for about two-thirds of this increase, which reached a peak after about 3 hours. At higher temperatures, there was a peak in the amount of fructose 2,6-bisphosphate and the rate of respiration which accompanied the transient increase in phosphorylated intermediates. At 5°C the increase in phosphorylated intermediates was not accompanied by appreciable changes in fructose 2,6-bisphosphate, and there was a rapid decline in the rate of respiration. Leaves that had previously been darkened for 24 hours and that were low in carbohydrate failed to accumulate phosphorylated intermediates when exposed to low temperatures. The results are discussed with respect to the acclimation of carbohydrate metabolism to low temperatures. The results suggest that respiratory carbohydrate metabolism is strictly controlled even when the carbohydrate supply and glycolytic intermediates are abundant. The possibility that accumulation of hexose phosphates may be involved in acclimation of metabolism to low temperature is discussed.

¹ Supported by the Agricultural and Food Research Council, U.K. (Research grant PG50/67) and by the Science and Engineering Research Council, U.K. C. A. L. was supported by the British Council, by an Overseas Research Student Award, and by CNPq Brazil.

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