Changes in the isozymic pattern of phosphoenolpyruvate

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Abstract
Two major isofunctional forms of phosphoenolpyruvate carboxylase (EC 4.1.1.31) have been separated from the leaves of Kalanchoe blossfeldiana Poelln. Tom Thumb by acrylamide gel electrophoresis and diethylaminoethyl cellulose techniques: one of the forms prevails under long-day treatment (low crassulacean acid metabolism level), the other develops under short-day treatment (high Crassulacean acid metabolism level). Molecular weights are significantly different: 175·103 and 186·103, respectively. These results indicate that two populations of phosphoenolyruvate carboxylase are present in the plant, one of which is responsible for Crassulacean acid metabolism activity under the control of photoperiod. The Crassulacean acid metabolism appears to depend on the same endogenous clock that governs other photoperiodically controlled events (e.g. flowering). The metabolic and energetic significance of this feature is discussed. It is suggested that modification in isozymic composition could be an early step in the response to photoperiodism at the metabolic level.