Modification of Pyruvate Kinase Activity in Cold-sensitive and Cold-resistant Leaf Tissues

In winter rape (Brassica napus, L., var. oleifera, cv. Górczański) and cucumber (Cucumis sativus, L., var. Inspektowy Warszawski) plants we found two types of pyruvate kinase. These were distinguished by different pH, ion and substrate requirements, as well as by their response to such negative modulators as ATP and alanine. Their response to temperature change was also different: the Arrhenius plot for the cucumber enzyme was linear over the temperature range 30°C to 0°C whereas that for the winter rape enzyme showed a break in the slope of the plot at 8°C. The cucumber enzyme extracted from plants exposed to chilling temperature (3°C) showed a transient increase of activity during the first days of cold treatment. The activity markedly decreased only after a pronounced (80%) protein degradation had occurred. Cold (2°C) acclimation of winter rape plants resulted in lower sensitivity of the enzyme to ATP, loss of sensitivity to alanine and decreased sensitivity to temperature below 10°C. The results are discussed in terms of plant adaptation to different temperature conditions of the environment.