Seasonal Changes in Sorbitol-6-phosphate Dehydropenase in Loquat Leaf1

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Abstract
Seasonal changes in the sorbitol content and in sorbitol-6-phosphate dehydrogenase activity in the leaves of mature loquat tree were surveyed. The activity increased in late autumn and the content in early winter, both reaching maximums in winter and decreasing in spring. An experiment with seedlings in controlled-environment chambers was conducted. The increase in activity was induced by low temperature and coincided with the rise in the amount of enzyme as determined immunochemically. The photoperiod did not affect the activity. During the development of the spring leaves of the loquat, enzyme activity increased during the period in which a leaf had nearly reached its maximum size. The increase also paralleled the amount of enzyme as determined by the enzyme-linked immunosorbent assay (ELKA). This enzyme activity is considered to be controlled mainly by the amount of enzyme in the loquat leaf tissue.