Comparative Studies on the Metabolic Function of Differentiated Xylem and Living Bark of Wintering Perennials1

摘要

Metabolic function of differentiated xylem cells of wintering plants was compared with that of living bark. The differentiated xylem cells generally contained the enzyme activity of the pentose phosphatase cycle, glycolytic pathway and organelles such as NADPH-linked glyoxylate reductase and NADH-linked hydroxypyruvate reductase. They also contained a NADPH-linked glutathione reductase. Thus, it was shown that the required metabolism of the differentiated xylem cells continued to function in wintering perennials.In contrast, 12 out of 34 samples of the living bark contained very low levels of glucose-6-phosphate dehydrogenase activity, and another group of 8 samples exhibited low levels of dehydrogenase activity. The remaining 11 samples exhibited various but distinct levels of enzyme activities.With the exception ofGinkgo bilobaL., both the xylem and living bark of wintering twigs contained almost the same levels of ATP, and both tissues exhibited enzyme activities in sucrose syntheses. The occurrence of NADPH-linked glyoxylate reductase in xylem tissue indicated that the plastids function in the differentiated xylem cells throughout the year.The general occurrence of substantial levels of enzyme activity and ATP in the differentiated xylem cells indicated that the xylem tissues as well as the living bark basically support the stem function in wintering stage of perennials until the time of the following onset of cambial differentiation.