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Seasonal variations of starch and soluble carbohydrates as well as extractable activities of enzymes involved in starch and maltose metabolism from 4‐year‐old twigs wood of Populus × Canadensis Moench ‘ robusta ’ were analysed during late winter, spring, and summer. A rapid decline of all enzymes occurred before or shortly after bud break in spring, accompanied by the complete degradation of starch and maltose. The inactivation proceded in a highly ordered sequence. Starch‐ and maltose‐synthesizing enzymes. March phosphorylase (EC 2.4.1.1), and D‐enzyme, (EC 2.4. 125) declined before hydrolysis of carbohydrates, while certain electrophoretic isoforms of amylases and maltose‐degrading enzymes persisted until the storage compounds were digested. The enzymes of starch synthesis, ADP glucose pyrophosphorylase (EC 2.7.7.27) and starch synthase (EC 2.4.1.21). increased already in late spring while the activity of all other enzymes stayed on a very low level during summer. Comparison of enzyme activities and rate of renewed starch deposition in June showed that both steps, catalysed by ADP glucose pyrophosphorylase and starch synthase. may be rate limiting.
Witt et al. (Thu,) studied this question.