We have examined the changes of the phosphorylase and β-amylase activities together with reducing sugars and the other constituents in the roots and leaves of sweet potatoes to study the mechanisms of the synthesis and degradation of starch in the higher plants at different stages of growth. Two species of sweet potatoes, Norin No. 1 and Gokoku, were set on June 15th in 1955 at the Mie University Farm, and offered to us at intervals of 2 weeks in September and October and at intervals of a month in November and December.
The results were as follows.
(1) While the phosphorylase activities both in tubers and leaves were found to increase gradually with growth and later to begin to decrease as the havest time was approached, the β-amylase activity was found to increase continuously in tubers through over the assay periods but to decrease in leaves in the earlier stage of growth and increase later.
The phosphorylase and amylase activities in sweet potato roots and leaves appear to be controlled by different manners.
(2) The seasonal differences of ascorbic acid contents seemed to relate with α-amylase activity at the earlier stage of growth, but thereafter became to run inversely.
(3) The reducing sugars decreased in leaves but increased markedly in roots during growth.
(4) The catalase activity in leaves was much higher than that of roots and increased with growth.
(5) We could find no difference between the used two species of sweet potatoes, Gokoku and Norin No. 1, set at the same time, regarding the seasonal changes of the contents of any of the above constituents.
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