[On the activity of synthetase and phosphorylase in maize leaves at different starch levels]

The activities of phosphorylase and synthetase in the bundle sheath cells of maize leaves were investigated in plants that as a result of different light-dark treatments contained various amounts of starch. The material coming from the dark (67 h) had almost no starch and scarcely any synthetase activity if starch granules were not added to the assay mixture as a primer. In the presence of this primer a poor synthetase activity could be detected. After 2 h in the light the leaves produced a small amount of starch and the synthetase activity increased. When starch granules were included in the test the synthetase activity was increased 3.5-fold. This value was 1.5-fold higher than the corresponding one in the dark. Plants that were in the light for 28 h contained fair amounts of starch and the synthetase activity was independent of the addition of primer. The values were 3 fold higher than those found in plants in the dark. A further increase in the synthetase activity and decrease in starch content were brought about by a dark period of 2 h following the illumination of 28 h.The total activity of phosphorylase remained high and almost constant in all these materials and did not require the addition of primer to attain a maximal value. In the material coming from the dark, the product produced by the activity of phosphorylase in absence of added primer could serve as a good primer for the synthetase. From the comparison of the amounts of starch produced in vivo under different conditions and the enzymic activities found we conclude that the first steps of starch synthesis are carried out by phosphorylase and that further on both enzymes participate in the process.