[Enzymes of starch metabolism in root cap cells of Zea mays L]

In connection with the problem of the well-known stability of statolith starch, some enzymes of starch metabolism have been investigated qualitatively in the root cap cells of Zea mays L. No activity of granule-bound UDPG- and ADPG-transglucosylase (EC 2.4.1.21) could be found. In the soluble enzyme fraction of the root cap cells, on the other hand, activities of phosphorylase (EC 2.4.1.1), sucrose synthetase (EC 2.4.1.13), UDPG-pyrophosphorylase (EC 2.7.7.9), α-Amylase (EC 3.2.11), Maltase (EC 3.2.1.20), and D-enzyme (EC 2.4.1.25) were clearly shown to be present. However, no measurable activities of ADPG-pyrophosphorylase, sucrose-6-phosphate-synthetase (EC 2.4.1.14) and UDPG-dehydrogenase (EC 1.1.1.22) could be found. It is concluded that the stability of statolith starch in the root cap cells is not caused by the lack of enzymes of starch metabolism, but perhaps by a dynamic equilibrium between the degradation and the synthesis of starch. The later could proceed by the activity of phosphorylase working in the direction of starch synthesis because of removal of the inorganic phosphate by phosphorylating mitochondria accumulating in the neighbourhood of the statolith amyloplasts.