With light and electron microscopy the substructural change and the ATPase activity of corn (Zea mays L.) root cap cells after short-term osmotic stress were studied. Some spoke-like fine strands originating from the departed periplasm and stretching towards cell wall could be observed even after plasmolysis. By observing the precipitation of ATPase activity product (lead phosphate) at plasma membrane and plasmodesmata, it was found that the fine strands were plasma membrane-lined channels surrounding the cytoplasm and that they still firmly connected to the plasmodesmata during plasmolysis. Compared with the control (unstressed), a sharp decrease of ATPase activity in the plasmodesmata of the stressed cells was observed. Inhibition of energy metabolism in these limited locales would affect the physiological activity, maybe including the regulation of permeability and the change of size exclusion limit (SEL) of plasmodesmata.
