Importance of the wall for cell division and in the activity of the cytoplasm in cultured tobacco protoplasts.

When tobacco (Nicotiana tabacum L.) mesophyll protoplasts are cultivated in a medium in which osmotic pressure is maintained by using salts instead of sugars they divide 2-3 times although they never form a rigid wall which could be separated from the cytoplasm by the use of plasmolysis. Only a non-rigid pseudo-wall is present during division, showing that a rigid wall is not required for cell division. Diluting the salt medium with 5 volumes of sugar medium leads to the formation of a rigid wall as well as the initiation of sustained divisions. It is proposed that the complete wall is the place of synthesis of the substance(s) necessary for the division activity of the cytoplasm.