CYTOLOGICAL EVENTS INDUCED BY THE INHIBITION OF POLYAMINE BIOSYNTHESIS IN THIN CELL-LAYERS OF TOBACCO

The proliferative growth of thin cell layers of Nicotiana tabacum cult ured on a rhizogenic medium was markedly disturbed when polyamine bios ynthesis was inhibited. Treatments with polyamine inhibitors led to ce ll expansion, accompanied by thinning of the cell wall and inhibition of cell division, and frequent cases of nucleolar extrusion, mainly in the parenchymal layer in contact with the medium. Nucleolar extrusion was not correlated with cell expansion. The highest incidence of nucl eolar extrusion occurred when the pathways of putrescine biosynthesis were inhibited and when spermidine synthesis, via S-adenosylmethionine decarboxylase, was blocked. The duration of the growth phase with nuc lear amitotic divisions was prolonged in the presence of the inhibitor s and root meristem formation delayed. When polyamines were added with the inhibitors, all reactions proceeded as in the controls.