Tunicamycin‐induced growth and inhibition of glucosamine incorporation into cell walls of rice coleoptiles

Tunicamycin, 0.25 to 2.5 μ M , promotes elongation of rice coleoptile sections after a 2 h lag. Tunicamycin decreased the minimum stress‐relaxation time of the cell wall, T 0 ; and the wall loosening is recognized as the cause of this growth promotion. Bacitracin did not have significant effects on growth or T 0 except for inhibition of elongation at high concentration. Coleoptile sections were incubated with [ 14 C]‐glucosamine, and the synthetic pathway of the hexosamine‐containing cell wall component was examined by a pulse‐chase experiment. This component seems to be synthesized in the particulate fraction and secreted mainly into the hemicellulose I fraction. Tunicamycin strongly inhibited glucosamine incorporation into the particulate fraction and stopped the labeling of the cell wall. At 2.5 μ M , tunicamycin had no effect on incorporation of mannose, leucine or proline. These results suggest that the hexosamine‐containing wall component is a kind of asparagine‐linked glycoprotein, and that this component plays a principal role in formation of the cell wall network and in growth regulation.