Hyphal Wall Synthesis in Aspergillus nidulans: Effect of Protein Synthesis Inhibition and Osmotic Shock on Chitin Insertion and Morphogenesis

Pulse-labeling with N-[acetyl-(3)H] glucosamine and radioautography were used to follow the sites of chitin incorporation in hyphae of an Aspergillus nidulans mutant blocked in amino sugar synthesis. Growing hyphae incorporated N-acetylglucosamine almost exclusively at the tip. Cycloheximide addition greatly increased the label in subapical regions of the hyphae and reduced that at the tip. This effect of cycloheximide was immediate, could be reversed by removing the inhibitor, and did not appear to be due to chitin turnover. A similar change from apical to subapical N-acetylglucosamine incorporation occurred after hyphae were subjected to an osmotic shock which did not inhibit protein synthesis. The two treatments induced morphogenetic changes in the hyphae which produced abnormally large numbers of branches and septa.