The structure and development of septa inNeurospora crassa

Summary Electron microscopy of septa ofNeurospora crassa has shown that microfibrillar material is a major structural component. These microfibrils are arranged in a predominantly tangential orientation and in young (24 hours) mycelium can often be seen in unextracted septal preparations. In older (5 days) mycelium they are overlain with amorphous material, which can be removed by treatment with Pronase, or by chemical extractions. The structure of septa is described and compared with that of the lateral hyphal wall.Developing septa are typically surrounded by vesicles, and sometimes by alignments of cytoplasmic tubules. Electron and light microscopic autoradiography have shown that N-acetylglucosamine is quickly and specifically incorporated into developing septa, and there is no evidence for its prior incorporation into any cytoplasmic site. Glucose is also incorporated into septa, but less specifically. From the autoradiographic results and from experiments with chemical and enzymic extractions it is suggested that chitin is a major component of the septum. A model of the septum is constructed from these data.