Fungi Online

Diagram illustrating the ultrastructure of a septate hypha

• Each HYPHA is:
  • essentially a tube - consisting of a rigid wall and containing protoplasm
  • tapered at its tip - this is the region of active growth (i.e. the extension zone).
• SEPTA (cross-walls), if present, can usually be observed down a light microscope
  • some fungi possess septa at regular intervals along the lengths of their hyphae
  • in others, cross-walls form only to isolate old or damaged regions of a hypha or to isolate reproductive structures.
  • some septa possess one of more PORES - such septa divide up the hyphae into a series of interconnected HYPHAL COMPARTMENTS, rather than separate, discrete cells.
• The PLASMA MEMBRANE is closely associated with the hyphal wall and in some regions may even be firmly attached to it - making it difficult to plasmolyse hyphae.
• Each hyphal cell or compartment normally contains one or more NUCLEI. In species whose septa possess a large central pore, the number of nuclei within a hyphal compartment won't remain static because the nuclei are able to pass between adjacent compartments, via the central septal pore.
• Other CYTOPLASMIC ORGANELLES are those commonly found in all eukaryotic cells.
• The GROWING TIP is structurally and functionally very different from the rest of the hypha
  • its cytoplasm appears more dense
  • there are no major organelles at the extreme tip
  • at the extreme tip there is an accumulation of membrane-bound vesicles - the APICAL VESICULAR CLUSTER (COMPLEX) (AVC) - which plays an important role in apical growth.
• VACUOLES may be visible in sub-apical hyphal compartments - although small at first, they grow larger and merge with one another; they store and recycle cellular metabolites, e.g. enzymes and nutrients.
• In the oldest parts of the hypha the protoplasm may breakdown completely, due either to AUTOLYSIS (self-digestion) or in natural environments HETEROLYSIS (degradation due to the activities of other microorganisms).

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