Spore Germination

Any viable spore should eventually germinate. If the spore is that of a mycelial fungus germination usually involves the production of one or more germ-tubes. But before emergence of a germ-tube many spores will require an exogenous supply of nutrients to be available, will undergo hydration and swelling, and will experience an increase in metabolic activity.
Availability of nutrients:
  • Some spores are able to germinate in the absence of any exogenous nutrients in the environment because they possess sufficient ENDOGENOUS RESERVES (within the spore) to sustain initial growth of the germ-tube.
  • Others must be supplied with one or more EXOGENOUS NUTRIENTS (e.g. a carbohydrate source) before they are able to germinate.
Hydration (water uptake):
  • The presence of liquid water or a high relative humidity is essential for the germination of spores of most species - few spores are capable of germinating at low relative humidities.
  • Since most spores have a low water content, hydration is an essential first step in the germination process.
  • Water uptake is an ACTIVE PROCESS and requires a change in permeability of the spore wall.
Swelling is due to:
  • Hydration
  • Deposition of new wall material within the spore - some of which is destined to form the wall surrounding the developing germ-tube (see diagram below).
Germ-tube emergence:
Diagram illustrating spore germination.
  • The small vesicles accumulating near the plasma membrane are involved in the synthesis of new wall materials.
  • As the germ-tube develops these vesicles become arranged to form a cresent-shaped zone at the tip of the germ-tube - known as the APICAL VESICULAR CLUSTER or COMPLEX (AVC).
  • Emergence of the germ-tube through the spore wall is due to a combination of enzymic degradation of a small localised region of the spore wall and the physical pressure being exerted by the protoplasm.
  • The germ-tube may emerge from a pre-determined thinner region of spore wall (GERM PORE) or from some random site.

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