LIGHT
-by Nadzirah Isa
Fungi might have a requirement for light. They are grown routinely in the laboratory in the dark and in nature are often found growing in the absence of light. However, it will be shown here that fungi have developed sophisticated relationships with the daily light-dark cycles , particularly with respect to the initiation of reproduction.
The action of light
Blue light which is the short wavelengths, is more effective compared to the light color with longer wavelengths.
Red light is without effect and so can be used as a ‘safe light in experiment’ in which is necessary to inoculate and grow fungi in culture under conditions which for them is dark.
It was inferred from the unknown action spectrum and later confirmed by the biochemical means, that riboflavin is the light receptor.
The required quantities of light are low , well below those of the full moon on a clear night.
The reaction chain from the photons hitting the fungus starts with their absorption by riboflavin, which then reduces b-type cytochrome , as has been found to be the case N. crasa.
Light - dark cycles
It is not the light that triggers the response but the onset of light after a dark period.
The daily light dark change has the same effect each day.
The structure induces by the light are formed repeatedly
With the bulk of mycelium growing mainly within the substrate, that reaching the surface is stimulated each morning to differentiation into reproductive structures.
When the exposed hyphae are irradiated their rate of extension is reduced, preliminary to differentiation into reproductive structures.
Those are not exposed continue to grow trophically at the original rate and eventually fill that space that would have been filled by those hyphae that have been irradiated and whose trophic growth has been terminated.
Since the mycelium spreads more or less , the reproductive structures are located in concentric rings around the origin.
This process of rhythmic growth and reproduction is important ecologically.
Rhythmic fungal growth is very familiar in nature as ‘fairy rings’
