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Sporangiophore development in Phycomyces is controlled by blue light. A culture grown in minimal agar in the dark will develop both macrophores and microphores, but under blue light only macrophores will develop and in higher numbers. The photographs above show a close view of a light- (left) and dark- (right) grown mycelia after removing the macrophores. Microphores supporting microsporangia (brown spheres) with spores can be clearly spotted on dark-grown mycelia. The effect of blue light is more dramatic on microphorogenesis, as can be seen in the photographs. Microphores can be easily counted under a binocular after four days of mycelial growth on minimal agar which has allowed the quantitation of the photoresponse, the determination of the sensitivity to light and action spectra of the response, and the characterization of mutants affected in this and other photoresponses. Phorogenesis in Phycomyces (both macro- and microphorogenesis) is very sensitive to blue light: the threshold is close to 10 photons per square micrometer. The phorogenesis of Phycomyces respond to light in a range of intensities of 9 orders of magnitude, a property shared with the other photoresponses of Phycomyces: phototropism, and photocarotenogenesis. Such an extraordinary wide range of response can be achieved by the use of two different photosystems optimized to operate at different light intensities. The gene products required for this and other photoresponses in Phycomyces are grouped in a phototransduction pathway.

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Method for assaying photophorogenesis