Studies on the Development of Asexual Reproductive Structures in Pilobolus

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Abstract
The formation of trophocysts (sporangial precursors) and sporangia was investigated in a strain of Pilobolus kleinii which formed these structures only after the mycelium of the fungus had been exposed to light. Determination of the action spectrum for trophocyst formation by means of the monochromator from a Beckman spectrophoto-meter indicated that light of wavelengths between 390-510 m[mu] was effective. Light of wavelengths longer than 520 m[mu] was not effective. Addition of diphenylamine (25 [mu]g/ml) suppressed all visible carotinoids but had no consistent effect on trophocyst formation. L-lyxoflavin (100 [mu]g/ml) inhibited growth and trophocyst formation. The inhibition of growth was relieved by riboflavin (10 [mu]g/ml). The inhibition of trophocyst formation was relieved completely by riboflavin and partially by increased exposure to light. The action spectrum and behavior with inhibitors suggest that it is a flavin in the mycelium which absorbs light to initiate trophocyst formation. Exposure of trophocysts to light after a period of darkness stimulated initiation of sporangio- phores.