SUMMARY: conidiophores are positively phototropic to unilateral stimulation with white light. The response is restricted to the apical 240 μ of the conidiophore. The curvatures start about 22 min. after the onset of stimulation and proceed at a rate of about 2.5° min.. During the response the rate of extension of the proximal wall (with respect to the direction of the incident illumination) decreases by about 5 % as compared to its previous rate of growth, whilst that of the distal wall increases by about 5 %; thus there is no net change in the rate of wall growth during phototropism. The sign of the phototropic response is reversed when conidiophores are unilaterally stimulated with ultraviolet radiation (280 mμ) or with white light whilst submerged in liquid paraffin. Conidiophores cultured on media containing 1-lyxo-flavin or diphenylamine show normal phototropic responses.

A tenfold increase or decrease in light intensity is followed after approximately 12 min. by a slight change (about 11 %) in the rate of conidiophore growth. However, changes in light intensity between 139 and 268 lux do not affect the growth rate. There is an acceleration in growth rate when conidiophores previously held in red light for some hours are re-illuminated with white light.


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