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Light Induced Concentration Changes of Adenosine-Triphosphate in Phycomyces Sporangiophores ^1,2

Radiation Biology Laboratory, Smithsonian Institution, Washington, D. C.

The concentrations of extractable adenosine triphosphate (ATP) following the induction of positive light-growth responses in Phycomyces sporangiophores by blue light stimuli have been measured by means of the luciferin-luciferase assay. The ATP concentration in the light-sensitive growing zone increases 30 to 50% within 30 seconds after the start of a light stimulus and returns to the normal adapted level within 1 minute after stimulation. The ATP concentration is constant for any level of light adaptation and is uniform along the length of sporangiophores even though the light sensitivity is confined to a growing zone less than 5 mm long. These results suggest that one of the initial biochemical steps after a light stimulus is the production of extractable ATP.

¹ Published with the approval of the Secretary, Smithsonian Institution.

² This research was supported by NSF grant G22133.