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Published August 1967 | Published
Journal Article Open

Absorption and Screening in Phycomyces


In vivo absorption measurements were made through the photosensitive zones of Phycomyces sporangiophores and absorption spectra are presented for various growth media and for wavelengths between 400 and 580 mµ. As in mycelia, ß-carotene was the major pigment ordinarily found. The addition of diphenylamine to the growth media caused a decrease in ß-carotene and an increase in certain other carotenoids. Growth in the dark substantially reduced the amount of ß-carotene in the photosensitive zone; however, growth on a lactate medium failed to suppress ß-carotene in the growing zone although the mycelia appeared almost colorless. Also when diphenylamine was added to the medium the absorption in the growing zone at 460 mµ was not diminished although the colored carotenoids in the bulk of the sporangiophore were drastically reduced. Absorption which is characteristic of the action spectra was not found. Sporangiophores immersed in fluids with a critical refractive index show neither positive nor negative tropism. Measurements were made of the critical refractive indices for light at 495 and 510 mµ. The critical indices differed only slightly. Assuming primary photoreceptors at the cell wall, the change in screening due to absorption appears too large to be counterbalanced solely by a simple effect of the focusing change. The possibility is therefore advanced that the receptors are internal to most of the cytoplasm; i.e., near the vacuole.

Additional Information

© 1967 by The Rockefeller University Press. After the Initial Publication Period, RUP will grant to the public the non-exclusive right to copy, distribute, or display the Article under a Creative Commons Attribution-Noncommercial-Share Alike 4.0 International license, as described at https://creativecommons.org/licenses/by-nc-sa/4.0/legalcode, or updates thereof. Received for publication 3 November 1966. The authors want to thank Derek Fender for helpful discussions on the optical properties of sporangiophores, and for computer help in the determination of the light paths through the model system making possible estimates of the effects of focusing. The authors also wish to thank Walter Shropshire for his helpful discussions on phototropism in fluorochemicals and on the location of photoreceptors, Gerhardt Meissner and Charles David for the use of their unpublished data on sporangiophore extracts, and Gerold Adam for discussions concerning scattering. This work was supported by National Science Foundation Grant GB 4642. Dr. Zankel was supported by a Public Health Service Fellowship, 5-F3-GM-24,119, from the National Institute of General Medical Sciences.

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