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DIFFERENTIAL SPECTROPHOTOMETRY OF Phycomyces MUTANTS WITH ABNORMAL PHOTORESPONSES
Author(s) -
Horwitz Benjamin A.,
Trad Chafia H.,
Lipson Edward D.
Publication year - 1986
Publication title -
photochemistry and photobiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.818
H-Index - 131
eISSN - 1751-1097
pISSN - 0031-8655
DOI - 10.1111/j.1751-1097.1986.tb03587.x
Subject(s) - phycomyces , phycomyces blakesleeanus , phototropism , mutant , pigment , biology , carotenoid , biophysics , gene , chemistry , botany , biochemistry , blue light , physics , optics , organic chemistry
— The unidentified receptor pigments responsible for phototropism and other blue light responses of Phycomyces are expected to contribute only a minuscule fraction of the in vivo absorption spectra, even for carotene‐deficient ( car genotype) albino strains. The variable amount of residual carotenoids in strains with mutations in the carA gene precluded their use for the comparison of phototropism (mad) mutants with phototropically normal controls. We turned instead to carB albino strains, all of which have negligible carotene content. For various mad genes, we isolated carB mad strains by crosses and mutagenesis, and compared them with carB controls, in search of spectral differences associated with the mad photoreception defects. The spectra and their second derivatives show cytochrome bands, as well as a minor peak near 480 nm. This peak was present in carB strains, so it is probably not due to carotenoids. Strains L26 and L136 (both carB madE , but with different genetic backgrounds) showed modifications in the480–500 nm region. Sporangiophores that lacked the green material that usually interferes with in vivo spectroscopy were obtained by the addition of potassium iodide to the culture medium. Dark‐grown carB sporangiophores have a more pronounced second‐derivative peak at 480 nm than do light‐grown sporangiophores. Growth in the light, though, did not significantly alter the spectra of sporangiophores of L131 (carB madB) or L130 (carB madC). The spectral differences may be useful in the biochemical search for the receptor pigments.