Comparative study of phototropic response & pigment content in oat & barley coleoptiles

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Abstract
A comparative study was made of photo-tropic behavior and pigment content in 1 strain of oats and 3 strains of barley, including an "albino." The oats required preillumination to repress the 1st internode, which is genetically repressed in barley. In both kinds of plants, preirradiation with red or blue light alters subsequent phototropic sensitivity and the content of both carotenoid and flavin pigments. In oats, low preirradiances enhanced and higher preirradiances inhibited subsequent phototropic sensitivity; in barley, only promotion is observed, except at extremely long preirradiances. Oat coleoptiles obey the reciprocity law within wide limits, while barley coleoptiles do not. Completely etiolated oat coleoptiles were quite photosensitive, while barley coleoptiles were not. The action spectrum for oat coleoptile phototropism showed 3 peaks in the blue, near 480, 460 and 420 m[mu], while the action spectrum for barley seemed to increase with decreasing wavelength. Oat coleoptiles were higher in both flavin and carotenoid pigments and in phototropic sensitivity than barley coleoptiles. Etiolated coleoptiles contained lutein as the major carotenoid, with [beta]-carotene appearing in quantity only after some preirradiation. "Albino" barley, which had a somewhat depressed phototropic sensitivity had lower than normal carotenoid, but approximately normal flavin. Coleoptile tips contained 3-5 times as much carotenoid and 2 times as much flavin as the base, but the pigments were qualitatively the same in both regions. Calculation of total absorbancies at the tip revealed the carotenoids and flavins to contribute approximately equally to light attenuation across the organ. In the visible region, the action spectrum for oats agreed closely both with the absorption of certain carotenoids, and with the absorption of flavins in organic solvents. In the near ultraviolet, where flavins have a strong peak matching the action spectrum peak, no carotenoid known to exist in the coleoptile absorbed heavily.