Action Spectrum for Inhibition of Stem Growth in Dark-Grown Seedlings of Albino and Nonalbino Barley (Hordeum vulgare)

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Abstract
Growth in length of the 2d internode of dark-grown barley seedlings can be inhibited by a relatively small amt. of radiant energy given at 1 or more times. Both potentially green and albino seedlings of barley were sensitive to radiation, and in the var. Colsess I, which was studied in detail, they were approx. equal in sensitivity. The action spectra for control of growth of the 2d internode of dark-grown potentially green and albino Colsess I barley seedlings were quantitatively detd. but with somewhat less precision for the albino than for the potentially green seedlings. The 2 action spectra were the same within the limits of error as those previously found for control of leaf length in dark-grown pea seedlings or control of floral induction in both long- and short-day plants. This indicated that the phenomena depended upon the same initial photoreaction. More than 1000-fold change in energy is required to pass from a small to a large inhibition of the 2d-internode length of barley, but, in the case of floral initiation, this same order of change is brought about by less than a 10-fold change in energy. The effective pigment absorbed less than 1 part in 100,000 of the radiation incident on an albino barley seedling, even in the region of its max. absorption in the red portion of the spectrum.