PLANT PHYSIOLOGY , Vol 108, Issue 1 345-351, Copyright © 1995 by American Society of Plant Biologists
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DEVELOPMENT AND GROWTH REGULATION |
Genetic Regulation of Development in Sorghum bicolor (X. Greatly Attenuated Photoperiod Sensitivity in a Phytochrome-Deficient Sorghum Possessing a Biological Clock but Lacking a Red Light-High Irradiance Response)
K. L. Childs, J. L. Lu, J. E. Mullet and P. W. Morgan
Department of Soil and Crop Sciences, Texas A & M University, College Station, Texas 77843-2474 (K.L.C., P.W.M.)
The role of a light-stable, 123-kD phytochrome in the biological clock, in
photoperiodic flowering and shoot growth in extended photoperiods, and in
the red light-high irradiance response was studied in Sorghum bicolor using
a phytochrome-deficient mutant, 58M (ma3R ma3R), and a near-isogenic
wild-type cultivar, 100M (Ma3 Ma3). Since chlorophyll a/b-binding protein
mRNA and ribulose bisphosphate carboxylase small subunit mRNA cycled in a
circadian fashion in both 58M and 100M grown in constant light, the 123-kD
phytochrome absent from 58M does not appear necessary for expression or
entrainment of a functional biological clock. Although 58M previously
appeared photoperiod insensitive in 12-h photoperiods, extending the
photoperiod up to 24 h delayed floral initiation for up to 2 weeks but did
not much affect shoot elongation. Thus, although 58M flowers early in
intermediate photoperiods, a residual photoperiod sensitivity remains that
presumably is not due to the missing 123-kD phytochrome. Since rapid shoot
elongation persists in 58M under extended photoperiods despite delayed
floral initiation, long photoperiods uncouple those processes. The observed
absence of a red light-high irradiance response in 58M, in contrast to the
presence of the response in 100M, strengthens the suggestion that the
123-kD phytochrome missing from 58M is a phyB.
