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Summary: The Plant Cell, Vol. 1, 867-880, September 1989 O 1989American Society of Plant Physiologists
Different Roles for Phytochrome in Etiolated and Green
Plants Deduced from Characterizationof Arabídopsís
thalíana Mutants
Joanne Chory,"~b.'Charles A. Peto,' Megan Ashbaugh," Rebecca SaganichYbLee Pratt,d and
Frederick Ausubelb
a Plant Biology Laboratory,The Salk Institute, P.O. Box 85800, San Diego, California92138
Genetics, Harvard Medical School, Boston, Massachusetts 02114
Department of Molecular Biology, Massachusetts General Hospital, Boston, Massachusetts 02114, and Department of
Department of Pathology, Massachusetts General Hospital, Boston, Massachusetts 02114
Department of Botany, University of Georgia, Athens, Georgia30602
We have isolated a new complementation group of Arabidopsis fhaliana long hypocotyl mutant (hy6) and have
characterired a variety of light-regulatedphenomena in hy6 and other previously isolatedA. thaliana hy mutants.
Among six complementation groups that define the HY phenotype in A. fhaliana, three (hyl, hy2, and hy6) had
significantly lowered levels of photoreversibly detectable phytochrome, although near wild-type levels of the
phytochrome apoprotein were present in all three mutants. When photoregulationof chlorophylla/b binding protein
(cab) gene expression was examined, results obtained depended dramaticallyon the light regime employed. Using
the red/far-red photoreversibility assay on etiolated plants, the accumulation of cab mRNAs was considerably less
in the phytochrome-deficientmutants than in wild-typeA. fhaliana seedlings. When grown in high-fluencerate white
light, however, the mutants accumulated wild-type levels of cab mRNAs and other mRNAs thought to be regulated
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