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Irradiance-dependent regulation of gravitropism by red light in protonemata of the moss Ceratodon purpureusApical cells of protonemata of the moss Ceratodon purpureus (Hedw.) Brid. are negatively gravitropic in the dark and positively phototropic in red light. Various fluence rates of unilateral red light were tested to determine whether both tropisms operate simultaneously. At irradiances > or = 140 nmol m-2 s-1 no gravitropism could be detected and phototropism predominated, despite the presence of amyloplast sedimentation. Gravitropism occurred at irradiances lower than 140 nmol m-1 s-1 with most cells oriented above the horizontal but not upright. At these low fluence rates, phototropism was indistinct at 1 g but apparent in microgravity, indicating that gravitropism and phototropism compete at 1 g. The frequency of protonemata that were negatively phototropic varied with the fluence rate and the duration of illumination, as well as with the position of the apical cell before illumination. These data show that the fluence rate of red light regulates whether gravitropism is allowed or completely repressed, and that it influences the polarity of phototropism and the extent to which apical cells are aligned in the light path.
Document ID
20040141814
Acquisition Source
Kennedy Space Center
Document Type
Reprint (Version printed in journal)
External Source(s)
Authors
Kern, V. D.
(Ohio State University Columbus 43210, United States)
Sack, F. D.
Date Acquired
August 22, 2013
Publication Date
September 1, 1999
Publication Information
Publication: Planta
Volume: 209
Issue: 3
ISSN: 0032-0935
Subject Category
Life Sciences (General)
Funding Number(s)
CONTRACT_GRANT: NAG10-0179
Distribution Limits
Public
Copyright
Other
Keywords
Non-NASA Center
NASA Discipline Plant Biology

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