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Gravitropism in a starchless mutant of Arabidopsis: implications for the starch-statolith theory of gravity sensingThe starch-statolith theory of gravity reception has been tested with a mutant of Arabidopsis thaliana (L.) Heynh. which, lacking plastid phosphoglucomutase (EC 2.7.5.1) activity, does not synthesize starch. The hypocotyls and seedling roots of the mutant were examined by light and electron microscopy to confirm that they did not contain starch. In upright wild-type (WT) seedlings, starch-filled plastids in the starch sheath of the hypocotyl and in three of the five columellar layers of the root cap were piled on the cell floors, and sedimented to the ceilings when the plants were inverted. However, starchless plastids of the mutant were not significantly sedimented in these cells in either upright or inverted seedlings. Gravitropism of light-grown seedling roots was vigorous: e.g., 10 degrees curvature developed in mutants rotated on a clinostat following a 5 min induction at 1 g, compared with 14 degrees in the WT. Curvatures induced during intervals from 2.5 to 30 min were 70% as great in the mutant as the WT. Thus under these conditions the presence of starch and the sedimentation of plastids are unnecessary for reception of gravity by Arabidopsis roots. Gravitropism by hypocotyls of light-grown seedlings was less vigorous than that by roots, but the mutant hypocotyls exhibited an average of 70-80% as much curvature as the WT. Roots and hypocotyls of etiolated seedlings and flower stalks of mature plants were also gravitropic, although in these cases the mutant was generally less closely comparable to the WT. Thus, starch is also unnecessary for gravity reception in these tissues.
Document ID
20040089595
Acquisition Source
Legacy CDMS
Document Type
Reprint (Version printed in journal)
Authors
Caspar, T.
(Michigan State University East Lansing 48824, United States)
Pickard, B. G.
Date Acquired
August 21, 2013
Publication Date
January 1, 1989
Publication Information
Publication: Planta
Volume: 177
ISSN: 0032-0935
Subject Category
Life Sciences (General)
Funding Number(s)
CONTRACT_GRANT: 86CRCR1-2046
CONTRACT_GRANT: DE-AC02-76ER01338
CONTRACT_GRANT: PCM-8206147
Distribution Limits
Public
Copyright
Other
Keywords
NASA Program Space Biology
Non-NASA Center
NASA Discipline Number 29-20
NASA Discipline Plant Biology

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