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Circumnutation of rice coleoptiles: its occurrence, regulation by phytochrome, and relationship with gravitropism
Author(s) -
YOSHIHARA TAKESHI,
IINO MORITOSHI
Publication year - 2005
Publication title -
plant, cell and environment
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.646
H-Index - 200
eISSN - 1365-3040
pISSN - 0140-7791
DOI - 10.1111/j.1365-3040.2004.01249.x
Subject(s) - coleoptile , gravitropism , phytochrome , biology , phototropism , biophysics , seedling , botany , avena , phytochrome a , arabidopsis thaliana , biochemistry , arabidopsis , blue light , physics , red light , gene , mutant , optics
ABSTRACT It has been found that coleoptiles of dark‐grown rice ( Oryza sativa L.) seedlings undergo regular circumnutation in circular orbits with periods of about 180 min. Both clockwise and counter‐clockwise movements were observed, but individual coleoptiles continued to rotate only in one direction. Light‐grown seedlings did not show circumnutation. In fact, dark‐grown seedlings were found to cease circumnutating in response to a pulse of red light (R). This light‐induced inhibition of circumnutation was demonstrated to involve both a FR‐inducible very‐low‐fluence response, solely mediated by phytochrome A, and a FR‐reversible low‐fluence response, mediated by phytochrome B and/or C. The R‐induced inhibition of circumnutation showed temporal agreement with the R‐induced inhibition of coleoptile growth, suggesting that the former results from the latter. However, about 25% of growth activity remained after R treatment, indicating that circumnutation is more specifically regulated by phytochrome. The R‐treated coleoptile showed gravitropism. Investigation of the growth differential for gravitropic curvature revealed that gravitropic responsiveness was rather enhanced by R. The results suggested that gravitropism is not a cause of circumnutation. It remained probable, however, that gravity perception is a part of the mechanism of circumnutation. It is speculated that the circumnutation investigated aids the seedling shoot in growing through the soil.