Circumnutation of rice coleoptiles: its occurrence,  regulation by phytochrome, and relationship  with gravitropism.
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.
Yoshihara
Takeshi
T
Botanical Gardens, Graduate School of Science, Osaka City University, Kisaichi, Katano-shi, Osaka, Japan.
Iino
Moritoshi
M
D018548:Cotyledon / Q000254:growth & development* / Q000528:radiation effects; D003624:Darkness; D018522:Gravitropism / Q000528:radiation effects*; D008027:Light; D012275:Oryza / Q000235:genetics / Q000254:growth & development* / Q000528:radiation effects*; D010834:Phytochrome; D051942:Phytochrome A; D018520:Plant Shoots / Q000254:growth & development / Q000528:radiation effects; D030821:Plants, Genetically Modified / Q000528:radiation effects; D017346:Protein Serine-Threonine Kinases
D051942:Phytochrome A; D010834:Phytochrome; D017346:Protein Serine-Threonine Kinases