Yoshihara Takeshi, Iino Moritoshi
Botanical Gardens, Graduate School of Science, Osaka City University, Kisaichi, Katano-shi, Osaka, Japan.
Plant Cell Environ. 2005 Feb;28(2):134-46. doi: 10.1111/j.1365-3040.2004.01249.x.
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.
研究发现，黑暗中生长的水稻（Oryza sativa L.）幼苗的胚芽鞘会在圆形轨道上进行有规律的回旋转头运动，周期约为180分钟。观察到既有顺时针运动，也有逆时针运动，但单个胚芽鞘仅持续沿一个方向旋转。光照下生长的幼苗没有表现出回旋转头运动。事实上，发现黑暗中生长的幼苗会因红光（R）脉冲而停止回旋转头运动。这种光诱导的回旋转头运动抑制被证明涉及一种仅由光敏色素A介导的FR诱导的极低光响应，以及一种由光敏色素B和/或C介导的FR可逆的低光响应。R诱导的回旋转头运动抑制与R诱导的胚芽鞘生长抑制在时间上一致，这表明前者是由后者导致的。然而，R处理后仍保留约25%的生长活性，这表明回旋转头运动受光敏色素的调控更为特异。经R处理的胚芽鞘表现出向重力性。对向重力性弯曲的生长差异进行研究发现，R反而增强了向重力性反应。结果表明，向重力性不是回旋转头运动的原因。然而，重力感知仍有可能是回旋转头运动机制的一部分。据推测，所研究的回旋转头运动有助于幼苗的地上部分在土壤中生长。
