Fukaki H, Fujisawa H, Tasaka M
Department of Botany, Faculty of Science, Kyoto University, Japan.
Plant Physiol. 1996 Mar;110(3):945-55. doi: 10.1104/pp.110.3.945.
In higher plants shoots show a negative gravitropic response but little is known about its mechanism. To elucidate this phenomenon, we have isolated a number of mutants with abnormal shoot gravitropic responses in Arabidopsis thaliana. Here we describe mainly three mutants: sgr1-1, sgr2-1, and sgr3-1 (shoot gravitropism). Genetic analysis confirmed that these mutations were recessive and occurred at three independent loci, named SGR1, SGR2, and SGR3, respectively. In wild type, both inflorescence stems and hypocotyls show negative gravitropic responses. The sgr1-1 mutants showed no response to gravity either by inflorescence stems or by hypocotyls. The sgr2-1 mutants also showed no gravitropic response in inflorescence stems but showed a reduced gravitropic response in hypocotyls. In contrast, the sgr3-1 mutant was found to have reduced gravitropic responses in inflorescence stems but normal gravitropic responses in hypocotyls. These results suggest that some genetic components of the regulatory mechanisms for gravitropic responses are common between inflorescence stems and hypocotyls, but others are not. In addition, these sgr mutants were normal with respect to root gravitropism, and their inflorescence stems and hypocotyls could carry out phototropism. We conclude that SGR1, SGR2, and SGR3 are novel genetic loci specifically involved in the regulatory mechanisms of shoot gravitropism in A. thaliana.
在高等植物中，茎表现出负向重力性反应，但其机制尚不清楚。为了阐明这一现象，我们在拟南芥中分离出了一些茎重力性反应异常的突变体。这里我们主要描述三个突变体：sgr1-1、sgr2-1和sgr3-1（茎重力性）。遗传分析证实这些突变是隐性的，分别发生在三个独立的基因座上，命名为SGR1、SGR2和SGR3。在野生型中，花序茎和下胚轴都表现出负向重力性反应。sgr1-1突变体的花序茎和下胚轴对重力均无反应。sgr2-1突变体的花序茎也没有重力性反应，但下胚轴的重力性反应减弱。相反，发现sgr3-1突变体的花序茎重力性反应减弱，但下胚轴的重力性反应正常。这些结果表明，重力性反应调控机制的一些遗传成分在花序茎和下胚轴之间是共同的，但其他成分则不是。此外，这些sgr突变体的根重力性正常，其花序茎和下胚轴能够进行向光性反应。我们得出结论，SGR1、SGR2和SGR3是拟南芥中专门参与茎重力性调控机制的新基因座。
