MacCleery S A, Kiss J Z
Department of Botany, Miami University, Oxford, Ohio 45056, USA.
Plant Physiol. 1999 May;120(1):183-92. doi: 10.1104/pp.120.1.183.
Sedimentation and movement of plastids in columella cells of the root cap were measured in seedlings of wild-type, a reduced starch mutant, and a starchless mutant of Arabidopsis. To assay for sedimentation, we used both linear measurements and the change of angle from the cell center as indices in vertical and reoriented plants with the aid of computer-assisted image analysis. Seedlings were fixed at short periods after reorientation, and plastid sedimentation correlated with starch content in the three strains of Arabidopsis. Amyloplasts of wild-type seedlings showed the greatest sedimentation, whereas plastids of the starchless mutant showed no significant sedimentation in the vertically grown and reoriented seedlings. Because previous research has shown that a full complement of starch is needed for full gravitropic sensitivity, this study correlates increased sensitivity with plastid sedimentation. However, although plastid sedimentation contributed to gravisensitivity, it was not required, because the gravitropic starchless mutant had plastids that did not sediment. This is the first study, to our knowledge, to measure plastid sedimentation in Arabidopsis roots after reorientation of seedlings. Taken together, the results of this study are consistent with the classic plastid-based and protoplast-based models of graviperception and suggest that multiple systems of perception exist in plant cells.
在野生型、淀粉含量降低的突变体以及拟南芥无淀粉突变体的幼苗中，测量了根冠柱细胞中质体的沉降和移动情况。为了测定沉降，我们借助计算机辅助图像分析，在垂直和重新定向的植株中，使用线性测量以及从细胞中心起的角度变化作为指标。幼苗在重新定向后的短时间内被固定，质体沉降与拟南芥这三个品系中的淀粉含量相关。野生型幼苗的造粉体沉降最为明显，而在垂直生长和重新定向的幼苗中，无淀粉突变体的质体没有明显沉降。由于先前的研究表明，完全的重力敏感性需要完整的淀粉补充，本研究将更高的敏感性与质体沉降联系起来。然而，尽管质体沉降有助于重力敏感性，但它并非必需，因为重力无淀粉突变体的质体不会沉降。据我们所知，这是第一项在幼苗重新定向后测量拟南芥根中质体沉降的研究。综合来看，本研究结果与基于质体和基于原生质体的经典重力感知模型一致，并表明植物细胞中存在多种感知系统。
