Previous studies have assayed the gravitropic response of roots and hypocotyls of wild type Arabidopsis thaliana, two reduced‐starch strains, and a starchless strain. Because there have been few reports on inflorescence gravitropism, in this article, we use microscopic analyses and time‐course studies of these mutants and their wild type to study gravitropism in these stems. Sedimentation of plastids was observed in endodermal cells of the wild type and reduced‐starch mutants but not in the starchless mutant. In all of these strains, the short inflorescence stems (1.0–2.9 cm) were less responsive to the gravistimulus compared with the long stems (3.0–6.0 cm). In both long and short inflorescence stems, the wild type initially had the greatest response; the starchless mutant had the least response; and the reduced starch mutants exhibited an intermediate response. Furthermore, growth rates among all four strains were approximately equal. At about 6 h after reorientation, inflorescences of all strains returned to a position parallel to the gravity vector. Thus, in inflorescence stems, sedimentation of plastids may act as an accelerator but is not required to elicit a gravitropic response. Furthermore, the site of perception appears to be diffuse throughout the inflorescence stem. These results are consistent with both a plastid‐based statolith model and the protoplast pressure hypothesis, and it is possible that multiple systems for gravity perception occur in plant cells.

中文翻译：

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拟南芥缺淀粉突变体花序茎的向地性

先前的研究已经测定了野生型拟南芥、两种还原淀粉菌株和一种无淀粉菌株的根和下胚轴的向重力反应。由于关于花序向地性的报道很少，在本文中，我们使用这些突变体及其野生型的微观分析和时间进程研究来研究这些茎的向地性。在野生型和低淀粉突变体的内胚层细胞中观察到质体的沉淀，但在无淀粉突变体中未观察到。在所有这些菌株中，与长茎（3.0-6.0 cm）相比，短花序茎（1.0-2.9 cm）对重力刺激的反应较弱。在长花序茎和短花序茎中，野生型最初反应最大；无淀粉突变体的反应最小；减少的淀粉突变体表现出中等反应。此外，所有四种菌株的生长速率大致相等。在重新定向后约 6 小时，所有菌株的花序返回到与重力矢量平行的位置。因此，在花序茎中，质体的沉降可能起到加速器的作用，但不是引起向地反应所必需的。此外，感知部位似乎遍布整个花序茎。这些结果与基于质体的静石模型和原生质体压力假设一致，并且植物细胞中可能存在多个重力感知系统。所有菌株的花序返回到平行于重力矢量的位置。因此，在花序茎中，质体的沉降可能起到加速器的作用，但不是引起向地反应所必需的。此外，感知部位似乎遍布整个花序茎。这些结果与基于质体的静石模型和原生质体压力假设一致，并且植物细胞中可能存在多个重力感知系统。所有菌株的花序返回到平行于重力矢量的位置。因此，在花序茎中，质体的沉降可能起到加速器的作用，但不是引起向地反应所必需的。此外，感知部位似乎遍布整个花序茎。这些结果与基于质体的静石模型和原生质体压力假设一致，并且植物细胞中可能存在多个重力感知系统。