Perbal G, Driss-Ecole D, Tewinkel M, Volkmann D
Laboratoire CEMV, Universite Pierre et Marie Curie, Paris, France.
Planta. 1997 Sep;203(Suppl 1):S57-62. doi: 10.1007/pl00008115.
Space experiments have offered a unique opportunity to analyse the mechanism of gravisensing in plant roots. It has been shown that the strict structural polarity of statocytes observed on the ground is perturbed in microgravity: the amyloplasts move towards the proximal half of the cell and, at least in some cases, the nucleus becomes located further away from the (proximal) plasma membrane. It has thus been demonstrated that the amyloplasts do not move freely in the cytoplasm. Experiments using cytochalasin B (or D) have indicated that these organelles are attached to the actin network, probably by motor proteins. These findings have led to a new hypothesis on gravisensing the basis of which is that the tension in the actin filaments resulting from interaction with the statoliths would be transmitted to stretch-activated ion channels located in the plasma membrane (Sievers et al., 1991, In: Lloyd (ed) The cytoskeletal basis of plant growth and form, Academic Press, London New York, pp 169-182). Recently, it has been shown that the sensitivity of roots grown under 1 g conditions in orbit is less than that of roots grown in microgravity or under simulated weightlessness on clinostats. Since the location of the amyloplasts in microgravity is different from that in 1 g, the greater sensitivity observed could be due to different tensions in the actin network.
太空实验为分析植物根的重力感应机制提供了独特的机会。研究表明，在地面上观察到的平衡细胞严格的结构极性在微重力环境中受到干扰：淀粉质体移向细胞的近端一半，并且至少在某些情况下，细胞核变得离（近端）质膜更远。因此已经证明淀粉质体在细胞质中不是自由移动的。使用细胞松弛素B（或D）的实验表明，这些细胞器可能通过运动蛋白附着在肌动蛋白网络上。这些发现导致了一个关于重力感应的新假说，其基础是与平衡石相互作用产生的肌动蛋白丝中的张力会传递到位于质膜中的拉伸激活离子通道（Sievers等人，1991年，载于：Lloyd（编辑）《植物生长和形态的细胞骨架基础》，学术出版社，伦敦、纽约，第169 - 182页）。最近，研究表明在轨道上1g条件下生长的根的敏感性低于在微重力或回转器上模拟失重条件下生长的根。由于淀粉质体在微重力下的位置与在1g下不同，观察到的更高敏感性可能是由于肌动蛋白网络中不同的张力。
