Edwards E S, Roux S J
Department of Botany, University of Texas at Austin 78713, USA.
Planta. 1998 Aug;205(4):553-60. doi: 10.1007/s004250050355.
The polarity of germinating single-celled spores of the fern Ceratopteris richardii Brogn. is influenced by gravity during a time period prior to the first cellular division designated a "polarity-determination window". After this window closes, control of polarity is seen in the downward (with respect to gravity) migration of the nucleus along the proximal face of the spore and the subsequent downward growth of the primary rhizoid. When spores are germinated on a clinostat the direction of nuclear migration and subsequent primary rhizoid growth is random. However, in each case the direction of nuclear migration predicts the direction of rhizoid elongation. Although it is the most obvious movement, the downward migration is not the first movement of the nucleus. During the polarity-determination window, the nucleus moves randomly within a region centered behind the trilete marking. While the polarity of many fern spores has been reported to be controlled by light, spores of C. richardii are the first documented to have their polarity influenced by gravity. Directional white light also affects the polarity of these spores, but this influence is slight and is secondary to that of gravity.
水蕨（Ceratopteris richardii Brogn.）萌发的单细胞孢子的极性，在首次细胞分裂之前的一段时间（称为“极性决定窗口”）受重力影响。此窗口关闭后，极性控制表现为细胞核沿孢子近端表面向下（相对于重力方向）迁移，以及随后初生假根的向下生长。当孢子在回转器上萌发时，细胞核迁移方向和随后的初生假根生长方向是随机的。然而，在每种情况下，细胞核迁移方向都能预测假根伸长方向。虽然向下迁移是最明显的运动，但并非细胞核的首次运动。在极性决定窗口期间，细胞核在以三射痕后方为中心的区域内随机移动。虽然已有报道称许多蕨类植物孢子的极性受光控制，但水蕨孢子是首个有记录表明其极性受重力影响的。定向白光也会影响这些孢子的极性，但这种影响很轻微，且次于重力的影响。
