Kher K, Greening J P, Hatton J P, Frazer L N, Moore D
Department of Cell and Structural Biology, The University, Manchester, UK.
Mycol Res. 1992;96(10):817-24. doi: 10.1016/s0953-7562(09)81028-9.
Using video recordings we have completed the first kinetic analysis of mushroom stem gravitropism. The stem became gravireceptive after completion of meiosis, beginning to bend within 30 minutes of being placed horizontal. Stem bending first occurred in the apical 15% of its length, then the position of the bend moved rapidly towards the base, traversing 40% of stem length in 2.5 h. Meanwhile, the stem elongated by 25%, mostly in its upper half but also in basal regions. If the apex was pinned horizontally the stem base was elevated but overshot the vertical, often curling through more than 300 degrees. When the base was pinned to the horizontal (considered analogous to the normal situation), 90% of the initial bend was compensated as the stem brought its apex accurately upright, rarely overshooting the vertical. The apex had to be free to move for this curvature compensation to occur. Stems transferred to a clinostat after some minutes gravistimulation showed curvature which increased with the length of initial gravistimulation, indicating that continued exposure to the unilateral gravity vector was necessary for continued bending. Such gravistimulated stems which bent on the clinostat subsequently relaxed back towards their original orientation. Reaction kinetics were unaffected by submergence in water, suggesting that mechanical events do not contribute, but submerged stems bent first at the base rather than apex. In air, the gravitropic bend appeared first near the apex and then moved towards the base, suggesting basipetal movement of a signal. In water, the pattern of initial bending was changed (from apex to base) without effect on kinetics. Taken together these results suggest that bending is induced by a diffusing chemical growth factor (whose extracellular propagation is enhanced under water) which emanates from the apical zone of the stem. The apex is also responsible for regulating compensation of the bend so as to bring the tip to the vertical. The nature of this latter stimulus is unknown but it is polarized (the apex must be free to move for the compensation to occur) and it may not require reference to the unilateral gravity vector.
我们通过视频记录完成了对蘑菇柄向地性的首次动力学分析。减数分裂完成后，菌柄开始具有重力感受性，在水平放置后30分钟内开始弯曲。菌柄弯曲首先发生在其长度的顶端15%处，然后弯曲位置迅速向基部移动，在2.5小时内移动了菌柄长度的40%。与此同时，菌柄伸长了25%，主要是在上半部分，但基部区域也有伸长。如果顶端被水平固定，菌柄基部会抬高，但会超过垂直位置，常常卷曲超过300度。当基部被固定在水平位置（被认为类似于正常情况）时，随着菌柄将顶端精确地直立起来，90%的初始弯曲会得到补偿，很少会超过垂直位置。为了发生这种弯曲补偿，顶端必须能够自由移动。在重力刺激几分钟后转移到回转器上的菌柄显示出弯曲，弯曲程度随着初始重力刺激时间的延长而增加，表示持续暴露于单侧重力向量对于持续弯曲是必要的。这种在回转器上弯曲的经重力刺激的菌柄随后会朝着其原始方向松弛回去。反应动力学不受浸泡在水中的影响，这表明机械事件不起作用，但浸泡在水中的菌柄首先在基部而不是顶端弯曲。在空气中，向地性弯曲首先出现在顶端附近，然后向基部移动，表明信号是向基部移动的。在水中，初始弯曲模式发生了变化（从顶端到基部），但对动力学没有影响。综合这些结果表明，弯曲是由一种扩散的化学生长因子诱导的（其细胞外传播在水下会增强），该因子从菌柄的顶端区域发出。顶端还负责调节弯曲的补偿，以便将顶端带到垂直位置。后一种刺激的性质尚不清楚，但它是极化的（顶端必须能够自由移动才能发生补偿），并且可能不需要参考单侧重力向量。
