Department of Biophysics and Morphogenesis of Plants, University of Silesia, Katowice, Poland.
Plant Biol (Stuttg). 2010 May 1;12(3):459-68. doi: 10.1111/j.1438-8677.2009.00228.x.
A hypothesis exists that external and internal factors affect the orientation of cortical microtubules in as much as these lead to changes in cell elongation rate. Factors that stimulate elongation are proposed to lead to transverse microtubule orientation, whereas factors that inhibit elongation lead to longitudinal orientation. The elongation rate is equal to the rate of longitudinal irreversible strain in cell walls. Incubated epidermis peeled from sunflower hypocotyls does not extend unless it is stretched by loading and the pH of the incubation medium is appropriately low. Thus, peels provide a convenient model to investigate the relationship between longitudinal strain rate and cortical microtubule orientation. In the present study, it was found that peeling affects microtubule orientation. Peels were incubated for several hours in Murashige & Skoog medium (both unbuffered and buffered) to attain a steady state of microtubule orientation before loading. The effects of loading and pH on strain rate and orientation of microtubules under the outer epidermal walls were examined in three portions of peels positioned with respect to the cotyledonary node. Appropriate loading caused longitudinal strain of peels at pH 4.5 but not at pH 6.5. However, no clear effect of strain rate on microtubule orientation in the peels was observed. Independent of applied load and pH of the incubation medium, the microtubule orientation remained unchanged, i.e. orientation was mainly oblique. Our results show that strain rate does not affect cortical microtubule orientation in isolated epidermis of the sunflower hypocotyl model system, although orientation could be changed by white light.
有一种假说认为，外部和内部因素会影响皮层微管的取向，因为这些因素会导致细胞伸长率的变化。刺激伸长的因素被认为会导致横向微管取向，而抑制伸长的因素则会导致纵向取向。伸长率等于细胞壁中纵向不可逆转应变的速率。除非向日葵下胚轴的表皮被加载拉伸，并且孵育介质的 pH 值适当降低，否则孵育的表皮不会伸展。因此，表皮提供了一个方便的模型来研究纵向应变率与皮层微管取向之间的关系。在本研究中，发现剥皮会影响微管取向。在加载之前，将表皮在 Murashige & Skoog 培养基（未缓冲和缓冲）中孵育数小时，以达到微管取向的稳定状态。在相对于子叶节点定位的三个表皮部分中，研究了加载和 pH 值对表皮外皮层下微管应变率和取向的影响。在 pH 值为 4.5 时，适当的加载会导致表皮产生纵向应变，但在 pH 值为 6.5 时则不会。然而，在表皮中，微管取向没有明显的应变率效应。无论孵育介质的施加负载和 pH 值如何，微管取向都保持不变，即取向主要是斜向的。我们的结果表明，尽管白光可以改变取向，但在向日葵下胚轴模型系统的分离表皮中，应变率不会影响皮层微管的取向。
