植物细胞壁是多功能材料,可以通过控制纤维素原纤维的沉积而具有广泛的机械性能。壁的完整性需要足够均匀的原纤维分布以有效地应对壁应力。此外,具体条件,如输送木质部血管的水中的负压,可能需要更复杂的墙壁图案,例如,在原质中的乐队。纤维素原纤维的取向和图案由动态皮质微管引导。新的微管主要从母体微管成核,从而对局部微管密度产生正反馈,并有可能产生高度不均匀的模式。不均匀性确实出现在所有当前的皮层阵列模拟中,包括基于微管的成核,这表明植物细胞必须拥有一种未知的平衡机制来阻止它。这里,在模拟和实验相结合的方法中,我们表明,有限的局部募集的成核复合物到微管可以对抗正反馈,而局部微管蛋白耗竭不能。我们观察到成核复合物优先出现在微管附近的质膜上。通过将我们的实验结果纳入随机模拟,我们发现成核配合物的空间行为微妙地平衡了正反馈,这样,局部微管动力学的差异-就像在发展中一样-可以迅速将均匀的阵列变成带状阵列。我们的结果提供了有关植物细胞骨架如何进化以满足各种机械要求的见解,并大大提高了计算细胞生物学研究的预测能力。
Plant cell walls are versatile materials that can adopt a wide range of mechanical properties through controlled deposition of cellulose fibrils. Wall integrity requires a sufficiently homogeneous fibril distribution to cope effectively with wall stresses. Additionally, specific conditions, such as the negative pressure in water transporting xylem vessels, may require more complex wall patterns, e.g., bands in protoxylem. The orientation and patterning of cellulose fibrils are guided by dynamic cortical microtubules. New microtubules are predominantly nucleated from parent microtubules causing positive feedback on local microtubule density with the potential to yield highly inhomogeneous patterns. Inhomogeneity indeed appears in all current cortical array simulations that include microtubule-based nucleation, suggesting that plant cells must possess an as-yet unknown balancing mechanism to prevent it. Here, in a combined simulation and experimental approach, we show that a limited local recruitment of nucleation complexes to microtubules can counter the positive feedback, whereas local tubulin depletion cannot. We observe that nucleation complexes preferentially appear at the plasma membrane near microtubules. By incorporating our experimental findings in stochastic simulations, we find that the spatial behavior of nucleation complexes delicately balances the positive feedback, such that differences in local microtubule dynamics-as in developing protoxylem-can quickly turn a homogeneous array into a banded one. Our results provide insight into how the plant cytoskeleton has evolved to meet diverse mechanical requirements and greatly increase the predictive power of computational cell biology studies.