Department of Biology and Intercollege Program in Plant Biology, 208 Mueller Laboratory, The Pennsylvania State University, University Park, PA 16802, USA.
J Exp Bot. 2010 Sep;61(14):4097-107. doi: 10.1093/jxb/erq225. Epub 2010 Jul 23.
In response to pollination maize silks undergo an accelerated process of senescence which involves an inhibition of elongation. To gain insight into the mechanism underlying this growth response, the relationships among silk elongation kinetics, cell wall biophysical properties, pollen tube growth, and expansin protein abundance were investigated. The inhibition of silk elongation became apparent beyond 12 h after pollination. Pollinated walls were less responsive in assays of extension induced by pollen beta-expansin. Expansin protein abundance and endogenous expansin activity were not considerably reduced after pollination. Silk wall plastic compliance was significantly reduced 6 h post-pollination and beyond, suggesting that the wall undergoes structural modifications leading to its rigidification in response to pollination. The reduction in the plastic compliance occurred locally and progressively, shortly after pollen tubes traversed through a region of silk. Though numerous pollen grains germinated and initiated pollen tubes at the silk tip, the density of pollen tubes gradually declined along the length of the silk and only 1-2 reached the ovary even 24 h after pollination. These results support the notion that pollination-induced cell wall rigidification plays multiple roles in maize reproduction, including inhibition of silk growth and prevention of polyspermy.
为了响应授粉，玉米花丝经历了一个加速衰老的过程，其中包括伸长的抑制。为了深入了解这种生长反应的机制，研究了花丝伸长动力学、细胞壁生物物理特性、花粉管生长和扩展蛋白丰度之间的关系。授粉后 12 小时以上，花丝伸长的抑制变得明显。授粉壁在花粉β-扩展蛋白诱导的延伸测定中反应性较差。授粉后，扩展蛋白丰度和内源性扩展蛋白活性没有明显降低。授粉后 6 小时及以后，花丝壁的塑性顺应性显著降低，表明壁发生了结构修饰，使其在授粉时变硬。塑性顺应性的降低是局部的、渐进的，就在花粉管穿过花丝的一个区域之后不久。尽管许多花粉粒在花丝顶端萌发并启动花粉管，但花粉管的密度沿着花丝的长度逐渐下降，即使在授粉 24 小时后，也只有 1-2 个花粉管到达子房。这些结果支持这样一种观点，即授粉诱导的细胞壁僵化在玉米繁殖中发挥多种作用，包括抑制花丝生长和防止多精入卵。
