Donald Danforth Plant Science Center, 975 North Warson Road, St. Louis, MO, 62132, USA.
California State University Long Beach, 1250 Bellflower Blvd, Long Beach, CA, 90840, USA.
Am J Bot. 2020 Apr;107(4):549-561. doi: 10.1002/ajb2.1454. Epub 2020 Mar 23.
Abscission zones (AZ) are specialized cell layers that separate plant parts at the organ junction upon developmental or environmental signals. Fruit or seed abscission has been well studied in model species because of its crucial role for seed dispersal. Previous work showed that AZ localization differs among species of Poaceae and that AZ formation is histologically and genetically distinct in three distantly related grass species, refuting the idea of a broadly conserved module. However, whether AZ structure is consistent within subfamilies is unknown.
Eleven species were selected from six subfamilies of Poaceae, and their AZ was investigated using paraffin-embedded, stained material. Observations were added from the literature for an additional six species. Data were recorded on AZ location and whether cells in the AZ were distinguishable by size or lignification. Characteristics of the AZ were mapped on the phylogeny using maximum likelihood.
Abscission zone anatomy and histology vary among species, and characteristics of the AZ do not correlate with phylogeny. Twelve of the seventeen studied species have an AZ in which the cells are significantly smaller than surrounding cells. Of these, eight have differential lignification. Differential lignification is often associated with differential cell size, but not vice versa.
Neither smaller cells in the AZ nor differential lignification between the AZ and surrounding cells is required for abscission, although differential cell size and lignification are often correlated. Abscission zone anatomy does not correlate with phylogeny, suggesting its rapid change over evolutionary time.
离区（AZ）是植物器官连接处的特化细胞层，在发育或环境信号作用下将植物部分分离。由于其对种子散布的重要作用，果实或种子的脱落已在模式物种中得到了很好的研究。先前的工作表明，禾本科植物不同物种的 AZ 定位不同，并且在三个亲缘关系较远的禾本科物种中，AZ 的形成在组织学和遗传学上是不同的，这驳斥了广泛保守模块的观点。然而，在亚科内，AZ 结构是否一致尚不清楚。
从禾本科的六个亚科中选择了 11 个物种，并使用石蜡包埋、染色材料研究了它们的 AZ。另外 6 个物种的文献观察结果也被添加进来。记录 AZ 的位置以及 AZ 中的细胞是否可以通过大小或木质化来区分。使用最大似然法将 AZ 的特征映射到系统发育树上。
离区解剖结构和组织学在物种间存在差异，并且 AZ 的特征与系统发育无关。在所研究的 17 个物种中，有 12 个物种的 AZ 中的细胞明显小于周围细胞。其中，有 8 个具有差异木质化。差异木质化通常与细胞大小的差异有关，但反之则不然。
尽管细胞大小和木质化的差异通常相关，但 AZ 中的细胞较小或 AZ 与周围细胞之间的差异木质化并不是脱落所必需的。离区解剖结构与系统发育无关，这表明它在进化过程中迅速变化。
