Table_1_Cellular Growth in Aerial Roots Differs From That in Typical Substrate Roots.XLSX

Background and AimsIn the roots of most vascular plants, the growth zone is small, the meristem and the elongation zone are sharply separated, and only meristematic cells divide. This statement is based almost entirely on studies with soil-rooted plants. Whether aerial roots of structurally dependent (=epiphytic/hemiepiphytic) species differ is virtually unexplored.
MethodsGrowth of aerial roots in 20 structurally dependent plant species from eight families was studied ex situ. In 12 species, we studied the anatomical structure and distribution of cortex cell lengths and rhizoderm in the growth zone.
Key ResultsAll the studied aerial roots had an open apical meristem, and mitoses were not restricted to the meristem. In contrast to belowground roots, relative growth rate did not strongly increase upon transition to the elongation zone, while elongating growth was often prolonged. Still, the relative growth rate was lower than in belowground roots in soil, and in different species, it did not change considerably compared to each other.
ConclusionsA distinct elongation zone with rapid cell growth was missing in the studied aerial roots. Rather, there was a growth zone in which division, growth, and differentiation co-occurred. We observed a generally low relative growth rate in aerial roots and a surprisingly similar initial growth pattern in spite of the diversity in taxonomy and ecology, which resembled initial cellular growth in leaves, stems, and fleshy dicotyledonous fruit.

研究背景与目的
多数维管植物的根系中，生长区狭小，分生组织（meristem）与伸长区（elongation zone）界限分明，且仅分生组织细胞发生分裂。该结论几乎全部源自对土生植物的研究，而依附性（附生/半附生）物种的气生根是否存在此类差异，目前几乎尚无相关探索。

研究方法
本研究于非原生境（ex situ）条件下，对来自8个科的20种依附性植物的气生根生长情况展开了研究。针对其中12个物种，我们分析了其生长区的解剖结构、皮层细胞长度分布及根被皮（rhizoderm）的分布特征。

主要研究结果
所有受试气生根均具有开放型顶端分生组织（open apical meristem），且有丝分裂（mitoses）并不局限于分生组织区域。与地下根系不同，气生根的相对生长速率（relative growth rate）在过渡至伸长区后并未出现显著提升，而伸长生长往往持续更久。尽管如此，气生根的相对生长速率仍低于土壤中的地下根系，且不同物种间的相对生长速率无显著差异。

研究结论
受试气生根中不存在兼具快速细胞生长的典型伸长区，取而代之的是一个细胞分裂、生长与分化共同发生的生长区。我们观察到气生根普遍具有较低的相对生长速率，且尽管不同物种在分类学与生态学特征上存在多样性，其初始生长模式却惊人地相似，这一特征与叶片、茎干及肉质双子叶果实的初始细胞生长模式相仿。