Mylo Max D, Hesse Linnea, Masselter Tom, Leupold Jochen, Drozella Kathrin, Speck Thomas, Speck Olga
Plant Biomechanics Group @ Botanic Garden, Faculty of Biology, University of Freiburg, Schänzlestraße 1, D-79104 Freiburg, Germany.
Cluster of Excellence livMatS @ FIT-Freiburg Center for Interactive Materials and Bioinspired Technologies, University of Freiburg, Georges-Köhler-Allee 105, D-79110 Freiburg, Germany.
Plants (Basel). 2021 Oct 27;10(11):2313. doi: 10.3390/plants10112313.
The Opuntioideae include iconic cacti whose lateral branch-branch junctions are intriguing objects from a mechanical viewpoint. We have compared , which has stable branch connections, with , whose side branches abscise under slight mechanical stress. To determine the underlying structures and mechanical characteristics of these stable versus shedding cacti junctions, we conducted magnetic resonance imaging, morphometric and anatomical analyses of the branches and tensile tests of individual tissues. The comparison revealed differences in geometry, shape and material properties as follows: (i) a more pronounced tapering of the cross-sectional area towards the junctions supports the abscission of young branches of . (ii) Older branches of form, initially around the branch-branch junctions, collar-shaped periderm tissue. This secondary coverage mechanically stiffens the dermal tissue, giving a threefold increase in strength and a tenfold increase in the elastic modulus compared with the epidermis. (iii) An approximately 200-fold higher elastic modulus of the vascular bundles of is a prerequisite for the stable junction of its young branches. Our results provide, for both biological and engineered materials systems, important insights into the geometric characteristics and mechanical properties of branching joints that are either stable or easily detachable.
仙人掌亚科包括标志性的仙人掌，从力学角度来看，其侧枝与主枝的连接处是有趣的研究对象。我们将具有稳定枝条连接的[某种仙人掌名称1]与在轻微机械应力下侧枝会脱落的[某种仙人掌名称2]进行了比较。为了确定这些具有稳定连接与易脱落连接的仙人掌连接处的潜在结构和力学特性，我们对枝条进行了磁共振成像、形态测量和解剖分析，并对单个组织进行了拉伸试验。比较结果揭示了以下几何形状、形态和材料特性方面的差异：（i）朝着连接处横截面积更明显的逐渐变细有利于[某种仙人掌名称2]幼枝的脱落。（ii）[某种仙人掌名称1]的老枝最初在枝-枝连接处周围形成领状周皮组织。这种次生覆盖物使真皮组织在力学上变硬，与表皮相比，强度增加了两倍，弹性模量增加了十倍。（iii）[某种仙人掌名称1]维管束的弹性模量大约高200倍是其幼枝稳定连接的前提条件。我们的研究结果为生物材料系统和工程材料系统提供了关于稳定或易于分离的分支连接的几何特征和力学性能的重要见解。
