Plant Biomechanics Group, Botanic Garden, Faculty of Biology, University of Freiburg, Schänzlestraße 1, 79104 Freiburg, Germany.
Freiburg Materials Research Center (FMF), University of Freiburg, Stefan-Meier-Straße 21, 79104 Freiburg, Germany.
Biol Lett. 2019 Sep 27;15(9):20190254. doi: 10.1098/rsbl.2019.0254. Epub 2019 Sep 25.
, one of the most loved cut flowers, is (in)famous for the drooping of its flower heads under dehydration. This effect has been quantified by analysing both fully turgescent and wilting peduncles of 'Nuance'. Wilting peduncles display pronounced bending in the region directly below the inflorescence after 24 h of dehydration, while the rest of the peduncle remains upright. Using anatomical measurements and three-point bending tests, we have analysed whether this phenomenon is caused by mechanical and/or geometrical alterations. We have found that both the flexural rigidity and the axial second moment of area are significantly decreased in the apical part of wilting peduncles, whereas the bending elastic modulus shows no significant change. Moreover, cross-sections of wilting peduncles ovalize significantly more than those of turgescent peduncles and exhibit considerable shrinkage of the parenchyma, taking up the majority of the cross-sectional area. Generally, the drooping of wilting flowers can be regarded as a temporary instability of a rod-shaped cellular solid caused by anatomical differences (tissue arrangement, existence or the absence of a pith cavity) and geometrical changes (the decrease of axial second moment of area, cross-sectional ovalization, shrinkage of tissues) between the apical and basal regions of their peduncles.
康乃馨是最受欢迎的切花之一，以脱水后花朵下垂而闻名。本研究通过分析完全肿胀和萎蔫的 'Nuance' 花梗，对这种现象进行了量化。萎蔫花梗在脱水 24 小时后，在花序下方直接区域显示出明显的弯曲，而花梗的其余部分仍保持直立。通过解剖学测量和三点弯曲试验，我们分析了这种现象是否是由机械和/或几何变化引起的。我们发现，萎蔫花梗的顶端部分的弯曲刚性和轴向二次矩显著降低，而弯曲弹性模量没有显著变化。此外，萎蔫花梗的横截面比肿胀花梗明显更呈椭圆形，并且实质组织明显收缩，占据了横截面的大部分面积。总的来说，萎蔫花朵的下垂可以被认为是由于花梗顶端和基部之间的解剖学差异（组织排列、髓腔的存在或缺失）和几何变化（轴向二次矩的减小、横截面的椭圆形化、组织的收缩）导致的杆状细胞固体的暂时不稳定。
