Morphology and Anatomy of Branch–Branch Junctions in Opuntia ficus-indica and Cylindropuntia bigelovii: A Comparative Study Supported by Mechanical Tissue Quantification

Abstract

The Opuntioideae include iconic cacti whose lateral branch–branch junctions are intriguing objects from a mechanical viewpoint. We have compared Opuntia ficus-indica, which has stable branch connections, with Cylindropuntia bigelovii, 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 C. bigelovii. (ii) Older branches of O. ficus-indica 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 O. ficus-indica 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.

Elastic and collapsible: current understanding of cell walls in succulent plants

“…Another disadvantage of CoMPP is the difficulty of isolating succulent tissues within a succulent organ, which is not feasible in most cases and requires whole organs. The latest technological developments include imaging techniques that allow for three-dimensional visualization of cell wall structure, composition, and connectivity, including serial-sectioning scanning electron microscopy (ssSEM; Oi et al , 2017 ; Harwood et al, 2020 , 2021 ; Antreich et al , 2021 ) among other high-resolution microscopy techniques ( Zeng et al , 2017 ; Haas et al , 2020 ), X-ray microcomputed tomography (X-ray microCT; Théroux-Rancourt et al , 2017 ; Earles et al , 2018 ), and magnetic resonance imaging (MRI; Malik et al , 2016 ; Hesse et al , 2020 ; Mylo et al , 2021 ). These methods have the potential to elucidate how succulent tissues are built and to reveal their anatomical complexity from a three-dimensional perspective.…”

Elastic property and fracture mechanics of lateral branch-branch junctions in cacti: A case study of Opuntia ficus-indica and Cylindropuntia bigelovii

“…The measured maximum rates of the entire sample, and especially that of the junction, are markedly higher than the maximum strain values of the dermal tissues (with and without the periderm covering) and vascular bundles involved (Mylo et al, 2021a). This suggests that additionally to the deformation of the tissues involved, other processes take place enabling larger total elongation.…”

“…The rooting ability of detached O. ficus-indica branches (Gibson and Nobel, 1986) shows that vegetative propagation can also be found for this species. However, mechanical stiffening of the lateral junctions, 10.3389/fpls.2022.950860 as a result of fast branch growth and the accompanying formation of a (wound) peridermal collar around the areole from which the branch emerges (Mylo et al, 2021a), occurs even in young stages. This not only enhances the water storage capacity of the branches by increasing the amount of parenchyma tissue but at the same time the formation of the stiffening wound periderm makes the junctions less prone to mechanical failure.…”

Charting the twist-to-bend ratio of plant axes

“… tissue E (MPa) references sclerenchyma 24 500 − 45 000 [ 7 , 10 , 11 ] wood (sec. xylem)* 2600–16 000 [ 10 ] collenchyma 1000–2600 [ 7 , 10 , 12 ] vascular bundles 30–840 [ 7 , 10 , 13 ] epidermis + periderm 350–500 [ 14 ] epidermis 3–250 [ 10 , 13 , 15 ] parenchyma (non-lignified) 5–100 [ 10 ] …”

“…*Wood can differ significantly in the longitudinal, tangential and radial directions.tissue E (MPa)referencessclerenchyma24 500 − 45 000[7,10,11]wood (sec. xylem)*2600–16 000[10]collenchyma1000–2600[7,10,12]vascular bundles30–840[7,10,13]epidermis + periderm350–500[14]epidermis3–250[10,13,15]parenchyma (non-lignified)5–100[10]…”