Growth & Development

The strength of a stalk

Stalks carrying fruit may have very different stresses compared to when they carried flowers.

Adansonia digitata, the African baobab, can bear fruit up to 1.4 kg in weight. To carry that weight securely, the plant needs a strong stalk, or pedicel. New research using X-ray microtomography (µ-CT) and scanning electron microscopy (SEM) has shown how the arrangement of tissues in the pedicel can develop to support the fruit weight. The research has been published by Thea Lautenschläger and colleagues in the Annals of Botany.

The study is one of just a few into pedicel anatomy, and reveals a structure unlike tomato, another plant whose pedicels have been studied. “Our study proves that the Adansonia fruit pedicel has a fundamentally different structure than these previously investigated pedicels. Its mechanically important tissues are arranged in five main bundles and consist of strong bast fibers each surrounding a small wooden core embedded in a rather distinct parenchymatous tissue,” write Lautenschläger and colleagues in their article.

Orthoslice reconstruction of a µCT scan through a basal (A) and apical (B) part of a baobab peduncle/ pedicel transition zone. Source: Lautenschläger et al. 2020.

“The transition from the cylindrical arrangement of the strengthening bast fibers in the branch to the polystelic structure of single strands in the pedicel occurs in the peduncle and was documented in detail using µ-CT. Both structures can be considered optimized for their specific mechanical functions, i.e. carrying heavy fruits and facing different kinds of static and dynamic loading by fruit weight, wind and feeding animals.”

Polystelic, in this case, means having more than one vascular cylinder.

“From an anatomical point of view, the Adansonia digitata pedicel shows a unique organization and formation of tissues that is comparable to that of some liana cross sections. The structural arrangement composed of separate bundles most likely is optimized for bearing considerable bending and torsion loads without failure and at the same time allowing for carrying high tension loads,” the authors conclude.

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