Vegetative anatomy and mycorrhizal morphology of Schoenorchis nivea (Lindl.) Schltr., (Orchidaceae) and their adaptive significance

Balachandar, Mayakrishnan; Ravi, Ravichandran Koshila; Nagaraj, Kandhasamy; Muthukumar, Thangavelu

doi:10.14232/abs.2019.1.1-13

“…Epiphytic orchids produce roots that either remain aerial (i.e., free-hanging and not attached) or attach to a substrate. Several studies noted that attached roots are no longer spherical in shape: roots become hemispherical, with one side flattened to follow the contours of the substrate, with root hairs being restricted to the side in contact with the substrate (e.g., Dycus and Knudson, 1957;Stern and Judd, 1999;Stern, 2014;Ponert et al, 2016;Thangavelu and Ayyasamy, 2017;Balachandar et al, 2019a;Deseo et al, 2020). Root hairs of epiphytic orchids have been reported in older parts of the root as well (Dycus and Knudson, 1957;Almeida et al, 2016), further indicating that the root hairs may have other functions beside nutrient and water uptake.…”

Section: Introductionmentioning

confidence: 99%

“…Root hairs of epiphytic orchids have been reported in older parts of the root as well (Dycus and Knudson, 1957;Almeida et al, 2016), further indicating that the root hairs may have other functions beside nutrient and water uptake. Orchid root hairs also exist in various forms, apart from the usual cylindrical shape: there are branched, spiraled and club-shaped thickened versions of root hairs (Leitgeb, 1865;Balachandar et al, 2019a). Spirally cracked root hairs form mainly via the rupturing of the outer cell wall layer, which subsequently causes the inner wall layer to stretch and break (Bernal et al, 2015).…”

Section: Introductionmentioning

confidence: 99%

Getting a Grip on the Adhesion Mechanism of Epiphytic Orchids – Evidence From Histology and Cryo-Scanning Electron Microscopy

Tay

¹

,

Zotz

²

,

Gorb

³

et al. 2021

Front. For. Glob. Change

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Plants and animals evolve different attachment structures and strategies for reversible or permanent adhesion to different substrate types. For vascular epiphytes, having the ability to permanently attach to their host plants is essential for establishment and survival. Unlike mistletoe roots, roots of vascular epiphytes do not penetrate the host tissues but instead achieve attachment by growing in close contact to the surface of the substrate. However, the fundamental understanding of the attachment functions of epiphytic roots remains scarce, where majority of studies focused on the general root morphology, their functional properties and the descriptions of associated microbial endophytes. To date, research on attachment strategies in plants is almost entirely limited to climbers. Therefore, this study aims to fill the knowledge gap and elucidate the attachment functions of roots of epiphytic orchids. With the use of histology and high-resolution cryo-scanning electron microscopy (cryo-SEM) technique with freeze fracturing, the intimate root-bark substrate interface of epiphytic orchid Epidendrum nocturnum Jacq was investigated. Results showed a flattened underside of the root upon contact with the substrate surface, and the velamen layer appeared to behave like a soft foam, closely following the contours of the substrate. Root hairs emerged from the outermost velamen layer and entered into the crevices in the substrate, whenever possible. A layer of amorphous substance (glue-like substance) was observed on the surface of the root hairs. Combining the observations from this study and knowledge from previous studies, we hypothesised that epiphytic orchid roots produced a layer of glue-like substance to adhere the root to the substrate. Then root hairs are produced and enter into the voids and crevices of the substrate. This further generates a mechanical interlocking mechanism between root and substrate, thus reinforcing the attachment of the root (and hence the whole plant) to its substrate.

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“…Epiphytic orchids produce roots that either remain aerial (i.e., free-hanging and not attached) or attach to a substrate. Several studies noted that attached roots are no longer spherical in shape: roots become hemispherical, with one side flattened to follow the contours of the substrate, with root hairs being restricted to the side in contact with the substrate (e.g., Dycus and Knudson, 1957;Stern and Judd, 1999;Stern, 2014;Ponert et al, 2016;Thangavelu and Ayyasamy, 2017;Balachandar et al, 2019a;Deseo et al, 2020). Root hairs of epiphytic orchids have been reported in older parts of the root as well (Dycus and Knudson, 1957;Almeida et al, 2016), further indicating that the root hairs may have other functions beside nutrient and water uptake.…”

Section: Introductionmentioning

confidence: 99%

“…Root hairs of epiphytic orchids have been reported in older parts of the root as well (Dycus and Knudson, 1957;Almeida et al, 2016), further indicating that the root hairs may have other functions beside nutrient and water uptake. Orchid root hairs also exist in various forms, apart from the usual cylindrical shape: there are branched, spiraled and club-shaped thickened versions of root hairs (Leitgeb, 1865;Balachandar et al, 2019a). Spirally cracked root hairs form mainly via the rupturing of the outer cell wall layer, which subsequently causes the inner wall layer to stretch and break (Bernal et al, 2015).…”

Section: Introductionmentioning

confidence: 99%