Spiral root hairs in Spiranthinae (Cranichideae: Orchidaceae)
Tóm tắt
(Spiral Root Hairs in Spiranthinae (Cranichideae: Orchidaceae) Root hairs are extensions of root epidermal cells, usually unicellular and unbranched. Root hairs studies usually focus on the relevant physiological and molecular aspects and have become a well-studied model of cellular differentiation and growth. In the Orchidaceae structures such as velamen, as well as exodermal and endodermal thickening, have been considered taxonomically valuable for categorizing different groups. While velamen has been greatly studied and discussed, root hairs are rarely mentioned in the literature or are merely characterized as simple root hairs. In the present study, we characterize morphologically spiral root hairs in a broad sample species of Spiranthinae. We analyzed roots from 23 species included in 12 genera from the subtribe Spiranthinae and Prescottia stachyodes (Sw.) Lindl. (Cranichidinae) as an external group, using light microscopy and scanning electron microscopy. Spiral root hairs are a continuation of the velamen and are found among simple root hairs; they differ from the latter in the type of wall rupture displayed. Spiral root hairs occur frequently among the species we analyzed, in both epiphytic as well as terrestrial species. We believe these root hairs help increase the opening (facilitating the entrance of colonizers), improve fluid absorption, and increase adherence to the substrate. The presence of spiral root hairs may also carry taxonomic importance in studies with a broader sample of Orchidoideae.
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