Gelatinous fibers develop asymmetrically to support bends and coils in common bean vines (Phaseolus vulgaris)

Premise: Gelatinous (G)-fibers are specialized fibers that generate tensile force to bend and straighten many plant organs; this phenomenon has been intensively studied in tension wood of trees. Previous work has shown that G-fibers are common within the stems of twining vines, but we lack the spatiotemporal developmental data required to determine whether, or how, G-fibers contribute to the movement and/or stabilization of twining tissues. Methods: We employed multiple histochemical approaches to characterize the formation and cell wall architecture of G-fibers in twining and shrub phenotypes of common bean across a developmental time series. Results: Within an internode, G-fibers first formed asymmetrically via differentiation of pericyclic fibers on the concave side of an existing bend and later arose erratically from the vascular cambium. G-fibers were absent in immature and/or actively circumnutating internodes, thus validating previous reports that G-fibers are not involved in rapid dynamic movements. Instead, G-fibers formed in stationary internodes, where they developed (1) in an alternating asymmetric pattern, likely to support the posture maintenance of erect internodes at the base of twiners and throughout the length of shrubs or (2) on the concave side of twined internodes to stabilize their helical conformation. Conclusions: Our spatiotemporal results indicate that common bean vines form G-fibers after an internode has fully elongated and becomes stationary, thus functioning to stabilize the posture of subtle bends and coil internodes. These results contribute to understanding how twining vines establish and maintain a grip on their host or supporting structure.