A PASSIONATE FREE CLIMBER: STRUCTURAL DEVELOPMENT AND FUNCTIONAL MORPHOLOGY OF THE ADHESIVE TENDRILS IN PASSIFLORA DISCOPHORA

摘要

Premise of research. Passiflora discophora is exceptional among passion flowers for its climbing strategy, using branched tendrils with terminal adhesive pads instead of coiling tendrils as typical within this family. This article investigates the structural development and morphology of these adhesive pads and aims to understand the underlying structure-function relationship of the attachment process. Based on our results, we discuss possible mechanical consequences of the tendril structure and compare our findings with similar attachment systems in unrelated species in order to identify general strategies of this mode of attachment. Methodology. We investigated the temporal development of the attachment process, including detailed studies of the morphology and anatomy of the adhesive pads, using LM with different staining procedures and SEM. Pivotal results. Young tendrils establish initial contact with a supporting substrate by interlocking with their hook-shaped tips. Touch stimuli induce the tips to develop into adhesive pads by callus-like growth of papillate epidermal cells. Fully grown pads are hemispherical on flat substrates or completely fill out larger cavities of the substrate. By apical cell division, the pad tissue perfectly mimics the microtopography of the substrate and also grows into minute gaps and fissures, establishing firm anchorage by optimal form closure. Additionally, an extracellular substance is visible at the interface between pad and substrate surface, which might act as adhesive. Conclusions. The opportunistic growth and cellular structure make the tendrils and adhesive pads of P. discophora a highly adaptive attachment system. Comparison with other not closely related taxa reveals general principles of this climbing mode, namely, (1) branched tendrils with multiple adhesive pads, (2) papillate cells establishing optimal form closure with the substrate and in some species additionally secreting adhesive substances, (3) free coiling of axes, and (4) persisting anchorage after senescence.