Abstract
Utricularia are carnivorous plants which have small hollow vesicles as suction traps that work underwater by means of negative pressure and watertightness of the entrance for capturing small animal prey. Utricularia multifida and U. westonii have specific thick-walled traps, which are triangular in a transverse section but their functioning is unclear. Some authors suggest that the trap door in U. multifida acts as a simple valve without a suction trapping mechanism. Our main aim was to check the anatomical trap characters that are responsible for possible water outflow and maintaining negative pressure as main functional parts of the active trap suction mechanism in both species. Using different microscopic techniques, we investigated the ultrastructure of external trap glands, quadrifids, glands near the entrance (bifids, monofids), and also pavement epithelium. Quadrifids of both species have a similar structure to those known in other species from the genus, which possess the suction trap mechanism. Glands near the entrance in U. multifida and U. westonii, which are responsible for water pumping in other species, are typically developed as in other species in the genus and have pedestal cells which are transfer cells. The transfer cells also occur in glands of the pavement epithelium, which is again typically developed as in other species in the genus. Simple biophysical tests did not confirm reliably neither the negative underpressure formation in the traps nor the watertightness of the entrance in both species. Our anatomical results indirectly support the hypothesis that both species have suction traps like all other Utricularia species, but the biophysical data rather suggest a passive valve mechanism.
Highlights
The carnivorous genus Utricularia L. (Lentibulariaceae) contains around 240 species which are terrestrial, aquatic or epiphytic (Taylor, 1989; Jobson et al, 2018)
The inner trap surface is covered by many large quadrifid glands, the main function of which is the secretion of digestive enzymes, while the bifid glands situated close to the trap door take part in water pumping out of the trap and in formation of a negative pressure necessary for rapid trap firing (Lloyd, 1942; Fineran, 1985; Taylor, 1989; Westermeier et al, 2017)
We focused on the ultrastructure of external trap glands, quadrifids, glands near the entrance and of the pavement epithelium; structures which are considered to be involved in the water outflow from Utricularia traps (Fineran, 1985; Heide-Jørgensen, 1989)
Summary
The carnivorous genus Utricularia L. (Lentibulariaceae) contains around 240 species which are terrestrial, aquatic (or amphibious) or epiphytic (Taylor, 1989; Jobson et al, 2018). The traps in the most species are discoid, hollow bladders, usually 1–5 mm large with a typical trap wall thickness of two cells and they are filled with trap fluid (Lloyd, 1942; Taylor, 1989; Płachno et al, 2012; Westermeier et al, 2017). They contain a variety of glands and trichomes on. Various glands could be responsible for proper Utricularia trap activity and water removal from the trap lumen to the external environment
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