September 27, 2012
Carnivorous Sundew Plant Uses Fast-Acting ‘Snap’ Tentacles To Hunt
Brett Smith for redOrbit.com - Your Universe Online
Many predators in the animal kingdom depend on a quick-strike ability to capture their prey, but a few species in the plant kingdom also have this impressive capability.
A handful of German biologists have decided to investigate the mechanisms behind the quick strikes of one plant in particular, Drosera glanduligera, a small sundew from southern Australia.
This sundew relies on its touch-sensitive tentacles to snap prey into its sticky, spoon-shaped leaf trap where the carnivorous plant digests it. Sundews often grow in soil that is poor in nutrient content and this carnivorous behavior allows them to supplement their sparse diet.
"Such plants are of particular interest to plant biologists because of their sophisticated and complex structural and mechanical adaptations to carnivory,” explained Speck.
Using high-speed video cameras, the researchers were able to capture not only the snapping action of the outer tentacles on laboratory fruit flies, but also the slower action of the sticky interior tentacles that aid in digestion of the prey.
According to the report, the prey capture takes place in two steps. First, any insect that touches a snap-tentacle is quickly lifted and then thrown onto the sticky leaf trap. Second, the interior glue-tentacles envelope the prey and slowly move it along the leaf for digestion and assimilation.
The catapult-flypaper-trap employed by D. glanduligera is more complex than most other species of sundew that rely solely on stickiness to catch their prey, the report said.
The researchers also noted that the snap tentacles were not triggered by movements of fruit flies that had already been ensnared by the glue tentacles. They also theorized that flies could re-trigger the tentacles if they were somehow able to escape the glue, although this behavior has not yet been observed.
Six of the snap tentacles were triggered and filmed under a dissection microscope using a fine nylon thread. This allowed the biologists to get a more detailed look at the hinge-action of the plant appendages.
In addition to taking detailed videos of the tentacles, the researchers carefully removed several of them using a razorblade. The tentacles were then scanned with an electron microscope to create a more detailed picture of their morphology. The study showed a distinct, gland-containing tentacle head and hinge zone, which contains fractured epidermal cells that were likely the result of cell buckling.
The report said that the snapping action is the result of two possible scenarios that were driven by hydraulic forces and added that further investigation is necessary to determine which of these scenarios is responsible. Future studies should also focus on elucidating the snapping action through electrochemical means, the researchers wrote.
The team also recommended that field studies should be conducted with plants that have had their snap tentacles removed. The capture rates of these modified plants could then be compared to an unmodified plant in an effort to see how much advantage these touch-sensitive tentacles actually convey to the sundew.