Unlike most plants that absorb nutrients through roots, plants of the Utricularia genus, commonly known as bladderworts, obtain nutrients by trapping small animals within bladders. Bladders are modified leaves that act as suction traps, capturing unwary creatures such as water fleas, fish fry, mites, nematode worms and protozoans. Once sucked into the bladder the animal is digested and its nutrients absorbed by the plant. This carnivorous strategy is a particularly valuable in aquatic or damp environments poor in nutrients. The arrangement of these bladders on the plant is illustrated in antique botanical paintings.
How do bladders work?
The bladder trap is set as water is actively pumped out of the interior by quadrifid glands, creating negative pressure and storing elastic energy in the trap. Prey such as a captured spider-mite trigger the trap by touching hairs attached to the bladder mouth, breaking the trapdoor seal and releasing the elastic pressure stored in the bladder walls, causing the mouth to buckle and open. Prey is sucked into the trap with the rapid influx of water. This suction trapping mechanism with the trapdoor opening and closing faster than the eye can see takes less than a millisecond. Trapped prey are suffocated due to a lack of oxygen in the bladder. The quadrifid glands secrete enzymes such as phosphatases to help digest animal prey and extract nutrients. The bladder also hosts a diverse community of organisms including algae, protozoans and bacterial colonies which may help digest prey and ease absorption of animal nutrients by the plant. After a bladder has been triggered the quadrifid glands pump water from the interior of the bladder to reset the trap.
Utricularia is the most successful carnivorous plant genus and bladderworts have a global distribution. There are more than 200 species of Utricularia, with diverse shapes and sizes of bladders. They are found in low nutrient environments, from lakes and bogs, to fast flowing rivers and pools of water collected in trees.
A model plant
Bladderworts are particularly amenable to scientific study because the bladders are transparent and small, facilitating 3D imaging. Using Optical Projection Tomography it is possible to capture the complex shapes of bladder traps, use live imaging to see how bladders develop and look inside them to discover internal structures. A small genome size in some species of Utricularia makes gene sequencing and genetic analysis accessible. Using a combination of 3D live imaging, mathematical modelling and genetic analysis we hope to gain an understanding of how Utricularia leaves develop and whether similar mechanisms are conserved in other vessel shaped carnivorous plants (Cephalotus), (Nepenthes) and (Sarracenia).