Arzhanov I. Y.,Voronkova Y. S., Osadcha O. V.
Oles Honchar Dnipropetrovsk National University
TRAPPING MECHANISMS OF CARNIVIROUS PLANTS
Carnivorous plants trap insects (occasionally other small animals) and use them as an additional source of food (mainly nitrogen).There are about 19 families and 630 species of carnivorous plants, which supplement their autotrophic nutrition with heterotrophic one. As a result, carnivorous plants are less dependent on soil inorganic nitrogen necessary for the synthesis of their own proteins. Carnivorous plants are mostly perennial plants found in all parts of the world. In the CIS, there are 18 species of 4 genera, belonging to two families: the Rosyankovye and the Puzyrchatkovye. It is believed that the true carnivorous plants have evolved independently in five different groups of flowering plants. Carnivorous plants are found in all ecosystems, where flowering plants can grow from the Arctic to the tropics and from the sea level to the alpine mountain zone. They are found on all the inhabited continents, but mostly with warm, temperate and tropical climates.
Five basic trapping mechanisms are found in carnivorous plants:
– pitfall traps trap prey in a rolled leaf that contains a pool of digestive enzymes or bacteria;
– flypaper traps use a sticky mucilage;
– snap traps utilize rapid leaf movements;
– bladder traps suck in prey with a bladder that generates an internal vacuum;
– lobster-pot traps force prey to move towards a digestive organ.
These traps may be active or passive, depending on whether movement aids the capture of prey. For example, Triphyophyllum is a passive flypaper that secretes mucilage, but whose leaves do not grow or move in response to prey capture. Meanwhile, sundews are active flypaper traps whose leaves undergo rapid acid growth, which is an expansion of individual cells as opposed to cell division. The rapid acid growth allows the sundew tentacles to bend, aiding in the retention and digestion of prey.
Pitfall traps are thought to have evolved independently on at least four occasions. In general they are phytotelmata, water bodies collected or secreted into specialised containers, and ultimately held by plants for various functions such as in particular, the trapping and digestion of prey. The simplest ones are probably those of Heliamphora, the marsh pitcher plant. These plants live in areas of high rainfall in South America such as Mount Roraima and consequently have a problem ensuring their pitchers do not overflow.
The flypaper trap is based on a sticky mucilage, or glue. The leaf of flypaper traps is studded with mucilage-secreting glands, which may be short (like those of the butterworts), or long and mobile (like those of many sundews). Flypapers have evolved independently at least five times.
The only two active snap traps – the Venus flytrap (Dionaea muscipula) and the waterwheel plant (Aldrovanda vesiculosa) – are believed to have had a common ancestor with similar adaptations.
The traps are very similar, with leaves whose terminal section is divided into two lobes, hinged along the midrib. Trigger hairs inside the trap lobes are sensitive to touch. In the Venus flytrap, closure in response to raindrops and blown-in debris is prevented by the leaves having a simple memory: for the lobes to shut, two stimuli are required, 0.5 to 30 seconds apart.
Bladder traps are exclusive to the genus Utricularia, or bladderworts. The bladders (vesicula) pump ions out of their interiors. Water follows by osmosis, generating a partial vacuum inside the bladder. In aquatic species, the door has a pair of long trigger hairs. Aquatic invertebrates such as Daphnia touch these hairs and deform the door by lever action, releasing the vacuum.
To be a fully fledged carnivore, a plant must attract, kill, and digest prey; it must benefit from absorbing the products of the digestion (mostly aminoacids and ammonium ions). To many horticulturalists, these distinctions are a matter of taste. There is a spectrum of carnivory found in plants: from completely non-carnivorous plants like cabbages, to borderline carnivores, to unspecialised and simple traps, like Heliamphora, to extremely specialised and complex traps, like that of the Venus flytrap.