The Mechanism of Opening and Closing Trap Door - Essay Example

Trap Structure of Utricularia australis Trap Structure of Utricularia australis This paper examines the structure of the Carnivorous bladderworts (Utricularia aceustralis) traps. As the name suggests, this is a plant that possess special suction traps that serves to trap prey mostly small insect larvae, corepods, Rotifers, Ciliates as well as phytoplanktons such as algae and cyanobacteria (Alkhalaf, Hubener, & Porembski, 2009). Alkhalaf Et.al (2008) further points out that most the Utricularia australis normally colonizes open habitats with scarce macronutrients and in turn compensate this deficiency through attracting, trapping and subsequently digesting small animals from which they derive nitrogenous nutrients. The bladderworts (Utricularia sp) are characterized by possession of some rather tremendously complex structures used for trapping known as suction bladders (Alkhalaf, Hubener, & Porembski, 2009). These highly specialized suction bladders are also responsible for digestion as well as absorption of captured prey. Utricularia tend to grow in marshy habitat, in streaming water or stationary water extending their roots up to several meters below water surface (Davis, 2003). Just as the species name suggest, they are mainly found in some parts of Western Australia, South wales as well as Victoria and Tasmania. The structure of the Trap The suction traps are discoid in shape and hollow with a foliar origin. Their hollow cavity with an average length of about 2.5mm, referred to as the bladder, is filled with water. The bladder is made of a wall thickness of two cells (Adamec, Functional characteristics of traps of aquatic carnivorous Utricularia species, 2011). In the two differing layers of cells, cells in the inner layer are elongated and arranged in a radial manner around the hinge region centrally located. These cells appear to be in concentric circular lines that reveals a constriction of the cells within this region. Thus these constrictions have been deemed to act as pre-folds to increase flexibility in opening and closing the trap door. The bladder also has a glandular layer with a variety of glands as well as trichomes which are also located on the outer surface of the bladder. From the roof of the bladder, there is a beak-like extension that forms a canopy over the entrance curving downwards frontwards such that the base of the beak-like canopy is opposite the base of the trap. The entrance of the bladder is tubular with a very much in-slopping-like door. Similarly, on the external side of the trap door there are trigger hairs, which when touched by a prey organism, they stimulate the opening of the trap door thereby making the prey to suctioned into the trap before the door closes again to create a water tight seal (Adamec, Photosynthetic CO2 affinity of the aquatic carnivorous plant Utricularia australis (Lentibulariaceae) and its investment in carnivory, 2009). In Utrucularia austali, the traps are regarded to be of great structural and energetic benefit. They normally alter the percentage of the trap biomass depending on their certain habitat factors such availability of prey (Adamec, Sirova, Vrba, & Rejmankova, 2010). As a matter of fact, nearly 55% of the plant’s total biomass is formed by the traps. Both the internal and external glands serve to secrete mucilage that attracts organisms into the traps. This is the case especially when capturing the free floating phytoplankton that cannot move by themselves. It has been documented that in some instances, the traps establishes a mutual existence with some of the captured preys especially phytoplankton, where the traps serve as safe habitats to the phytoplankton whereas the latter provides the plant with nitrogenous products released by these organisms (Alkhalaf, Hubener, & Porembski, 2009). Development of trap In terms of the developmental stage of the trap, Adamec (2009) points out that traps begin to form as early as possible since they form a very basic organ. This is the case because their chlorophyll content and photosynthesis are greatly reduced and therefore have to rely on other means of obtaining nutrients or energy. Some researchers have also presented that development of traps begin at an early stage when the plant germinates as a compensatory strategy to their lack of roots. The traps are a modification to a flower for this particular plant and thus are located on the stalks. According to Adamec et.al (2011) trap development is an ecophysiological adaptation that allows the plant to acquire the same very inadequate mineral nutrient reserves. This in turn ensures that plants grow very rapidly especially in their nutrient-poor habitats. Mechanism of opening and closing of the trap Despite the fact that there are no clear explanation of the mechanism of opening and closing trap door, Vincent, Roditchev, and Marmottant (2011) present that recent studies on time-resolved analysis of the opening and closing of the trap have provided an insight of the mechanical role of the trap door as some kind of buckling valve. Moreover, these studies have also revealed that one trap can fire spontaneously without any external stimulation. Firing is the trigger mechanism that opens and closes to trap a prey. In some Utricularia species, fluctuations of environmental factors such as intensity of light as well as temperature are believed to have an influence in the opening and closing of the trap. In some instances, however, the opening mechanism can be compared to an elastic instability referred to as buckling, which can be regarded as a “mechanical process where an elastic membrane (such as the trap) resisting pressure difference, suddenly changes its curvature at a critical pressure difference” (Vincent et.al 2011). Underwater traps of Utricularis usually catch prey through a repetitive process of an active slow deflation that precedes a passive fast suction. Hypothetically, the trap door tend to acts as an elastic valve that bulges as a result of a combination of pressure forces and mechanical stimulation of trigger hairs rather than just a panel interconnected on hinges (Vincent et.al 2011). According to Ademec et.al (2010), there exists an excitatory step in the trigger hairs that are located on the trap door. In some studies that have been conducted, a weak brushing on the trigger hairs resulted in firing. These hairs are in form of stiff bristles that normally projects from the trap door. The opening of the trap is believed to emanate from a deflation which is consequently due to pumping out of water from the trap when it becomes full. Adamec et.al (2010) posits that the firing as well as resettling of traps in utricularia australis are as a result of water flow and change in trap volume. The removal of water then causes a reduction in pressure inside the trap that becomes slightly lower than the external pressure surrounding the trap. This subsequently implies that the pressure difference, which is the difference between external and internal pressure, exerted on the trap door also increases. Thus, in case there is a given standard pressure difference that can trigger the opening of the door, the door will open when the increase in pressure difference reaches that point. Afterwards, the opening of the trap door reduces the pressure to zero due to the resulting deflation. The process continues as soon as the door closes. Vincent et.al (2011) however notes that in the case where the pressure difference does not meet the standard pressure, rather than firing spontaneously, the trap will remain in a waiting phase, waiting for another trigger. Functions of the trap Yang, Liu, & Chao (2008) elucidates three functions of the glands found on both sides of the trap though the internal glands have been established to play more significant roles than the externally located ones. Among these functions include; secretion of digestive enzymes, escpecially hydrolytic enzymes and amylase, absorption of digestible products and removal of excess water from the traps. Studies of the morphology of glands have helped in the generic classification of other utriculularia species. The external glands of the Utricularia can be Type I, Type II or Type III. Type one glands have domed terminal cells that lack stalks and are mainly laterally located on the wall of the trap. Type II glands are Obovoid cells that have stalks located on the valve. On the other hand, Type III glands have round cells with long stalks and are normally located around the trap doors. Most common type of glands found in Utricularia australis are normally Type II and III. Similarly, there exist two types of internal glands: chamber glands and threshold glands and are normally sessile and have terminal cells. The chamber glands are quadrifids meaning they have four arms, which has sometimes served as a basis for classification of the plant. References Adamec, L. (2009). Photosynthetic CO2 affinity of the aquatic carnivorous plant Utricularia australis (Lentibulariaceae) and its investment in carnivory. The Ecological Society of Japan, 24, 327–333. Adamec, L. (2011). By which mechanism does prey capture enhance plant growth in aquatic carnivorous plants: Stimulation of shoot apex? Fundamentals of Apllied Limnology, 172(2), 178/2, 171–176. Adamec, L. (2011). Functional characteristics of traps of aquatic carnivorous Utricularia species. Aquatic Botany, 95, 226– 233. Adamec, L. (2011). The comparison of mechanically stimulated and spontaneous firings in traps of aquatic carnivorous Utricularia species. Aquatic Botany, 94, 44-49. Adamec, L., Sirova, D., Vrba, J., & Rejmankova, E. (2010). Enzyme production in the traps of aquatic Utricularia species. Institute of Botany, Slovak Academy of Sciences, 65, 273—278. Alkhalaf, I. A., Hubener, T., & Porembski, S. (2009). Prey spectra of aquatic Utricularia species (Lentibulariaceae) in northeastern Germany: The role of planktonic algae. Flora, 204, 700 – 708. Davis, G. (2003). Utricularia australis. Threatened Flora of Tasmania. Sirova, D., Adamec, L., & Vrba, J. (2003). Enzymatic activities in traps of four aquatic species of the carnivorous genus. New Phytologist, 159, 669 – 675. Vincent, O. O., Roditchev, I. I., & Marmottant, P. (2011). Spontaneous firings of carnivorous aquatic utricularia traps: Temporal patterns and mechanical oscillations. PloS One, 6(5), e20205-10. Yang, Y.-P., Liu, H.-Y., & Chao, Y.-S. (2009). Trap gland morphology and its systematic implications in Taiwan Utricularia (Lentibulariaceae). Flora, 204, 692 – 699. Read More