User:Kay Kang 1/Dioscorea

Wild Yam (Dioscorea) is a vine that is invasive, deciduous, and herbaceous. This species is native to Asia, though, in the U.S., it is commonly found in Florida. They can grow over 60 feet in length. Wild yams are an important crop, as they have been used to prevent menstrual cramps, stomach cramps, and general pain for centuries. During the 1950s scientists found that the roots of wild yams contained diosgenin which is a plant-based estrogen; diosgenin is hypothesized to aid in chemical defense against herbivores. This was used to create the first birth control pills during the 60s. In addition, some Dioscorea species are rich in nutrients and antioxidants. This is beneficial in rural areas where the plant is native because it enriches the diets of individuals who live in the area. These plants grow best near canopy gaps in woodlands and rainforests. Dioscorea uses vining behavior which is useful in tropical habitats because Dioscorea grow under canopies and need to latch onto different surfaces in order to grow upwards and acquire resources.

Mechanism
Although the mechanism of Dioscorea vine behavior is unknown, it is likely that Dioscorea acts similarly to vines in terms of growth and movement behavior. Vines have a touch-sensitive component that allows them to locate and latch onto a supporting base. They use nearby plants, rocks, trees, and structures for physical support. Their touch receptors allow them to reach out and sense objects. Vines seek out these surfaces by sending out shoots to assess the area. This behavior is dependent on the species, but these shoots typically move in a clockwise or counterclockwise direction, induced by circadian rhythms. When the vine makes contact with an object, the tendril shoot will coil around the object; this is a reaction called thigmotropism. This tendril can control the amount of tension and squeeze the object to stay attached to it and prevent falling. Leaf growth is typically postponed until the relative stem has secured support. When leaf growth is delayed, shoot growth is hastened. Some vines produce an adhesive on their stems that contain calcium to better latch onto structures. A gradient is produced and the calcium exits cells to spread over stems. Furthermore, Dioscorea is a twiner, this means that the plant undergoes circumnutation which is a helical movement that allows stems to wrap around objects. In order for this mechanism to take place, endodermal cells, plasmodesmata, the plasma membrane, epidermal cells, calcium, potassium, chloride, and proton pumps are required. The SCR gene is also crucial for twining to occur. To better understand the physiology of Dioscorea further research must be conducted as much has still not been discovered.

Experiment
In 2009, an experiment was conducted to address the mechanism of force generation in the twining plant, Dioscorea bulbifera. To do this, the authors used a mechanical pole that measured the squeezing force of the twining vine. Plants were grown in a greenhouse setting, and once the shoots of the plants started “circumnutating,” a pole was introduced to allow for twining around the object. Authors found that the amount of force being applied to the pole when the vine is twining is due to the stretching of the stipule. The forces of the bending and twisting motion of D. bulbifera did not generate a measurable force. In addition, this experiment indicates that stipules are not the only driving force for tension in vines and that they contribute to increased squeezing force later in development. (Isnard et al. 2009).

Overall, Dioscorea has a vining mechanism that allows it to obtain nutrients while living under a canopy; it has evolved to do this by seeking out surfaces to climb and latch onto. Vines, like Dioscorea, have touch-sensitive components that allow them to specialize in this behavior.