User talk:M02odel/sandbox

My addition to the article: Phytochromes also have the ability to sense light and cause the plant to grow towards the light this is called phototropism[8] (same ref for all will put in finished article on the wiki page). Janoudi and his fellow coworkers wanted to see what phytochrome was responsible for causing phototropism to occur. So they preformed a series of experiments to figure this out that had to start at the beginning. They found that blue light causes the plant Arabidopsis thaliana to exhibit a phototropic response, this curvature is heightened with the addition of red light[8]. They found that five phytochromes are present in the plant, they also found a variety of mutants in which the phytochromes do not function properly.[8]. Two of these mutant were very important for this study they are phyA-101 and phyB-1.[8]. These are the mutants of phytochrome A and B respectively. The normally functional phytochrome A causes a sensitivity to far red light, and it causes a regulation in the expression of curvature toward the light.[8]. Whereas phytochrome B is more sensitive to the red light.[8].

The experiment consisted in the wild-type form of Arabidopsis, phyA-101, phyB-1, a mutant that expresses more than the normal amount of phytochrome A and one that expresses more than normal of phytochrome B.[8]. They were then exposed to white light as a control blue and red light at different fluences of light, the curvature was measured 70 minutes after exposure to blue light and a photographic enlarger was implemented to measure the curvature.[8]. It was determined that in order to achieve a phenotype of that of the wild-type phyA-101 must be exposed to four orders of higher magnitude or about 100umol m-2 fluence.[8]. However, the fluence that causes phyB-1 to exhibit the same curvature as the wild-type is identical to that of the wild-type.[8]. The phytochrome that expressed more than normal amounts of phytochrome A it was found that as the fluence increased the curvature also increased up to 10umol-m-2 the curvature was similar to the wild-type.[8]. The phytochrome expressing more than normal amounts of phytochrome B exhibited curvatures similar to that of the wild type at different fluences of red light up until the fluence of 100umol-m-2 at fluences higher than this curvature was much higher than the wild-type.[8].

Thus the experiment resulted in the finding that another phytochrome than just phytochrome A acts in influencing the curvature since the mutant is not that far off from the wild-type, and phyA is not expressed at all.[8]. Thus leading to the conclusion that two phases must be responsible for phototropism. They determined that the response occurs at low fluences, and at high fluences.[8]. This is because for phyA-101 the threshold for curvature occurred at higher fluences, but curvature also occurs at low fluence values.[8]. Since the threshold of the mutant occurs at high fluence values it has been determined that phytochrome A is not responsible for curvature at high fluence values.[8]. Since the mutant for phytochrome B exhibited a response similar to that of the wild-type it had been concluded that phytochrome B is not needed for low or high fluence exposure enhancement.[8]. It was predicted that the mutants that over expressed phytochrome A and B would be more sensitive. However it is shown that an over expression of phy A does not really effect the curvature, thus there is enough of the phytochrome in the wild-type to achieve maximum curvature.[8]. For the phytochrome B over expression mutant higher curvature than normal at higher fluences of light indicated that phy B controls curvature at high fluences.[8]. Overall they concluded that phytochrome A controls curvature at low fluences of light.[8].