This study is the result of experimentation on the affects of synthetic and natural auxins when used to micropropagate African violet leaf discs. The initial idea of this project was to show that Naphthalene acetic acid, the synthetic auxin, would better stimulate the growth of African violet leaf disks than Indole acetic acid. Data supported this hypothesis. To achieve these results, a medium was prepared, some of the main components being agar, a substance obtained from seaweed, and synthetic and natural auxins, Naphthalene acetic acid and Indole acetic acid. The medium was sterilized in an autoclave. African violet leaves were sterilized using bleach and were hole punched, creating leaf disks which were placed on the medium. Lids were placed on the plates of the medium and the experiment was ready to be observed and recorded. Within a few weeks, data answered the question, “Which type of auxin causes the greatest increase of growth of African violet leaf disks?” and proved the hypothesis. When applied to African violet leaf discs, Naphthalene acetic acid caused more growth and fewer deaths of leaf discs than both Indole acetic acid and the control. This project will help florists and other botanists quickly meet the demands for customers, and it will also help botanists improve the future of micropropagation.
Micropropagation is a relatively new method of plant propagation, or cloning, where plant cells are multiplied and grown. It has been used for a variety of ways, and is generally more productive than other types of traditional cloning. The technique, however, is very complicated. In this experiment, the variable of natural and synthetic auxins, or plant growth hormones, will be tested to find which type of auxin can most positively affect African violet tissue culture.
Traditional plant propagation has been used for a long time. There are many different methods of cloning, but among those there are two techniques that are often used. Grafting and rooting are both common ways to multiply plants. When you graft a plant, a portion of a plant, like a live tree branch, is inserted into a notch in another plant. The two are held together by a special grafting rubber band. They grow together for about three or four weeks, and the branch is then removed to grow as a new plant. This method is good for creating new varieties of plants; it is used to grow new types of apples when two separate species are combined through this technique. Rooting, though also common, is a very different way to multiply plants. A few of the roots of a plant are cut off and inserted into a proper medium for rooting, such as vermiculite or a sand mixture. Each root grows into a new plant, an exact copy of the plant its roots were taken from. Some cuttings, like those of willows and certain poplars, can be planted directly into a field and grow as new plants without a special medium. However, few plants would respond in this way. Other variations of rooting include taking leaves or stems from a plant and growing them in a similar way. Both of these methods are slow, but fairly reliable. Nevertheless, people everywhere are starting to turn to the faster technique, called micropropagation.
Scientists discovered micropropagation in 1902. Since then, it has been improved and used more and more, both in home gardening and high-tech laboratories. It was first used in the orchid industry in the 1950s, and now is used to multiply almost any plant. The method of micropropagation is long and complex. Tissue culture, or cells of a plant, is created simply by scraping them off; for example, African violet tissue culture will be used in this experiment. All equipment, such as glassware, must be sterilized in advance, often in an auto clave, which is basically a large pressure-cooker, as it is easy for the cells to get fungi or diseases while growing. A medium must be prepared, normally containing agar, a semisolid gel obtained from algae, sucrose, vitamins, essential minerals, and hormones. Auxins are also added, but they don’t have to be, although in this experiment they will be. When the medium is prepared, the tissue culture is placed on top of it, either in a Petri dish or in a flask with cotton sealing the top, and put in a very controlled environment. While growing, the cells split into new cells a few times, and eventually form a lump of tissue culture called a callus. Some of the culture may form roots or even shoots within a few weeks, and can be taken from the rest of the tissue culture and grown in a green house as a new plant. Through the dividing of the cells, thousands of healthy, disease-free plants can be grown from a few cells. Some of the easiest plants to micropropagate are species like grapes, orchids, chrysanthemums, and carrots, although the method works on even the hardest plants to grow. Micropropagation is by far the fastest propagation technique, and auxin only makes it even faster.
Auxin has previously been stated as a plant hormone that is preferred but not necessary for micropropagation, but it is very helpful if a gardener wants to ensure root growth. Fritz Went discovered auxin in 1926 by cutting the tips of oat plants off and placing agar tips on the cut ends, but to the side, and found that the plant bent away from the agar. Later, he realized that something spread from the plant into the agar causing it to bend. This chemical is called auxin. Since then we have a lot more information on auxin. Auxin is produced mainly in the stems, buds, young leaves, and other active parts of a plant. Plants respond to auxin depending on the concentration and location of the auxin, and a few other factors as well. However, at the right concentration, auxin will stimulate the enlargement of cells by increasing the irreversible stretching, or plasticity, of cell walls. High concentrations can kill a plant, so auxin is sometimes used for a weed killer. Auxin is also used in orchards, because if the right concentration is sprayed on the trees, then the fruit will all ripen at the same time. Orchards also use auxin to control the number or even the shape of fruit. If auxin is sprayed on a flower before pollination, then it will develop seedless fruit. Scientists have also developed synthetic auxins as well as natural ones. They include 2,4,-Dichlorophenaxyacetic acid, or 2,4-D, a-Naphthalene acetic acid, or a-NAA , 4-Amino-3,5,6,-trichloropicolinic acid, and many others. Natural auxins include indole-3-acetic acid, or IAA, phenylacetic acid, or PAA, indole-3-butyric acid, or IBA, and many others.
All in all, micropropagation has many good aspects, but some bad ones too. Although it is fast, it is also more expensive, and often needs to be done in a lab. If not done correctly, all of the plants may be rogue and mutated. If it is done correctly, there will be many healthy plants created from a very small amount of a mature plant. Micropropagation helps with responding to the market demand for plants quickly. Hopefully as the need for more plants increases, so will the efficiency of Micropropagation.
By Emma Buehrer
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