What Causes Plants to Become Dormant?
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Normal Conditions
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Under normal conditions, plants interact with the environment. They use sunlight, for example, to go through the process of photosynthesis, and roots absorb water. These conditions work with the pre-programmed biology of the plant and essentially tell it that it is a favorable time to grow and to produce fruit or seeds. Under these conditions, more photosynthate is produced than the plant can use--it is similar to an individual eating more food and gaining weight when food is plentiful.
Light
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As light and temperatures decrease, the plant isn't able to produce as much food for itself, because light is essential for the photosynthesis process. The growth of foliage slows, and the plant puts all its energy into surviving rather than getting bigger or producing seeds and/or fruit.
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Abscisic Acid
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Abscisic acid (ABA) is a hormone found in plants that is related to almost everything in plant dormancy. When temperatures drop, for instance, ABA is responsible for the suspension of the growth of foliage. Plants that are deficient in ABA have trouble entering dormancy. Over time, the cold breaks down the ABA in the plant. When this happens, the hormonal balance of the plant shifts and growth is once again viable.
Seed Dormancy
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Although most people think of plant dormancy occurring in plants that already have started through the growth cycle, another form of plant dormancy is seed dormancy. Seed dormancy occurs when a seed has the right temperature and environmental conditions but is prevented from germinating by the coating on the seed. Occasionally the seed coating is too thick or hard for water to penetrate and reach the embryo, and so the seed never germinates.
Plant Biology
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Because ABA plays such a crucial role in dormancy, it is important to remember that the levels of ABA vary from plant to plant, as do levels of other hormones related to growth. This is because the biological makeup of every plant species is different. Some plants are "programmed" by biology to respond sensitively to environmental conditions with dormancy, while others are not. Some plants even go dormant when environmental conditions do not alter, which is a way for the plant to conserve energy for a later time. Bulb plants, such as amaryllis, sometimes suspend foliage and flower growth in favor of bulb division, which the plant uses as a non-seed means of reproducing.
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