Seed dormancy is a natural mechanism that prevents seeds from germinating under unfavorable conditions. There are several factors that can cause seed dormancy, including:
1. Physical dormancy: Some seeds have hard seed coats that prevent water and oxygen from entering the seed, which inhibits germination. This type of dormancy can be broken down by scarification, which involves breaking or weakening the seed coat to allow water and oxygen to penetrate.
2. Chemical dormancy: Some seeds contain chemical inhibitors that prevent germination. These inhibitors can be leached out by soaking the seeds in water or by exposing them to certain environmental conditions.
3. Physiological dormancy: This type of dormancy is caused by internal factors within the seed that prevent germination. For example, some seeds require a period of cold temperatures (stratification) or exposure to light (photodormancy) before they can germinate.
4. Morphological dormancy: Some seeds have underdeveloped embryos that need to mature before they can germinate. This type of dormancy can be overcome by providing the seeds with the appropriate environmental conditions for embryo development.
5. Seed aging: Over time, seeds can lose their ability to germinate due to aging. This can be caused by exposure to high temperatures, humidity, or other environmental factors that degrade the seed's viability.
6. Environmental factors: Seeds may remain dormant in response to unfavorable environmental conditions such as extreme temperatures, lack of water, or competition from other plants. Once conditions become more favorable, the seeds may break dormancy and germinate.
Overall, seed dormancy is a complex and adaptive mechanism that allows seeds to survive in a variety of environmental conditions and ensures that germination occurs at the most opportune time for the plant's survival.
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Google Gemini AI
Jun 14
Causes of Seed Dormancy
Seed dormancy refers to a state of metabolic suppression in which germination is prevented, despite the presence of favorable conditions. This phenomenon is an adaptive trait that ensures the survival and successful establishment of plants in varying environmental conditions.
1. Physical Dormancy
- Water-impermeable seed coat: The seed coat acts as a physical barrier, preventing water uptake and subsequent germination. This type of dormancy is common in seeds with hard seed coats, such as beans and peas. - Mechanical resistance: The seed coat or endosperm exerts mechanical resistance against the imbibing seed, preventing the radicle from emerging. This is observed in seeds like walnuts and hazelnuts.
2. Physiological Dormancy
- Biochemical inhibition: Inhibitory substances, such as abscisic acid (ABA), accumulate within the seed and block the germination process. These substances must be degraded or metabolized before germination can occur. - Embryo immaturity: The embryo is underdeveloped and requires further growth and differentiation before it can initiate germination. This type of dormancy is found in viviparous seeds, which germinate while still attached to the parent plant.
3. Combined Dormancy
- Morphophysiological dormancy: Physical barriers coexist with physiological inhibition, requiring both removal of the physical obstacles and degradation of inhibitory substances for germination to proceed. This is seen in seeds like lettuce and tomato. - Endodormant dormancy: The seed coat inhibits water uptake, while the embryo is physiologically dormant. Breaking dormancy requires both physical scarification of the seed coat and metabolic activation of the embryo.
4. Environmental Dormancy
- Temperature: Seed dormancy can be induced or maintained by specific temperature ranges. For example, some seeds require a period of cold stratification (exposure to low temperatures) to break dormancy. - Light: Light can trigger or prevent seed germination. Some seeds require light to germinate (photoblastic seeds), while others are inhibited by light (scotoblastic seeds). - Water: Drought conditions can induce dormancy in some seeds as a survival mechanism.
5. Genetic Factors
- Genetic variability: Different seed populations within the same species can exhibit varying levels of dormancy, indicating a genetic basis for this trait. - Dormancy genes: Specific genes have been identified that regulate seed dormancy in several plant species. These genes encode transcription factors, enzymes, and other proteins involved in the control of physiological processes during seed development and germination.
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lisa m holbrook
Jun 14
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