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Correct Answer: it is responsible for geotropic response in roots; and promotes the onset of dormancy.
abscisic acid (aba) is a plant hormone that plays a critical role in regulating various plant functions, including stress responses, seed dormancy, and germination. it is chiefly known as a growth inhibitor and its effects are evident in several physiological processes within plants.
one of the primary roles of abscisic acid is to promote the onset of dormancy. this process is crucial for plants as it helps them survive adverse weather conditions, particularly during cold seasons. aba levels increase as environmental conditions become less favorable for growth, such as during the fall when daylight hours decrease. high concentrations of aba inhibit growth processes and induce dormancy in parts of the plant like buds, seeds, and even the cambium layer in stems. this dormancy ensures that the plant conserves energy and resources until favorable conditions return.
contrary to promoting fruit ripening or initiating cell division, aba generally slows down these processes. it acts as an antagonist to growth-promoting hormones like gibberellins and cytokinins. for example, in seeds, aba counteracts the effects of gibberellins, which promote germination. high aba levels ensure that the seeds remain dormant until the conditions are right for germination, preventing premature sprouting that could be detrimental to the seedling's survival.
regarding the geotropic response—how plants grow in response to gravity—aba also plays a role, although it is not as direct as its influence on dormancy. in roots, aba can influence how cells respond to gravity, affecting root growth patterns and ensuring that roots grow downwards, anchoring the plant and seeking water and nutrients. this geotropic effect helps plants maintain stability and absorb essential resources effectively.
lastly, it's important to clarify that aba does not typically stimulate the production of ethylene, another plant hormone involved in processes like fruit ripening and senescence. instead, high concentrations of aba generally lead to a reduction in processes promoted by ethylene, such as fruit ripening and leaf abscission.
in summary, abscisic acid is a multifaceted hormone with predominant roles in inhibiting growth, promoting dormancy, and modulating stress responses in plants. its functions are essential for plant survival and adaptation to environmental stresses.
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