Final answer:
Abscisic acid (ABA) is a hormone that becomes active during stressful conditions, inhibiting growth and promoting dormancy in plants to ensure survival. It induces dormancy in seeds and closes stomata to conserve water, regulating the plant's growth in response to environmental stressors.
Step-by-step explanation:
Abscisic acid (ABA) commonly becomes active in response to stressful environmental conditions, such as dehydration, cold temperatures, or shortened day lengths. Its primary role is to regulate growth by opposing the effects of growth-promoting hormones such as gibberellins (GAs) and auxins. ABA inhibits stem elongation, induces dormancy in lateral buds and seeds, and closes stomata to prevent water loss during stress conditions.
For seeds, increased levels of ABA prevent germination during unfavorable conditions. As conditions improve, ABA levels decrease, allowing seeds to come out of dormancy. In plants, ABA helps to maintain dormancy in buds and signals the stomata to close when the plant experiences drought, reducing water loss and promoting survival.
In summary, ABA plays a critical role in protecting plants from premature growth during adverse environmental situations, thus ensuring their survival and proper development when favorable conditions return.