Final answer:
Abscisic acid prevents abscission of leaves and fruits. It accumulates in response to stressful environmental conditions and inhibits stem elongation and induces dormancy. It also helps plants close their stomata to prevent water loss.
Step-by-step explanation:
The hormone that prevents abscission of leaves and fruits is abscisic acid (ABA).
ABA is a plant hormone that accumulates in response to stressful environmental conditions such as dehydration, cold temperatures, or shortened day lengths. It counters the growth-promoting effects of other hormones like gibberellins and auxins. ABA inhibits stem elongation and induces dormancy in lateral buds.
For example, when a plant is stressed due to lack of water, abscisic acid tells the stomata to close. This prevents water loss through the stomata.