During autumn, a boy notices that the road is littered with orange leaves. He looks up to find that the tree is devoid of most leaves, while some of them are still falling. The phytohormone responsible for this causes ________________.

Step-by-step solution

Abscisic acid stimulates senescence of leaves by causing destruction of chlorophyll and inhibition of protein and RNA synthesis. It acts as a general plant growth inhibitor and an inhibitor of plant metabolism. ABA inhibits seed germination. ABA stimulates the closure of stomata and increases the tolerance of plants to various kinds of stresses. Therefore, it is also called the stress hormone. ABA plays an important role in seed development, maturation and dormancy. By inducing dormancy, ABA helps seeds to withstan