Describe the general role of plant hormones and target cells. Be able to list the five types of hormones found in most flowering plants. Auxins promote cell elongation in coleoptiles and stems and are involved in phototropism and gravitropism. Gibberelins promote stem elongation, might help break dormancy of seeds and buds, and stimulate starch breakdown. Cytokinins promote cell division, promote leaf expansion, and retard leaf aging.
Abscisic acid promotes stomatal closure and bud and seed dormancy.
Ethylene promotes fruit ripening and abscission of leaves, flowers, and fruits. Apical dominance is the hormonal effect that inhibits lateral bud growth while plant resources are diverted to stem elongation. Through interactions with the environment , a flowering plant adjusts its growth patterns. Describe and give examples of phototropism, geotropism, and thigmotropism. Phytochrome serves as a switching mechanism in the biological clock governing photoperiodism.