| Hormone | Structure | Typical activities |
|---|---|---|
| Abscisic acid* | Maintains seed dormancy; closes stomata | |
| Auxins (mainly indol | Promote stem elongation, adventitious root initiation, and fruit growth; inhibit axillary bud outgrowth, leaf abscission, and root elongation | |
| Brassinosteroids | Promote stem and pollen tube elongation; promote vascular tissue differentiation | |
| Cytokinins | Inhibit leaf senescence; promote cell division and axillary bud outgrowth; affect root growth | |
| Ethylene | Promotes fruit ripening, leaf abscission, and senescence; inhibits stem elongation and gravitropism | |
| Gibberellins (e.g., gibberellic acid) | Promote seed germination, stem growth, and ovule and fruit development; break winter dormancy; mobilize nutrient reserves in grass seeds | |
*See Chapter 37. | ||