Part Seven - Flowering Plants: Form and Function 743

37. Regulation of Plant Growth 796

37.1 How Does Plant Development Proceed? 797 Several hormones and photoreceptors play roles in plant growth regulation 797 Signal transduction pathways are involved in all stages of plant development 798 The seed germinates and forms a growing seedling 798 The plant flowers and sets fruit 798 The plant senesces and dies 798 Not all seeds germinate without cues 799 Seed dormancy affords adaptive advantages 799 Seed germination begins with the uptake of water 800 The embryo must mobilize its reserves 800 37.2 What Do Gibberellins Do? 801 “Foolish seedling” disease led to the discovery of the gibberellins 801 The gibberellins have many effects on plant growth and development 802 37.3 What Does Auxin Do? 803 Phototropism led to the discovery of auxin 803 Auxin transport is polar and requires carrier proteins 803 Light and gravity affect the direction of plant growth 805 Auxin affects plant growth in several ways 805 Auxin analogs as herbicides 807 Auxin promotes growth by acting on cell walls 807 Auxin and gibberellins are recognized by similar mechanisms 808 37.4 What Do Cytokinins, Ethylene, Abscisic Acid, and Brassinosteroids Do? 809 Cytokinins are active from seed to senescence 809 Ethylene is a gaseous hormone that hastens leaf senescence and fruit ripening 810 Abscisic acid is the “stress hormone” 811 Brassinosteroids are hormones that mediate effects of light 811 37.5 How Do Photoreceptors Participate in Plant Growth Regulation? 812 Phytochromes mediate the effects of red and far-red light 812 Phytochromes have many effects on plant growth and development 813 Multiple phytochromes have different developmental roles 813 Cryptochromes, phototropins, and zeaxanthin are blue-light receptors 814