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Transcript
Control Systems in Plants Chapter 22 Plant Hormones Chemical messengers in plants which control: 1. germination 2. growth 3. flowering 4. fruit production Five Major Plant Hormones 1. Auxins—promotes plant growth; produced in the apical meristems at the tips of shoots 2. Cytokinins—stimulate cell division; produced in actively growing tissues such as embryos, roots, and fruits; slows the aging of flowers and fruit; promote cell division in axillary buds 3. Giberellins—produced at the tips of both stems and roots; stimulate growth of stems; also promote seed germination in some species 4. Abscisic Acid—inhibits cell division in buds and in the vascular cambium during periods of dormancy; promotes dormancy in seeds; acts as a stress hormone causing stomata to close 5. Ethylene—stimulates fruit ripening Plants Respond to Changes in Environment TropismsA. Thigmotropism—response to touch B. Phototropism—response to light C. Gravitropism—response to gravity Coping with Stressful Environments 1. Drought— a. Close stomata b. Cacti store water in fleshy stems; their leaves are modified to spines c. Succulents have a thick cuticle; their green stems are the main photosynthetic organs 2. Flooding—plants that are in flooded conditions release ethylene; some cells in the roots are killed creating air tubes which act as snorkels Mangrove trees have roots that are partially above ground. 3. Salt Stress—When salt builds up in the soil, roots can lose their water through osmosis Halophytes—have salt glands that pump salt out of the plant across the leaf epidermis Pickleweed pumps salt to the stems at the tips of the plant, then sheds its stems Plant Defenses 1. Epidermis—first line of defense against disease 2. Chemicals—second line of defense a. Some are microbial b. Some signal lignin production to harden cell walls around the infected area 3. Inherited ability to recognize and attack pathogens 4. Thorns, chemical poisons—defend against being eaten