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PLANT HORMONE PLANTS UBER ALLES (Plants as control freaks) OUTLINE • History and Scientists involved • Control Systems in plants and animals • Differences between plant and animal hormones • Hormone action • Plant Hormone and effects • Experimental Evidence Scientists and History of Plant Hormones • Charles and Francis Darwin – initial proposition1880 • Boysen- Jensen – 1910 • Went-1930 • Skoog-1950 • Kurosawa-1920 • Addicott-US,Wareing-England • Various fruit growers – 1960’s • Australian Scientists - 2005 + CONTROL SYSTEMS • Necessary for response to stimuli • Nervous system in animals • Tropic response systems in plants and some invertebrates • Hormonal systems in both plants and animals • Endocrine • Exocrine • Hormonal mimics Differences between Plant and animal Hormones • Animal hormones produced by specific glands and/or cells. • Plant hormones are produced by specific regions – ie. Meristems, cambriums ets. • Most animal hormones are transported in some way via blood or by ducts • Plant hormones generally must diffuse into adjacent cells or are carried by phloem Hormonal Action • Most hormones act by way of the second messenger theory. This states that the hormone binds with a receptor in the cell membrane which then triggers an induction of chemical reactions causing specific protein to form HORMONAL ACTION • Once induction has occurred, this frequently sets up a cascade effect which triggers other responses. Ie. Giberillins initiate water uptake in seeds which then causes a multitude of other responses such as production of amylase • These effects are slow to act but long lasting in permanent changes. Plant Hormones • • • • • • • • Auxins Cytokinins Giberillins Abscissic Acid Ethylene Florigen Artificial mimics Strigolactones Auxins • Growth of apical meristem and supression of lateral meristem • Cellular eleongation in grass and herbs • Differentiation of Vascular Tissue • Fruit Development and parthenocarpy • Wound repair and development of adventitious roots • Calcium release – promotes activation of calmodulin – control of calcium receptors Cytokinins • Stimulate cell division • Organogenesis in connection with auxins • High cytokinin/auxin rations favor stem and leaf development • Low rations favor root development • Senescence and programmed death of cells –longer shelf life of vegetable in grocery stores Giberillins • Rapid , Extensive growth of intact plants • Seed germination and removal of inhibitions • Juvenile characteristics • Increase of fruit size in seedless varieties • Foolish seedling disease Ethylene • Fruit Ripening –one rotten apple spoils the bushel • Flowering inhibited in most plants – exception Bromeliads • Sex expression in diecious plants – holly • Abscission – initiates break down of middle lamella at leaf /stem juncture Abscissic Acid • Closes stoma in drought conditions • Creates dormancy in seeds and buds • Formation of abscissic layer in leaves causing death and drop of leaf • Counteracts stimulatory effects of other hormones Florigen • Stimulates flowering • Has been proven to exist but has never been isolated • Experiments with long day and short day plants Strigolactones • Stimulates mycorrhizial fungal attachment to roots • Stimulates formation of lateral buds(Fibionacci numbers) • Helps seeds break dormancy after fire (Australian Fire Ecology) Plant Responses to Disease, Infection and Wounds • Types of Response • 1. Structural – isolate disease by creating hard tissue • 2. Chemical – release of antichemical infection • 1. Example Cankers and Galls – • 3. Symbiotic relationships • 3. Virus and Chestnut blight • 2. American Chestnut and Chestnut Blight Plant Responses to Environmental Factors • 1. Geotropism • 2.Phototropism • a. Daily rotation • b. Seasonal • 1. Day Neutral • 2. Long Day • 3. Short Day • 3.Thigmotropisms Ghosts of Evolution • Plants that produce fruit do so to encourage distribution away from parent plant. This avoids competition of young for nutrients and space with parent plant. Therefore all plants that have fruit have a dispersal partner Ghosts of Evolution -2 • What happens to a plant if the dispersal partner disappears, becomes extinct or decreases in numbers? • Avocado • Martynia – Unicorn Plant
