PLANTS UBER ALLES (Plants as control freaks) 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 proposition-1880 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)