PLANT GROWTH REGULATORS General plant hormones Auxin Auxin Auxins
Linn, Demian, Executive Producer – GameVideos/1up has reference to this Academic Journal, PHwiki organized this Journal PLANT GROWTH REGULATORS THE FOLLOWING POWERPOINT PRESENTATION IS BASED, IN PART, ON MATERIAL ACCESSED ON THE INTERNET (4-12-06) http://styx.nsci.plu.edu/~dhansen/hormones2.ppt 257,2,Processes in growth http://www.coe.unt.edu/ubms/documents/classnotes/Spring2006/Plant%20Sensory%20Systems%201720-Chapter-40-2005.ppt Plant Growth Regulators AKA Plant Hormones Plant Growth Regulators – control growth, development in addition to movement PLANT GROWTH REGULATORS (PLANT HORMONES) Internal in addition to external signals that regulate plant growth are mediated, at least in part, by plant growth-regulating substances, or hormones (from the Greek word hormaein, meaning “to excite”). Plant hormones differ from animal hormones in that: No evidence that the fundamental actions of plant in addition to animal hormones are the same. Unlike animal hormones, plant hormones are not made in tissues specialized as long as hormone production. (e.g., sex hormones made in the gonads, human growth hormone – pituitary gl in addition to ) Unlike animal hormones, plant hormones do not have definite target areas (e.g., auxins can stimulate adventitious root development in a cut shoot, or shoot elongation or apical dominance, or differentiation of vascular tissue, etc.).
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PLANT GROWTH REGULATORS PLANT GROWTH REGULATORS ARE NECESSARY FOR, BUT DO NOT CONTROL, MANY ASPECTS OF PLANT GROWTH AND DEVELOPMENT. – BETTER NAME IS GROWTH REGULATOR. THE EFFECT ON PLANT PHYSIOLOGY IS DEPENDENT ON THE AMOUNT OF HORMONE PRESENT AND TISSUE SENSITIVITY TO THE PLANT GROWTH REGULATOR substances produced in small quantities by a plant, in addition to then transported elsewhere as long as use have capacity to stimulate in addition to /or inhibit physiological processes at least five major plant hormones or plant growth regulators: auxins, cytokinins, gibberellins, ethylene in addition to abscisic acid General plant hormones Auxins (cell elongation) Gibberellins (cell elongation + cell division – translated into growth) Cytokinins (cell division + inhibits senescence) Abscisic acid (abscission of leaves in addition to fruits + dormancy induction of buds in addition to seeds) Ethylene (promotes senescence, epinasty, in addition to fruit ripening) EARLY EXPERIMENTS ON PHOTROPISM SHOWED THAT A STIMULUS (LIGHT) RELEASED CHEMICALS THAT INFLUENCED GROWTH Results on growth of coleoptiles of canary grass in addition to oats suggested that the reception of light in the tip of the shoot stimulated a bending toward light source.
Auxin Auxin increases the plasticity of plant cell walls in addition to is involved in stem elongation. Arpad Paál (1919) – Asymmetrical placement of cut tips on coleoptiles resulted in a bending of the coleoptile away from the side onto which the tips were placed (response mimicked the response seen in phototropism). Frits Went (1926) determined auxin enhanced cell elongation. Demonstration of transported chemical Auxin Discovered as substance associated with phototropic response. Occurs in very low concentrations. Isolated from human urine, (40mg 33 gals-1) In coleoptiles (1g 20,000 tons-1) Differential response depending on dose.
Auxins Auxin Auxin promotes activity of the vascular cambium in addition to vascular tissues. plays key role in fruit development Cell Elongation: Acid growth hypothesis auxin works by causing responsive cells to actively transport hydrogen ions from the cytoplasm into the cell wall space Signal-transduction pathways in plants Auxin interacts with calcium ions which in turn calmodulin, a protein, which regulates many processes in plants, animals, in addition to microbes.
Loosening of cell wall Polar transport of Auxin Auxin Synthetic auxins widely used in agriculture in addition to horticulture prevent leaf abscission prevent fruit drop promote flowering in addition to fruiting control weeds Agent Orange – 1:1 ratio of 2,4-D in addition to 2,4,5-T used to defoliate trees in Vietnam War. Dioxin usually contaminates 2,4,5-T, which is linked to miscarriages, birth defects,leukemia, in addition to other types of cancer.
Additional responses to auxin abscission – loss of leaves flower initiation sex determination fruit development apical dominance Control of abscission by auxin Apical Dominance Lateral branch growth are inhibited near the shoot apex, but less so farther from the tip. Apical dominance is disrupted in some plants by removing the shoot tip, causing the plant to become bushy.
Gibberellin Discovered in association with In 1930’s, bakanae or foolish seedling disease of rice (Gibberella fujikuroi) In 1930’s, Ewiti Kurosawa in addition to colleagues were studying plants suffering from bakanae, or “foolish seedling” disease in rice. Disease caused by fungus called, Gibberella fujikuroi, which was stimulating cell elongation in addition to division. Compound secreted by fungus could cause bakanae disease in uninfected plants. Kurosawa named this compound gibberellin. Gibberella fujikuroi also causes stalk rot in corn, sorghum in addition to other plants. Secondary metabolites produced by the fungus include mycotoxins, like fumonisin, which when ingested by horses can cause equine leukoencephalomalacia – necrotic brain or crazy horse or hole in the head disease. Fumonisin is considered to be a carcinogen. Gibberellins Gibberellins are named after the fungus Gibberella fujikuroi which causes rice plants to grow abnormally tall. synthesized in apical portions of stems in addition to roots important effects on stem elongation in some cases, hastens seed germination
Effects of Gibberellins Cell elongation. GA induces cellular division in addition to cellular elongation; auxin induces cellular elongation alone. GA-stimulated elongation does not involve the cell wall acidification characteristic of auxin-induced elongation Breaking of dormancy in buds in addition to seeds. Seed Germination – Especially in cereal grasses, like barley. Not necessarily as critical in dicot seeds. Promotion of flowering. Transport is non-polar, bidirectional producing general responses. Gibberellins in addition to Fruit Size Fruit Formation – “Thompson Seedless” grapes grown in Cali as long as nia are treated with GA to increase size in addition to decrease packing. Wild Radish Rosette & Bolt YEAR ONE YEAR ONE A FLOWERING ANNUAL
Common Mullen Rosette & Bolt YEAR ONE YEAR TWO A FLOWERING BIENNIAL Mobilization of reserves Cytokinins
Discovery of cytokinins Gottlieb Haberl in addition to t in 1913 reported an unknown compound that stimulated cellular division. In the 1940s, Johannes van Overbeek, noted that plant embryos grew faster when they were supplied with coconut milk (liquid endosperm), which is rich in nucleic acids. In the 1950s, Folke Skoog in addition to Carlos Miller studying the influence of auxin on the growth of tobacco in tissue culture. When auxin was added to artificial medium, the cells enlarged but did not divide. Miller took herring-sperm DNA. Miller knew of Overbeek’s work, in addition to decided to add this to the culture medium, the tobacco cells started dividing. He repeated this experiment with fresh herring-sperm DNA, but the results were not repeated. Only old DNA seemed to work. Miller later discovered that adding the purine base of DNA (adenine) would cause the cells to divide. Adenine or adenine-like compounds induce cell division in plant tissue culture. Miller, Skoog in addition to their coworkers isolated the growth facto responsible as long as cellular division from a DNA preparation calling it kinetin which belongs to a class of compounds called cytokinins. In 1964, the first naturally occurring cytokinin was isolated from corn called zeatin. Zeatin in addition to zeatin riboside are found in coconut milk. All cytokinins (artificial or natural) are chemically similar to adenine. Cytokinins move nonpolarly in xylem, phloem, in addition to parenchyma cells. Cytokinins are found in angiosperms, gymnosperms, mosses, in addition to ferns. In angiosperms, cytokinins are produced in the roots, seeds, fruits, in addition to young leaves Function of cytokinins Promotes cell division. Morphogenesis. Lateral bud development. Delay of senescence. Cytokinins Cytokinins, in combination with auxin, stimulate cell division in addition to differentiation. most cytokinin produced in root apical meristems in addition to transported throughout plant inhibit as long as mation of lateral roots auxins promote their as long as mation
Circadian Clocks Circadian clocks are endogenous timekeepers that keep plant responses synchronized with the environment. circadian rhythm characteristics must continue to run in absence of external inputs must be about 24 hours in duration can be reset or entrained (to determine or modify the phase or period of
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