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Plant Orientation Responses

Plant Orientation Responses. Introductory video. http://www.youtube.com/watch?v=zctM_TWg5Ik ( Plant Physiology: Phototropic Response). Biozone p166 together!. Tropisms and Growth responses.

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Plant Orientation Responses

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  1. Plant Orientation Responses

  2. Introductory video • http://www.youtube.com/watch?v=zctM_TWg5Ik(Plant Physiology: Phototropic Response). • Biozone p166 together!

  3. Tropisms and Growth responses • Tropisms are plant responses to external stimuli, where the stimulus direction determines the direction of the growth response. • They can be positive or negative. • Nastic Responses are non directional responses to intensity of a stimulus. • They are not described as positive or negative • E.g. Venus fly trap, opening/ closing of stomata. • Biozone p170

  4. Hormones • The ways in which a plant responds to stimuli is coordinated by hormones. • . Hormones also control the growth of a plant • One plant hormone is called auxin (indole acetic acid or IAA). • Auxin is made by cells in the tips of the roots and shoots. • It speeds up growth in shoots and slows down growth in roots. • Unequal distribution of hormones causes unequal growth rates in different tissues.

  5. How Phototropism works. Coleoptile- A protective sheath enclosing the first leaf shoot (plumule) of a seedling. http://www.cartage.org.lb/en/themes/Sciences/BotanicalSciences/PlantHormones/Nutrition/3224.GIF

  6. Phototropism mechanism. 1. Auxin(IAA) is produced in the tips of shoots. (made in actively growing plant tissue (meristematic) from the a.a tryptophan. 2. If light is shone from one side of the seedling, the auxin migrates down from the tip and concentrates on the darker side of the seedling. 3. The greater concentration of auxin on the dark side, promotes greater cell elongation on this side. So the cells grow faster and longer than the cells on the bright side. The shoot bends towards the light as a result of this uneven distribution of auxin and hence uneven growth of the shoot.

  7. http://plantphys.info/plant_physiology/images/darwintip.gif

  8. Experimental findings • The auxin is produced in the tip of shoots. • It is water soluble and diffuses through agar or gelatine blocks, but will not pass through mica. • The auxin causes elongation of the cells, thus promoting upwards growth. • Shoots bend towards light.

  9. Geotropism- How does it work? http://images.google.co.nz/imgres?imgurl=http://lgfl.skoool.co.uk/uploadedImages/Coord10.14_geotropism.gif&imgrefurl=http://lgfl.skoool.co.uk/examcentre.aspx%3Fid%3D221&usg=__39UBvOkahZwkgPdJO9PGk4KOnE4=&h=220&w=440&sz=12&hl=en&start=4&tbnid=K0isqmL35T4BKM:&tbnh=64&tbnw=127&prev=/images%3Fq%3Dgeotropish%26gbv%3D2%26hl%3Den

  10. http://www.cartage.org.lb/en/themes/sciences/botanicalsciences/PlantHormones/PlantHormones/gravitrop.gifhttp://www.cartage.org.lb/en/themes/sciences/botanicalsciences/PlantHormones/PlantHormones/gravitrop.gif

  11. Activity • Write a detailed explanation of why shoots show negative gravitropism and roots show positive gravitropism. You can include an annotated diagram if you wish. • Biozone p167-169.

  12. Other tropisms • Chemotropism –e.g. growth of pollen tube towards ovary. • Hydrotropism -strong response • Thigmotropism-which side is growth inhibited or slowed down in ? • Self check p17-18 green book

  13. Effect of auxin on shoots/ roots • This depends on the concentration in auxin. • Low concentrations stimulate roots, while high concentrations inhibit (and can kill). • Low concentrations stimulate the growth of lateral buds, while high concentrations inhibit. • Low concentrations do not stimulate the stems, while high concentrations do.

  14. Apical dominance The process that causes the triangular shape of trees like conifers. • Auxin is in high concentrations at the top of the plant. This stimulates shoot and inhibits growth in lateral buds. • Lower down the auxin in less concentrated and also deactivated by some enzymes. Cytokinins also stimulate lateral buds, causing bushiness of shrubs near bottom. • Principle can also be used in broad leaf trees. http://www.cactus-art.biz/note-book/Dictionary/aaa_Dictionary_pictures/Apical_and_axillary_bud.jpg

  15. Etiolation • Occurs when plants are grown in reduced light or the dark. • Leaves are small and yellow and there are long internodes. • Phytochlorophyll  turns to green chlorophyll. http://biology.uwsp.edu/courses/botlab/images/Lab12Growth/12D%20etiolation%20corn.JPG

  16. Plant Hormones and Applications Plant hormones are called phytohormones. • Gibberellins –produced in growing tips –cause rapid elongation of stem. Can promote germination and stem thickening. • Cytokinins – stimulate cell division in tissue cultures and whole plants. Proportion with auxin can determine what grows in tissue cultures. (Page 19 green book) • Ethylene gas (ethene)-ripening. http://www.crossrefrigeration.com/images/bananaripe1_14.jpg

  17. Abscisic acid ABA- • close stomata and reduce water loss. Inhibiting hormone against auxin, gibberellins and cytokinins. • Prepares deciduous plants for leaf fall. • Helps induce winter dormancy.

  18. Other effects of auxin (IAA) • Rooting powders for cuttings. • Suppression of root elongation. • Suppression of lateral buds (apical dominance) • Stimulation of mitosis in stems of woody plants. • Initiation of flowering in some plants. • Prevention of premature abscission (dropping) of leaves and fruit. (fruit growers)

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