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Plant Hormones

Plant Hormones. Plant Hormones. There are five major types of plant hormones: Gibberelins Cytokinins Ethylene Abcisic Acid Auxins The structure and function of each type of hormone will be described. Gibberellins. Overview. Gibberellins (GAs) regulate and influence: cell elongation

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Plant Hormones

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  1. Plant Hormones

  2. Plant Hormones • There are five major types of plant hormones: • Gibberelins • Cytokinins • Ethylene • Abcisic Acid • Auxins • The structure and function of each type of hormone will be described

  3. Gibberellins

  4. Overview • Gibberellins (GAs) regulate and influence: • cell elongation • seed germination • dormancy • flowering • sex expression • enzyme induction • leaf and fruit senescence.

  5. Germination Signal starch hydrolysis through inducing the synthesis of the enzyme α-amylase in the aleurone cells Gibberellins produced in the scutellum diffuse to the aleurone cells where they stimulate the secretion α-amylase α-Amylase then hydrolyses starch into glucose Gibberellins cause higher levels of transcription of the gene coding for the α-amylase enzyme

  6. Gibberellins: Chemical Structure • Gibberelins have complex ring structures • Typically contain carboxylic acid groups • Many specific gibberelins exist • Numeric naming system (i.e. GA#) • May be classified into two structural types: • C-19 Gibberelins (19 carbon) • C-20 Gibberelins (20 carbon)

  7. Gibberellins: Chemical Structure • Type 1: 19 Carbon Gibberelins

  8. Gibberellins: Chemical Structure • Type 2: 20 Carbon Gibberelins

  9. Cytokinins

  10. Cytokinins • Found in a variety of plants and have many functions • Synthesized in meristematic tissues in roots and transported to aboveground organs • Regulate growth and development of tissue primarily by promoting cell division • Involved in germination, shoot differentiation, leaf senescence • Interacts with other plant hormones for some functions

  11. Cytokinins Function • Regulates apical dominance and lateral root initiation • Slows down senescence (plant aging) and chlorophyll degradation in aging leaves • Regulates growth of dicot seedlings in the dark (in combination with ethylene) • Involved in development of sex organs and male sterility • Synthesized in meristematic tissues in roots and transported to aboveground organs

  12. Cytokinins • Cytokinins contain adenine: Two structure types: • Isoprenoid • Isoprene structural units: • Aromatic • Contain aromatic groups

  13. Cytokinins: Isoprenoid Isoprene units adenine

  14. Cytokinins: Aromatic adenine Aromatic group

  15. Cytokinins: Aromatic Aromatic group adenine

  16. Ethylene

  17. Ethylene • Universally produced by all plants • Angiosperms, Gymnosperms, Ferns, Mosses, Liverworts • Also found in some fungi, yeast and bacteria • Important roles in: • Abscission • Germination • Senescence • Stress • response to pathogens

  18. Ethylene and Fruit Ripening • Helps fruits go through color change, softening of walls, conversion of starch to sugar • Ethylene is produced in low amounts throughout plant life • some “climacteric” plants have sudden peaks in ethylene synthesis which signals ripening changes • Ethylene gas is sprayed on fruit crops to ripen at same time

  19. Ethylene and Stress • Some stress situations trigger ethylene production • exposure to heat/cold • physical damage • attack by fungal or bacterial pathogens • flooding that limits oxygen • Similar to Abscisic acid’s stress response

  20. Growth and Messaging • Ethylene and growth • Promotes root growth and root hair growth • Can cause asymmetric growth in stems and leaves • Ethylene regulates seedlings’ horizontal growth & apical hook formation…= “Triple response” of seedlings grown in dark • Can act as second messenger • Auxin, cytokinin can cause ethylene production in seedlings

  21. Ethylene’s “triple response” Apical hook formation

  22. Ethylene: Chemical Structure • Ethylene is a very small, simple molecule compared to other plant hormones • Two carbons sharing a double bond • Ethylene is a gas at room temperature

  23. Abscisic Acid

  24. Abscisic Acid (ABA) Found universally in plants and algae Many functions! Important roles in: plant development bud & seed dormancy Germination cell division leaf senescence Abscission cellular response to stress

  25. Abscisic Acid • Acts as a general inhibitor of growth and metabolism • Inhibits growth in hypocotyls, epicotyls, leaves, coleoptiles • Seed dormancy • ABA promotes seed dormancy so plant seeds can withstand desiccation

  26. ABA as a Stress Hormone • ABA increases with various environmental or biological plant stresses • Excess heat, pests, excess salt and/or dehydration • Wilted plants have high levels of ABA • In a drought, ABA increases in some plants, causing the stomata to close, preventing water loss • ABA can also produces osmolytes that protect cell membranes from dehydration

  27. Abscisic Acid Chemical Structure • Abscisic acid is a carboxylic acid Carboxylic acid

  28. Auxins

  29. It’s All in the Name “Auxins” from the Greek word αυξανω = "I grow or increase". They were the first of the major plant hormones to be discovered.

  30. Overview essential for cell growth affects both cell division and cellular expansion. may promote axial elongation (as in shoots), lateral expansion (as in root swelling), or isodiametric expansion (as in fruit growth) auxin-promoted cellular expansion occurs in the absence of cell division. auxin-promoted cell division and cell expansion may be closely sequenced within the same tissue (root initiation, fruit growth)

  31. Important Functions coordination of many growth and behavioral processes in the plant life cycle stimulate or inhibit the expression of specific genes. coordinate development at all levels in plants, from the cellular level through organs and ultimately the whole plant.

  32. Master Hormone indole-3-acetic acid (IAA). the most important member of the auxin family the most potent native auxin generates the majority of auxin effects in intact plants

  33. Working Together patterns of active transport are complex typically act in concert with, or in opposition to other plant hormones auxins and other plant hormones nearly always interact to determine patterns of plant development.

  34. Auxin Shared Functions stimulates cell elongation by stimulating wall loosening factors, such as elastins, to loosen cell walls (with gibberellins) stimulates cell division (with cytokinins) applied to callus, rooting can be generated (with cytokinin) xylem tissues can be generated (with cytokinins)

  35. More Auxin Shared Functions promotes femaleness in dioecious flowers (with ethylene) inhibits or promotes leaf and fruit abscission (with ethylene) stimulate cell division in the cambium andin tissue culture (with cytokinins)

  36. Auxin Functions Stimulate cell elongation stimulate differentiation of phloem and xylem Stimulate root initiation on stem cuttings and lateral root development in tissue culture mediate the tropistic response of bending in response to gravity and light suppresses growth of lateral buds delay leaf senescence

  37. More Auxin Functions can induce fruit setting and growth in some plants involved in assimilate movement toward auxin, possibly by an effect on phloem transport delay fruit ripening promote flowering in Bromeliads stimulate growth of flower parts stimulate the production of ethylene at high concentrations inhibit growth by closing the stoma during water stress.

  38. Auxins: Chemical Structure • Many naturally occurring auxins exist, along with many synthetic auxins used in agriculture • Most naturally occurring auxins contain an indole ring group or a phenyl group • Auxins (natural and synthetic) are carboxylic acids • Halides are also seen in both natural and synthetic auxins

  39. Naturally Occurring Auxins Carboxylic acid =IAA, the most important member of the auxin family

  40. Naturally Occurring Auxins

  41. Synthetic Auxins

  42. Synthetic Auxins Ether linkage halogens

  43. Sources • Wikipedia, Auxin, 2010, http://en.wikipedia.org/wiki/Auxin • Campbell, Neil A., and Jane B. Reece. Biology. 6th ed. Boston: Benjamin-Cummings Company, 2001. • Delker, C., Raschke, A. and Quint, M., 2008, Auxin dynamics: the dazzling complexity of a small molecule’s message, Planta, vol 227, 929-941. • Gibberellins: A Short History, from http://www.plant-hormones.info, the home since 2003 of a website developed by the now-closed Long Ashton Research Station • Wikipedia, Gibberellin, 2010, http://en.wikipedia.org/wiki/Gibberellin • Koning, Ross E. 1994. Auxins. Plant Physiology Information Website. http://plantphys.info/plant_physiology/auxin.shtml. (4-7-2010). • Litwak, G. 2005. Plant hormones. Elsevier Academic Press: San Diego, CA. • Raghavan, V. 1997. Molecular embryology of flowering plants. Cambridge University Press. New York, NY. • Srivastava, LM. 2002. Plant growth and development: hormones and environment. Elsevier Science: San Diego, CA. • http://www.plant-hormones.info/auxins.htm the home since 2003 of a website developed by the now-closed Long Ashton Research Station

  44. Photo credits: • http://humankinetics.files.wordpress.com/2009/07/fresh-fruit.jpg • http://www.nature.com/emboj/journal/v22/n6/thumbs/7595043f4.jpg • http://plantphys.info/plant_physiology/images/tripleresponse.gif • http://farm4.static.flickr.com/3657/3513022448_e7bb1c305e_m.jpg • http://www.hiltonpond.org/images/FreezeHackberry01.jpg

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