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9.3 plant growth

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9.3 plant growth

  1. 1. Essential idea: Plants adapt their growth to environmental conditions. 9.3: Plant Growth
  2. 2. Understandings Statement Guidance 9.3 U.1 Undifferentiated cells in the meristems of plants allow indeterminate growth. 9.3 U.2 Mitosis and cell division in the shoot apex provide cells needed for extension of the stem and development of leaves. 9.3 U.3 Plant hormones control growth in the shoot apex 9.3 U.4 Plant shoots respond to the environment by tropisms. 9.3 U.5 Auxin efflux pumps can set up concentration gradients of auxin in plant tissue. 9.3 U.6 Auxin influences cell growth rates by changing the pattern of gene expression.
  3. 3. Applications and Skills Statement Guidance 9.3 A.1 Application: Micropropagation of plants using tissue from the shoot apex, nutrient agar gels and growth hormones. 9.3 A.2 Application: Use of micropropagation for rapid bulking up of new varieties, production of virus-free strains of existing varieties and propagation of orchids and other rare species.
  4. 4. Dicotyledon Structure 1. Root system extracts minerals (nitrates & phosphates) along with water from the soil. The main root has lateral divisions that are either shallow or deep depending on the water availability of water. 2. Stem structure supports leaf and contains the vascular tissue that transports substances around the plant. 3. Petioles divisions of the stem. They support the leaf and contains branches of the vascular tissues. www.click4biology.com
  5. 5. 4. Leaf large surface area to absorb light energy for photosynthesis. Concentrated within the palisade tissue of the leaf is chlorophyll to absorb the photons of light. 5. Auxiliary bud provide the tissues for the growth of lateral branches in future growing seasons. 6. Terminal bud contains the structures for the growth and elongation of the main stem. www.click4biology.com
  6. 6. Dicotyledonous stem Tissue types of the plant stem: • Epidermis: surface of the stem made of a number of layers often with a waxy cuticle to reduce water loss. • Cortex Tissue: Forming a cylinder of tissue around the outer edge of the stem. Often contains cells with secondary thickening in the cell walls which provides additional support. • Vascular bundle: contains xylem, phloem and cambium tissue. www.click4biology.com
  7. 7. Dicotyledonous stem • Xylem: a longitudinal set of tubes that conduct water from the roots upward through the stem to the leaves. • Phloem (sieve elements) transports sap through the plant tissue in a number of possible directions. • Vascular cambium is a type of lateral meristem that forms a vertical cylinder in the stem. The cambium produces the secondary xylem and phloem through cell division in the vertical plane. • In the center of the stem can be found the pith tissue composed of thin walled cells called parenchyma. In some plants this section can degenerate to leave a hollow stem www.click4biology.com
  8. 8. 9.3 U.1 Undifferentiated cells in the meristems of plants allow indeterminate growth. • Plants growth is restricted to 'embryonic' regions called meristems. Having specific regions for growth and development (restricted to just the meristematic tissue). • Meristems composed of undifferentiated cells that are undergoing active cell division Growth Occurs: • Terminal & Axillary buds • Tap and Lateral roots • Cambium (stem thickness) www.click4biology.com
  9. 9. 9.3.U.1 Undifferentiated cells in the meristems of plants allow indeterminate growth. • Apical Meristems – found at the tips of stems and roots • Lateral Meristems – responsible for thickness of the stems Apical meristem www.click4biology.com
  10. 10. • Auxins (hormone) – initiating the growth of roots, influencing the development of fruits and regulating leaf development. • Auxin influences cell division growth rates and patterns. • Auxins also influence cell elongation. (a) Shoot apical meristem (b) Leaf primordial (c) Auxiliary bud primordium (d) leaf (e) Stem tissue http://www.geraniumsonline.com/apex1.jpg Apical meristem at the top of the plant 9.3.U.1 Undifferentiated cells in the meristems of plants allow indeterminate growth. 9.3.U.6 Auxin influences cell growth rates by changing the pattern of gene expression
  11. 11. Root apical meristem: (a) Root cap. (b) Root apical meristem. (c) Ground meristem. (d) Protoderm. (e) Epidermal tissue of the root. (f) Vascular tissue (central stele). Apical Meristem www.click4biology.com 9.3.U.1 Undifferentiated cells in the meristems of plants allow indeterminate growth. 9.3.U.6 Auxin influences cell growth rates by changing the pattern of gene expression Apical meristem at the root of the plant
  12. 12. Apical meristem : Axillary Bud Growth • Stem differentiation at the apical meristem creates branching. • The diagram illustrate that the tissue added at the apical meristem differentiates into the various primary plant body structure (AB) www.click4biology.com 9.3.U.1 Undifferentiated cells in the meristems of plants allow indeterminate growth. 9.3.U.6 Auxin influences cell growth rates by changing the pattern of gene expression
  13. 13. 1. Cambium that produces secondary xylem and phloem 2. Cork cambium produces some of the bark layer of a stem. *secondary growth adding thickness usually in the following years in a perennial plant. www.click4biology.com 9.3.U.1 Undifferentiated cells in the meristems of plants allow indeterminate growth. 9.3.U.6 Auxin influences cell growth rates by changing the pattern of gene expression Lateral meristem is secondary growth
  14. 14. • Cells in meristems are small, therefore they go through the cycle quicker to produce more cells through mitosis and cytokinesis • These new cell absorb nutrients and water which increase their volume & mass http://www.navitar.com/images/bf2.jpg 9.3 U.2 Mitosis and cell division in the shoot apex provide cells needed for extension of the stem and development of leaves.
  15. 15. PLANT GROWTH REGULATORS (aka PLANT HORMONES)PLANT GROWTH REGULATORS (aka PLANT HORMONES) Plant hormones differ from animal hormones in that:  Unlike animal hormones, plant hormones are not made in tissues specialized for hormone production. (e.g., sex hormones made in the gonads, human growth hormone - pituitary gland)  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.).  There a several hormones found in plants. Auxins. Auxins (cell elongation), GibberellinsGibberellins (cell elongation + cell division), CytokininsCytokinins (cell division), Abscisic acidAbscisic acid (Controls guard cells) and EthyleneEthylene (promotes fruit ripening) 9.3 U.3 Plant hormones control growth in the shoot apex.
  16. 16. Cytokinins •Hormones that stimulate cell division, leaf aging (leaf senescence) and leaf enlargement •Cytokinins, in combination with auxin, stimulate cell division and differentiation. •Produced in roots and travel upward in xylem sap. *The hormone has no direct effect on the cell wall. For this reason it work best with the plant hormone Auxin The plant, below left has been genetic modification to increase levels of cytokinin Nicotiana (Solanaceae family)
  17. 17. Increasing auxin concentration Increasing Cytokinin concentration Cytokinin and auxin interactions Callus of Nicotiana (Solanaceae family)
  18. 18. Auxin • Increases the flexibility of the cell wall. A more flexible wall will stretch more as the cell is actively growing. • Auxin accumulates in the apical meristem. Allows selective cell elongation. • By interacting with other hormones, Auxin also induces cell width .
  19. 19. Acid Growth hypothesis• Plant cell growth dependent on the growth hormone auxin. • Auxin activates a plasma membrane proton pump, which acidifies the cell wall. • The lower pH, in turn, activates growth-specific enzymes that hydrolyze the bonds holding to cellulose. Breaking of these bonds results in the loosening of the cell wall. Causes uptake of water – which leads to a passive increase in cell size. Loosening of cell wallLoosening of cell wall
  20. 20. Enzymes break the bonds holding xyloglucan to cellulose. Enzymes break the xyloglucan molecules. Other enzymes break the pectin Molecules (NOT SHOWN). From: Biochemistry and Molecular Biology of plants The cell is now free to expand in a given direction.
  21. 21. When expansion has stopped: From: Biochemistry and Molecular Biology of plants Cell wall proteins lock the cells new shape as these new wall components are being made. Enzymes form new xyloglucan Molecules which re-attach to the Cellulose microfibrils. Also form New cross-links with newly formed Cellulose microfibrils.
  22. 22. For a plant to grow: •new wall material has to be laid down as the cell expands New cellulose microfibrils are made as the cell expands. Plasma membrane These line up perpendicular to the direction of growth. As this happens the existing wall has to be loosened. From: Biochemistry and Molecular Biology of plants
  23. 23. • Darwin’s studied the of effects auxin on movement. • Darwin studied phototropism using the germinating stem of the canary grass. • The cylindrical shoot is enclosed in a sheath of cells called the coleoptile. http://semoneapbiofinalexamreview.wikispaces.com/file/view/39_05bColeoptileDarwins-L.jpg/289955863/560x411/39_05bColeoptileDarwins-L.jpg 9.3 A.1: Micropropagation of plants using tissue from the shoot apex, nutrient agar gels and growth hormones.
  24. 24. 9.3 A.1: Micropropagation of plants using tissue from the shoot apex, nutrient agar gels and growth hormones. Auxin was first isolated by F. W. Went (m) Went isolated the growth medium auxin onto agar gel. (n) The gel was cut up into block as a way of quantifying the dose of auxin used. (o) The agar block (containing auxin) are placed asymmetrically on the stem. (p) The angle of bending-growth was measured http://plantphys.info/plant_physiology/images/paaltip.gif
  25. 25. 9.3 A.1: Micropropagation of plants using tissue from the shoot apex, nutrient agar gels and growth hormones. • Since Auxin (IAA3) was synthetically produced more rigorous quantitative bio-assay can be performed • This graph measures the bending- growth against the concentration of IAA3. Graph suggests: • Increasing IAA3 increases the bending- growth angle. • Optimal angle of bending-growth is achieved between 0.2- 0.25 mg • Higher levels seem to have reduced- bending growth
  26. 26. Tropisms: External Factors that Regulate Plant Development • a change in the growth pattern or movement of a plant in response to an external stimulus that mainly come from one direction. • As tropisms effect the growth pattern of plants, they greatly effect the plant cell wall. Best known: Phototropism Induces cells AWAY from light to elongate. Cell wall expands in a specific direction. 9.3 U.4 Plant shoots respond to the environment by tropisms.
  27. 27. Phototropism •Phototropism is the growth of stems of plants toward light - it is probably the best known of the plant tropisms - phototropism is caused by elongation of the cells on the shaded part of the plant - so that entire plant bends or curves toward the light •This growth pattern is caused by the hormone auxin - auxin migrates to the shaded part of the plant and stimulates increased cell growth and elongation on the shaded part of the plant IAA = Auxin 9.3 U.4 Plant shoots respond to the environment by tropisms.
  28. 28. http://upload.wikimedia.org/wikipedia/commons/8/8d/Sunflower_Field_near_Raichur,_India.jpg
  29. 29. http://upload.wikimedia.org/wikipedia/commons/thumb/4/4f/Museo_Larreta_Yatay.jpg/1280px-Museo_Larreta_Yatay.jpg
  30. 30. Gravitropism: Response of a plant to gravity. Causes roots to grow downwards and stems to grow upwards. This response is governed by Auxin. Auxin builds up in the cells of the upper surface of root This induces localized cell elongation and re-orientation of the cell walls to allow the root to grow downwards. 9.3 U.5: Auxin efflux pumps can set up concentration gradients of auxin in plant tissue.
  31. 31. Gravitropism = GeotropismGravitropism = Geotropism http://gp1.wac.edgecastcdn.net/802892/production_public/Artist/150029/image/Gravitropism_pos.jpg
  32. 32. Gravitropism in plants
  33. 33. 9.3.A.2 Use of micropropagation for rapid bulking up of new varieties, production of virus-free strains of existing varieties and propagation of orchids and other rare species. • Stock plant is identified for a desirable feature. • Micropropagation depends on totipotent cells which retain the ability to differentiate. • Tissue from the stock plant are sterilized and cut into pieces called explant. • The explant is placed into a growth media along with plant hormones. This undifferentiate mass is called a callus. • Once roots and shoots are developed the cloned plant can be transferred to soil. • This technique is used to overcome plant viruses or to produce large numbers of rare plants. http://www.toptenz.net/wp-content/uploads/2012/04/ghostorchid-570x427.jpg
  34. 34. 9.3 A.2 Use of micropropagation for rapid bulking up of new varieties, production of virus-free strains of existing varieties and propagation of orchids and other rare species. Sugar Cain http://www.sciencephoto.com/image/212210/350wm/G28002 82Cereal_plants_being_grown_from_tissue_culture-SPL.jpg http://php.med.unsw.edu.au/cellbiology/images/6/6e/Plant_Tis sue_Culture_Lab.jpg
  35. 35. 9.3 A.2 Use of micropropagation for rapid bulking up of new varieties, production of virus-free strains of existing varieties and propagation of orchids and other rare species. Sugar Cain http://vsisugar.com/gallery/tissueculture-gallery/img/photo15.jpghttp://3.imimg.com/data3/IQ/AA/WSITE-5570267/files-resized- 199442-470-353-aebeec90aa3a60f977156f626701cf17c8bb5439- 250x250.jpg

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