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Young Leaf

Young Leaf. Shoot Tip. Axillary Bud. Node. Internode. Phytomere Node Leaf Axillary Bud Internode. Increase in length of the stem occurs largely by internodal elongation. Node. Internode. Plant cells are surrounded by rigid cell walls. Cell migration does not occur in plants.

cameran-barrett
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Young Leaf

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  1. Young Leaf Shoot Tip Axillary Bud Node Internode

  2. Phytomere Node Leaf Axillary Bud Internode

  3. Increase in length of the stem occurs largely by internodal elongation. Node Internode

  4. Plant cells are surrounded by rigid cell walls. Cell migration does not occur in plants.

  5. Cell expansion plays a major role in growth Root cells expand their volume 50 times by expanding lengthwise but not widthwise

  6. In roots, cell expansion plays a major role in growth Two competing plant hormones determine the direction of cell expansion: GA (gibberellic acid) promotes growth along the length Ethylene promotes growth along the width

  7. Auxin and Cytokinin control shoot and root growth High levels of Cytokinin and low levels of Auxin promote shoot development (stems with leaves) High levels of Auxin and low levels of Cytokinin promote root development

  8. The Miller-Skoog Experiment: Cloning • Place single cell on medium with high levels of Cytokinin and low levels of Auxin to promote shoot development (stems with leaves) • Place shoots on medium with high levels of Auxin and low levels of Cytokinin to promote root development at the base of the shoot • Transfer rooted shoots to soil and grow plants to maturity

  9. Figure 38.2 Review of an idealized flower

  10. Fertilization

  11. Figure 38.10 The development of a dicot plant embryo

  12. Pollination is the first step of the fertilization process.

  13. The pollen “germinates” and grows down into the ovary where fertilization of the egg occurs.

  14. A successful fertilization will produce a fertilized egg with 2X DNA.

  15. Even at this one cell stage the embryo reveals polarity. The first cell division is asymmetric, producing a small apical cell and a larger basal cell.

  16. The apical cell will later give rise to the entire “embryo proper”. The basal cell will give rise to a small umbilical cord-like structure called the suspensor.

  17. The small apical cell divides several times to generate the globular embryo. All cells of this embryo appear morphologically similar.

  18. Several divisions later morphological asymmetry is seen in the heart shaped embryo.

  19. Arabidopsis embryogenesis

  20. Arabidopsis embryogenesis

  21. Cotyledons (seed leaves) Shoot Apical Meristem Hypocotyl (seedling stem) Root Root Apical Meristem

  22. Plant Stem Cells: Shoot and root meristem Weigel and Jürgens, 2002; Bowman and Eshed, 2000; Nakajima and Benfey, 2002

  23. What is a shoot apical meristem? -a group of undifferentiated “stem” cells -renew themselves while generating lateral organs off the flanks - located at the tips of growing shoots - 3 types:vegetative, inflorescence, floral

  24. Gerd Jurgens searched for embryo pattern mutants. • Soak seeds in a mutagen • Grow plants to maturity • These plants would be carriers of mutations (m/+) • When these carriers self-fertilize, the resulting • embryos would be: +/+, m/+, m/m • Mutants similar to gap mutants in flies, lacking regions of the embryo, including the apical structures, the stem (hypocotyl) and root, were identified

  25. Embryo Pattern Mutants

  26. Organization of the SAM Fletcher 2003

  27. L1 and L2 cells divide anticlinally: perpendicular to the surface These divisions contribute to surface growth without increasing the number of cell layers

  28. L3 cells, or corpus layers, divide in both planes to add additional cell layers to the shoot.

  29. Organization of the SAM Fletcher 2003

  30. Shoot Apical Meristem The shoot apical meristem can be divided into distinct zones.

  31. -stem cells Shoot Apical Meristem The central zone is maintained as a pool of undifferentiated stem cells.

  32. -peripheral zone Shoot Apical Meristem The peripheral zone is the site of organ initiation.

  33. -stem cells -peripheral zone Shoot Apical Meristem As cell divisions occur in the central zone, the resulting cells are pushed into the peripheral zone where they are incorporated into organ primordia.

  34. Dividing Stem Cells are Pushed into the Peripheral Zone

  35. -stem cells -peripheral zone Shoot Apical Meristem The central zone cells will give rise to all of the above-ground organs of the mature plant.

  36. -stem cells -peripheral zone Shoot Apical Meristem How is the stem cell population maintained throughout the life of the plant?

  37. -stem cells -peripheral zone Shoot Apical Meristem A feedback loop between organ initiation and the stem cell population regulates the size of the meristem.

  38. Genes Controlling Meristem Development Normal heart- stage embryo WUS or STM mutant embryo WUSCHEL and SHOOTMERISTEMLESS mutants fail to develop a shoot apical meristem.

  39. STM and WUS mutants do not form a shoot apical meristem

  40. Genes Controlling Meristem Development Normal heart- stage embryo WUS or STM mutant embryo CLV1 or CLV3 mutant embryo CLAVATA1 and CLAVATA3 mutants develop a greatly enlarged shoot apical meristem.

  41. CLV1 mutants have a larger meristem and make more stem cells wt clv1

  42. clv3 mutants make more stem cells and resemble clv1 mutants Fletcher et al., 1999

  43. Genes Controlling Meristem Development • STM and WUS are required to form and maintain the stem cell population

  44. Genes Controlling Meristem Development • STM and WUS are required to form and maintain the stem cell population • CLV1 and CLV3 are required to prevent the over-proliferation of the undifferentiated stem cell population

  45. Genes Controlling Meristem Development • STM and WUS are homeobox genes and encode proteins that function as transcription factors

  46. Genes Controlling Meristem Development • STM and WUS are homeobox genes and encode proteins that function as transcription factors • CLV1 encodes a receptor protein

  47. Genes Controlling Meristem Development • STM and WUS are homeobox genes and encode proteins that function as transcription factors • CLV1 encodes a receptor protein • CLV3 encodes a small protein that functions as a signaling molecule that binds to the CLV1 receptor

  48. CLV / WUS Interactions CLV3 is expressed in the L1 and L2 cell layers of the central zone

  49. CLV / WUS Interactions CLV1 and WUS are expressed in a small domain of L3 cells in the central zone

  50. CLV / WUS Interactions CLV3 expression is lost in WUS mutants. Therefore, WUS activates CLV3 expression.

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