Dev. Bio

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Dev. Bio
2012-11-19 01:38:54
Section 13

Plants 3
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  1. Formation of root hairs
    Epidermis forms root hairs, trichomes (hair cells on stems and leaves), and stomata
  2. Function of root hairs
    • absorb water
    • allow bacteria to enter
    • grows in zone of differentiation from epidermal cells
  3. Hair cell precursors
    • form trichoblasts (hair precursors)
    • structurally different than atrichoblasts (non-hair epidermal cells)
    • Cortical cells provide signal--hair cells are next to 2 cortex cells whereas non-hair cells are next to only 1
  4. Glabra 2 (gl2) mutant
    all epidermal cells make root hairs

    normlly atrichoblasts produce gl2 which produce atrichoblasts

    if plant has gl2=no root hairs
  5. Trichomes-hair or leaves and stems
    • gl2 mutants-very hairy roots/no (or small) hair on leaves
    • transparent testa glubra (ttg)-same as gl2 mutants
    • Because: ttg stimulates ttg, then no gl2
    • Werewolf (wer) expressed in non hair cells (root) are required for differentiation-wer mutation=hairy roots
    • Glabral 1 (gl1)-expressed in epidermal cells of leaf and required for trichome formation
    • In root, wer, and leaf-gl1 is needed to stimulate gl2
  6. Stomata formation
    • Asymmetrical division yields guard mother cell (GMC)
    • Adjacent cells undergo asymmetric division-smaller ones close to GMC called subsidiary cells
    • GMC divides symmetrically producing guard cells
  7. Guard cells
    • Open during day/close at night
    • contain chlorophyll which causes swelling when uptaking H2O
  8. 6 Plant hormones
    • Abscisic acid
    • Auxin
    • Brassinosterioids
    • Cytokinins
    • Ethylene
    • Giberillins
  9. Abscisic acid (ABA)
    • stomata closure
    • maintenance of dormancy
    • prevents germination
  10. Auxin
    • apical dominance
    • cell elongation
    • phototropism
    • geotropism
    • fruit development
    • xylem regeneration in wound healing
    • adventitous root formation
  11. Brassinosteroids
    • cell elongation
    • cell division
    • produces steroid reductase enzyme (in humans would produce testosterone)
    • mutant would get short plant
    • overexpress would get large plant
  12. Cytokinins
    • cell division yielding shoot formation in culture
    • delay of leaf senescence
    • release of apical buds
  13. Ethylene (gas)
    • induced by auxin
    • causes fruit ripening
    • root hair growth
    • abscission
    • senescence-when plant becomes dormant in winter
  14. Gibberillins
    • cell elongation
    • floral induction
    • seed germination
  15. Atpin mutants-auxin transport
    • auxin is the oldest studied plant hormone
    • auxin weakens the cell which allows for elongation

    • aux1-transport auxin to cells
    • atpin1-transport of auxin
  16. More on auxin
    • can flow down stem or up stem
    • sunlight inhibits auxin-this explains why stem grows towards sun (cells opposite sun can elongate w/ auxin present
    • auxin in influenced by gravity--if laid on side, shoots would grow up and roots would grow down 
  17. Plants response to hormones
    • cytokinin stimulate cell division-antagonist to auxin-excess of cytokinin (from supershoot (sps)) causes very bushy plant
    • Gibberillin pormotes tall and skinny growth-"foolish seedling disease"
  18. Hormone mutants
    • Gn1 mutants-no gibberillin-short plants
    • Gai mutants-insensitive to gibberillin-short plant
    • spindly-acts like too much gibberillin-tall plant
  19. Phytoreceptors
    Red light-daylight, bottom of lake--causes phytochromes to enter nucleus, bind with a protein that binds DNA

    Far red light-moonlight,shade under tree--causes phytochromes to leave nucleus