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Formation of root hairs
Epidermis forms root hairs, trichomes (hair cells on stems and leaves), and stomata
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Function of root hairs
- absorb water
- allow bacteria to enter
- grows in zone of differentiation from epidermal cells
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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
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Glabra 2 (gl2) mutant
all epidermal cells make root hairs
normlly atrichoblasts produce gl2 which produce atrichoblasts
if plant has gl2=no root hairs
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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 gl2...no 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
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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
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Guard cells
- Open during day/close at night
- contain chlorophyll which causes swelling when uptaking H2O
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6 Plant hormones
- Abscisic acid
- Auxin
- Brassinosterioids
- Cytokinins
- Ethylene
- Giberillins
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Abscisic acid (ABA)
- stomata closure
- maintenance of dormancy
- prevents germination
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Auxin
- apical dominance
- cell elongation
- phototropism
- geotropism
- fruit development
- xylem regeneration in wound healing
- adventitous root formation
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Brassinosteroids
- cell elongation
- cell division
- produces steroid reductase enzyme (in humans would produce testosterone)
- mutant would get short plant
- overexpress would get large plant
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Cytokinins
- cell division yielding shoot formation in culture
- delay of leaf senescence
- release of apical buds
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Ethylene (gas)
- induced by auxin
- causes fruit ripening
- root hair growth
- abscission
- senescence-when plant becomes dormant in winter
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Gibberillins
- cell elongation
- floral induction
- seed germination
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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
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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
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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"
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Hormone mutants
- Gn1 mutants-no gibberillin-short plants
- Gai mutants-insensitive to gibberillin-short plant
- spindly-acts like too much gibberillin-tall plant
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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
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