Agenda

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• 
  Agenda
• Practical
• Lecture Leaf Anatomy, Plant Hormones
• Lab Leaf Anatomy, Plant Hormones
• Next week lab reports are due, turn in your
  clean pots

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Leaf Anatomy
Blade
Axillary Bud
Node
Petiole
Sheath
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Petiole of aspen is flattened
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Some leaves have no petiole
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Alternate
Whorled
Opposite
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Compound leaf is a leaf whose blades are divided
into several distinct leaflets
Simple leaf is an undivided leaf
Each leaf, whether simple or compound, has a bud
at its base (on the twig). There are no buds at
the base of each leaflet.
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Pinnately compound leaflets arranged linearly
along both sides of the axis
Palmately compound leaflets all attached at one
point near the tip of the petiole
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Upper epidermis
Palisade Mesophyll
Spongy Mesophyll
Guard cells, surrounding the stomata
Lower epidermis
Vascular bundle
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Stomata opening for entry of gasses in and out
of the leaf. What are some important
gases? Guard cells changes in turgor pressure
cause opening and closing of the stomata
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Hormone
Compound produced in one part of the body and
then transported to another part, elicits a
response, only small quantities needed
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What does it Do?Generalpromotes cell
elongation. Specific Auxin maintains apical
dominance, blocks leaf abscission, can induce
fruit development without pollination. The
natural auxin occurring in plants is indoleactic
acid. Apical meristem is a major site of auxin
synthesis. Experiment 1 cut the tip off of
plants and applied IAA to some tips and not
others. Experiment 2 cut off the leaf blade
but left the petiole. Applied IAA to some
petiole tips and not others
Auxin
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What does it Do? is a gas produced by ripe
fruits. Also produced as a wound or stress
response. Can cause epinasty. sometimes
applied to plants to get them all to ripen at the
same time reason why one bad apple spoils the
bunch can cause epinasty (twisted appearance
due to differential growth)Experiment Put a
tomato plant in a box with fruit of a ripening
apple.Put a tomato plant in a box without fruit
of a ripening apple.What will the apple
produce? What affect will the chemical have on
the tomato plant?
Ethylene
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What does it Do? promote cell division, delays
senescence. used commercially in floral
displaysExperiment Barley leaves were placed
in test tubes (some with zeatin and some without
zeatin).Zeatin is a naturally occuring
cytokinin. What visual difference do you expect
to see between the two treatments?
Cytokinins
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What does it Do?Slows down growth, promotes seed
dormancy. It is also involved in opening and
closing of stomata as leaves wilt. Experiment
We planted some seeds with Abscisic acid and
some without.Which will germinate and which will
not?
Abscisic Acid
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What does it Do?promotes stem elongation, over
100 naturally occurring gibberellins, can break
seed dormancy can be sprayed on fruits to make
them bigger (ex. Thompsons grapes)Experiment
Applied gibberellin to both dwarf pea plants and
regular pea plants.What will happen?
Gibberellins
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2,4 D

• Synthetic auxin
• Works as an herbicide
• Only works on dicots

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Phytochrome

• Receptor molecules that can change shape in
  response to the type of light the plant is
  exposed to Pr or Pfr . The Pr shape senses red
  light. The Pfr shape senses far red light.
• A shift from Pr to Pfr shape initiates some plant
  responses. Important plant responses regulated
  by the phytochrome system include seed
  germination, photoperiodic induction of
  flowering, chloroplast development (not including
  chlorophyll synthesis), leaf senescence and leaf
  abscission.
• See pg. 818 in Campell

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Tropism

• Movement toward or away from a stimulus-
  phototropism
• - gravitropism
• - thigmotropism