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Growth and Development & Plant Hormones Part 1 Flashcards

1
Q

Growth results from:

A

– cell division
– cell enlargement

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2
Q

Development

A

coordination of growth and differentiation into
tissues, organs, and the whole organism

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3
Q

Plant hormone

A

Naturally occurring organic substance produced in minute
quantities in one part of the plant and then transported to
another part of the plant where it controls or affects growth and
development

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4
Q

Plant hormone

A

Present in nanogram/gram fresh weight
– (1 nanogram = 1.0×10-9 grams)

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5
Q

Plant growth regulators:

A

– Both natural and synthetic substances that affect plant
development as hormones do
– Includes plant hormones
– Also active at low concentrations

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6
Q

Major Groups of Known Plant Hormones

A
  • Auxins
  • Gibberellins
  • Cytokinins
  • Ethylene
  • Abscisic Acid
  • (Brassinosteroids)
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7
Q

Auxein (Greek) =

A

to increase

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8
Q

IAA (indole acetic acid)

A
  • promotes cell enlargement
  • sometimes promotes cell division
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9
Q

Charles Darwin and his son Francis provided

A

early evidence for
the existence of auxin

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10
Q

auxins have positive effects but at high concentration it can also

A

Auxins have growth promoting and other positive effects BUT at
high concentration auxins can inhibit growth

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11
Q

whats more sensitive to auxin roots or shoots

A

Roots more sensitive to auxin than shoots

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12
Q

adding auxin to roots can

A

inhibit growth

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13
Q

What is more sensitive to auxin

dicots or monocots

A

Dicots mores sensitive to auxin than monocots

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14
Q

Some herbicides contain

A

2,4D (synthetic auxin)
that kills dicot weeds

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15
Q

Auxin is synthesized in

A

meristematic regions

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16
Q

where specifically is auxin synthesized in meristematic regions

A

-shoot tips
-root tips
-germinating seeds

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17
Q

Auxin also synthesized in

A

– young, rapidly growing leaves
– developing flowers
– young embryos following fertilization.

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18
Q

Polar Transport of IAA

where

A

In the shoot, Polar Transport of IAA in
parenchyma cells in contact with vascular
bundles.

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19
Q

Polar Auxin Transport

As it is transported downwards, it causes:

A

– Root initiation of cuttings
– Vascular tissue differentiation
– Inhibition of axillary bud growth

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20
Q

Roles of Auxin: 1

A

1) Causes Root Initiation

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21
Q

1) Causes Root Initiation

A

-Occurs naturally when a
cutting is placed in
water

-Auxin can be added to
the base of cuttings to
enhance the process of
root initiation

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22
Q

Auxin is the active ingredient in rooting powders.

A

rooting powders

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23
Q

too much rooting powder can

A

inhibit
root growth.

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24
Q

role 2 of auxin

A

Auxin Causes Vascular
Tissue Differentiation

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25
Auxin Causes Vascular Tissue Differentiation
When the xylem of a plant stem is cut, new xylem forms around the wound.
26
evidence for a role of auxin in xylem differentiation
-In this demonstration, the top of the plant was cut off to remove the tip of the plant, the natural source of auxin. * The plant was wounded and the vascular tissue was cut * IAA was added in a paste above the wound, and the xylem regenerated around the wound without the tip of the plant
27
Roles of Auxin 3
Inhibits the growth of lateral buds, promoting apical dominance (tip of plant (apex) is dominant over lateral buds)
28
Auxin in an agar block will also substitute for
the tip
29
There is more auxin near the
tip of the plant
30
Growth of the axillary buds is more inhibited closer to the
tip
31
If the tip is removed, the axillary buds will grow because the
main source of auxin has been removed
32
If the tip of a plant is cut off the
axillary bud will grow
33
If the tip is cut off and replaced with auxin
(axillary) buds do not grow
34
apical dominance Strong in trees
with conical shapes (e.g. Pines, spruces, firs) Norfolk Island Pine
35
Apical Dominance
Weak in trees that branch more often (e.g. Elms, ashes, willows) Weeping Willow
36
roles of Auxin 4
4) Involvement in tropisms
37
tropism
directional response of a plant part to an external stimulus in which the direction of the response depends on the direction of the stimulus
38
Positive phototropism of shoots
More auxins accumulate on the side in the shade, so the cells grow faster on the shaded side, making the shoot grow towards the sun.
39
b. Negative gravitropism of shoots
Shoots grow away from the direction of gravity
40
c. Positive gravitropism of roots
Shoots grow toward the direction of gravity
41
Roles of Auxin Continued 5
5) Inhibits leaf and fruit abscission.
42
Leaf Abscission in the Autumn
-Young leaves in spring and summer produce auxin that travels through the petiole preventing abscission * Older leaves in autumn no longer produce enough auxin and the abscission zone forms.
43
Roles of Auxin Continued 6
6) Promotes flowering in pineapples
44
G) Roles of Auxin Continued 7
7) Stimulates fruit development
45
Parthenocarpy:
seedless fruits
46
Some species will produce seedless fruits after spraying the flowers with
auxin early in ovule development: – Tomatoes – Eggplants – Cucumbers
47
Apple Orchards auxin
* Spray with auxin: – to promote uniform flowering – to promote uniform fruiting – to prevent early abscission of fruits
48
Roles of Auxin: 8)
controls weeds
49
2,4-D and 2,4,5-T herbicides (synthetic auxins) in
Agent Orange (Defoliant in Vietnam War)
50
2,4,5-T banned for most uses in 1979 due to
dioxin contaminants * Leukemia * Miscarriages * Birth Defects * Lung & Liver Diseases
51
2,4-D is
still used * Moderate toxicity for mammals and birds
52
Roles of Auxin Continued 9
9) Promotes cell division in tissue culture
53
Gibberellins =
GA'sa over 135 diffrent kinds
54
Gibberellic acid effects
– Growth promoting and other positive effects – Promotes cell division and cell enlargement
55
Discovery of Gibberellins (GA’s)
1) In Japan in the 1930’s (unknown in Western part of World)
56
2) Foolish seedling disease (Bakane)
– Gibberella fujikuroi – Culture medium that fungus was in or fungal extract caused symptoms -Infected seedlings exhibit abnormal elongation and in severe cases stunting leading to death. It led to the discovery of GA.
57
Roles of GA’s 1
1) Promote stem elongation of intact plants
58
Cabbage rosettes
bolt and flower following treatment with gibberellins. *Bolting typically occurs due to low temperatures and longer days. *GA’s substitute for environmental cues.
59
Affects of Added GA’s on Stems
* Short bush beans become climbing pole beans * Genetically dwarf rice, maize, peas become phenotypically tall. * Genetically tall plants have little response to added GA’s
60
C) Roles of GA’s continued 2
Promote germination of dormant seeds and growth of buds.
61
C) Roles of GA’s continued 3
3) Can cause flowering.
62
C) Roles of GA’s continued 4
4) Promotes fruit development and formation
63
GA and promoting fruit gas use (grapes and its costs)
-Used to increase the size of Thompson seedless grapes and makes less tightly packed bunches. – Costly as Gibberella fujikuroi is still the source of GA3
64
Roles of cytokinins
1. Promote cell division (cytokinesis) 2. Produced in roots * Promotes shoot formation * Promotes growth of lateral buds 3. Cause cell division in tissue culture * also differentiation of shoots in tissue culture
65
Buds closer to tip of plant have more auxin and less
cytokinins from the roots, so buds are inhibited.
66
Buds at nodes closer to base of plant have more
cytokinins from the roots and less auxin from the tip, so buds are less inhibited and they start to grow. Buds closer to tip of plant have more auxin and less cytokinins from the roots, so buds are inhibited. Cytokinins from Roots also Affect Growth of Axillary Buds
67
High cytokinin to auxin ratio
promotes shoot differentiation promotes root differentiation
68

botany (25 decks)

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