1 Responses to Light Photomorphogenesis refers to non- directional, light-triggered development...
-
Upload
dwight-fowler -
Category
Documents
-
view
231 -
download
2
Transcript of 1 Responses to Light Photomorphogenesis refers to non- directional, light-triggered development...
![Page 1: 1 Responses to Light Photomorphogenesis refers to non- directional, light-triggered development Phototropisms are directional growth responses to light.](https://reader035.fdocuments.us/reader035/viewer/2022062217/5697bff01a28abf838cba782/html5/thumbnails/1.jpg)
1
Responses to LightPhotomorphogenesis refers to non-directional, light-triggered
development
Phototropisms are directional growth responses to light
Both compensate for plants’ inability to move
The phytochrome molecule exists in two interconvertible forms:
-Pr is the inactive form
-Absorbs red light at 660 nm
-Pfr is the active form
-Absorbs far-red light at 730 nm
![Page 2: 1 Responses to Light Photomorphogenesis refers to non- directional, light-triggered development Phototropisms are directional growth responses to light.](https://reader035.fdocuments.us/reader035/viewer/2022062217/5697bff01a28abf838cba782/html5/thumbnails/2.jpg)
2
Responses to Light1. Seed germination
-Inhibited by far-red light and stimulated by red light in many plants
2. Shoot elongation
-Etiolation occurs when shoot internodes elongate because red light and active Pfr are not available
3. Detection of plant spacing
-Crowded plants receive far-red light bounced from neighboring plants
-This increases plant height in competition for sunlight
![Page 3: 1 Responses to Light Photomorphogenesis refers to non- directional, light-triggered development Phototropisms are directional growth responses to light.](https://reader035.fdocuments.us/reader035/viewer/2022062217/5697bff01a28abf838cba782/html5/thumbnails/3.jpg)
3
Responses to LightPhytochromes are involved in many signaling
pathways that lead to gene expression
-Pr is found in the cytoplasm
-When it is converted to Pfr it enters the nucleus
-Pfr binds to transcription factors, leading to expression of light-regulated genes
![Page 4: 1 Responses to Light Photomorphogenesis refers to non- directional, light-triggered development Phototropisms are directional growth responses to light.](https://reader035.fdocuments.us/reader035/viewer/2022062217/5697bff01a28abf838cba782/html5/thumbnails/4.jpg)
4
PhototropismsPhototropic responses including the bending of
growing stems to sources of light with blue wavelengths (460-nm range)
![Page 5: 1 Responses to Light Photomorphogenesis refers to non- directional, light-triggered development Phototropisms are directional growth responses to light.](https://reader035.fdocuments.us/reader035/viewer/2022062217/5697bff01a28abf838cba782/html5/thumbnails/5.jpg)
5
Circadian Clocks
Circadian rhythms (“around the day”) are particularly common among eukaryotes
Have four characteristics:
1. Continue in absence of external inputs
2. Must be about 24 hours in duration
3. Cycle can be reset or entrained
4. Clock can compensate for differences in temperature
![Page 6: 1 Responses to Light Photomorphogenesis refers to non- directional, light-triggered development Phototropisms are directional growth responses to light.](https://reader035.fdocuments.us/reader035/viewer/2022062217/5697bff01a28abf838cba782/html5/thumbnails/6.jpg)
6
Responses to GravityGravitropism is the response of a plant to the
gravitational field of the Earth
Four general steps of a gravitropic response:
1. Gravity is perceived by the cell
2. A mechanical signal is transduced into a gravity-perceiving physiological signal
3. Physiological signal is transduced to other cells
4. Differential cell elongation occurs in the “up” and “down” sides of root and shoot
![Page 7: 1 Responses to Light Photomorphogenesis refers to non- directional, light-triggered development Phototropisms are directional growth responses to light.](https://reader035.fdocuments.us/reader035/viewer/2022062217/5697bff01a28abf838cba782/html5/thumbnails/7.jpg)
7
Responses to GravityShoots exhibit negative gravitotropismIn shoots, gravity is sensed in endodermal cells surrounding the vascular tissue
-Signaling is in the outer epidermal cells
Roots have a positive gravitropic response
In roots, the cap is the site of gravity perception
-Signaling triggers differential cell elongation and division in the elongation zone
![Page 8: 1 Responses to Light Photomorphogenesis refers to non- directional, light-triggered development Phototropisms are directional growth responses to light.](https://reader035.fdocuments.us/reader035/viewer/2022062217/5697bff01a28abf838cba782/html5/thumbnails/8.jpg)
8
Response to GravityAuxin accumulates on lower
side of the stem
-Results in asymmetrical cell elongation and curvature of the stem upward
Lower cells in root cap are less elongated than those on upper side
-Upper side cells grow more rapidly causing the root to ultimately grow downward
![Page 9: 1 Responses to Light Photomorphogenesis refers to non- directional, light-triggered development Phototropisms are directional growth responses to light.](https://reader035.fdocuments.us/reader035/viewer/2022062217/5697bff01a28abf838cba782/html5/thumbnails/9.jpg)
9
Responses to Mechanical StimuliThigmomorphogenesis permanent form
change in response to mechanical stresses
Thigmotropism directional growth of a plant in response to contact
Thigmonastic responses occur in same direction independent of the stimulus
Examples of touch responses:
-Snapping of Venus flytrap leaves curling of tendrils around objects
![Page 10: 1 Responses to Light Photomorphogenesis refers to non- directional, light-triggered development Phototropisms are directional growth responses to light.](https://reader035.fdocuments.us/reader035/viewer/2022062217/5697bff01a28abf838cba782/html5/thumbnails/10.jpg)
10
Responses to Mechanical StimuliSome touch-induced plant movements involve
reversible changes in turgor pressure
-Touch triggers movement of ions to outer side of pulvini
-Water follows by osmosis
-Decreased interior turgor pressure causes the leaf to fold
![Page 11: 1 Responses to Light Photomorphogenesis refers to non- directional, light-triggered development Phototropisms are directional growth responses to light.](https://reader035.fdocuments.us/reader035/viewer/2022062217/5697bff01a28abf838cba782/html5/thumbnails/11.jpg)
11
Responses to Mechanical StimuliSome turgor movements are triggered by light
-This movement maximizes photosynthesis
Bean leaves are horizontal during the day when their pulvini are rigid
-But become more or less vertical at night as the pulvini lose turgor
![Page 12: 1 Responses to Light Photomorphogenesis refers to non- directional, light-triggered development Phototropisms are directional growth responses to light.](https://reader035.fdocuments.us/reader035/viewer/2022062217/5697bff01a28abf838cba782/html5/thumbnails/12.jpg)
12
Water and Temperature ResponsesAbscission involves changes at the petiole’s base
Protective layer = Consists of several layers of suberin-impregnated cells
Separation layer = Consists of 1-2 layers of swollen, gelatinous cells
ind and rainseparate the leaf from the stem
-Nutrient sinks are discarded, conserving resources
![Page 13: 1 Responses to Light Photomorphogenesis refers to non- directional, light-triggered development Phototropisms are directional growth responses to light.](https://reader035.fdocuments.us/reader035/viewer/2022062217/5697bff01a28abf838cba782/html5/thumbnails/13.jpg)
13
Seed DormancyAccumulating food reserves, forming a protective seed
coat and dehydration
Offspring to wait until conditions for germination are optimal
-Legume seeds last decades or longer
-Seeds that are thousands of years old have been successfully germinated
![Page 14: 1 Responses to Light Photomorphogenesis refers to non- directional, light-triggered development Phototropisms are directional growth responses to light.](https://reader035.fdocuments.us/reader035/viewer/2022062217/5697bff01a28abf838cba782/html5/thumbnails/14.jpg)
14
AuxinDiscovered in 1881 by Charles and Francis
Darwin
![Page 15: 1 Responses to Light Photomorphogenesis refers to non- directional, light-triggered development Phototropisms are directional growth responses to light.](https://reader035.fdocuments.us/reader035/viewer/2022062217/5697bff01a28abf838cba782/html5/thumbnails/15.jpg)
15
Auxin In 1926, Frits Went performed an experiment that explained all of the previous results
-He named the chemical messenger auxin
-Cell elongation causes the plantto bend towards light
![Page 16: 1 Responses to Light Photomorphogenesis refers to non- directional, light-triggered development Phototropisms are directional growth responses to light.](https://reader035.fdocuments.us/reader035/viewer/2022062217/5697bff01a28abf838cba782/html5/thumbnails/16.jpg)
16
AuxinWinslow Briggs later demonstrated that auxin molecules migrate away from the light into the shaded portion of the shoot
-Barriers in a shoot tip revealed equal amounts of auxin in both the light and dark sides
-However, different auxin concentrations produced different degrees of curvature
![Page 17: 1 Responses to Light Photomorphogenesis refers to non- directional, light-triggered development Phototropisms are directional growth responses to light.](https://reader035.fdocuments.us/reader035/viewer/2022062217/5697bff01a28abf838cba782/html5/thumbnails/17.jpg)
17
How Auxin WorksIndoleacetic acid (IAA) is the most common natural
auxin
-Probably synthesized from tryptophan
![Page 18: 1 Responses to Light Photomorphogenesis refers to non- directional, light-triggered development Phototropisms are directional growth responses to light.](https://reader035.fdocuments.us/reader035/viewer/2022062217/5697bff01a28abf838cba782/html5/thumbnails/18.jpg)
18
Synthetic Auxins
Naphthalene acetic acid (NAA) and indolebutyric acid (IBA) have many uses in agriculture and horticulture
-Prevent abscission in apples and berries
-Promote flowering & fruiting in pineapples
2,4-dichlorophenoxyacetic acid (2,4-D) is a herbicide commonly used to kill weeds
![Page 19: 1 Responses to Light Photomorphogenesis refers to non- directional, light-triggered development Phototropisms are directional growth responses to light.](https://reader035.fdocuments.us/reader035/viewer/2022062217/5697bff01a28abf838cba782/html5/thumbnails/19.jpg)
19
Cytokinins Are purines that appear to be derivatives of adenine
Synthetic cytokinins
Cytokinins are produced in the root apical meristems and fruits
-Stimulate cell division and differentiation & promote the growth of lateral buds into branches
![Page 20: 1 Responses to Light Photomorphogenesis refers to non- directional, light-triggered development Phototropisms are directional growth responses to light.](https://reader035.fdocuments.us/reader035/viewer/2022062217/5697bff01a28abf838cba782/html5/thumbnails/20.jpg)
20
GibberellinsNamed after the fungus Gibberella fujikuroi which
causes rice plants to grow very tall
Gibberellins belong to a large class of over 100 naturally occurring plant hormones
-All are acidic
-Have important effects on stem elongation
![Page 21: 1 Responses to Light Photomorphogenesis refers to non- directional, light-triggered development Phototropisms are directional growth responses to light.](https://reader035.fdocuments.us/reader035/viewer/2022062217/5697bff01a28abf838cba782/html5/thumbnails/21.jpg)
21
BrassinosteroidsFirst discovered in the pollen of Brassica spp.
-Are structurally similar to steroid hormones-Elongation, cell division, stem bending, vascular tissue development, delayed senescence and reproductive development
![Page 22: 1 Responses to Light Photomorphogenesis refers to non- directional, light-triggered development Phototropisms are directional growth responses to light.](https://reader035.fdocuments.us/reader035/viewer/2022062217/5697bff01a28abf838cba782/html5/thumbnails/22.jpg)
22
Oligosaccharins
Are complex plant cell wall carbohydrates that have a hormone-like function
-Can be released from the cell wall by enzymes secreted by pathogens
-Signal the hypersensitive response (HR)
In peas, oligosaccharins inhibit auxin-stimulated elongation of stems
-While in regenerated tobacco tissue, they inhibit roots and stimulate flowers
![Page 23: 1 Responses to Light Photomorphogenesis refers to non- directional, light-triggered development Phototropisms are directional growth responses to light.](https://reader035.fdocuments.us/reader035/viewer/2022062217/5697bff01a28abf838cba782/html5/thumbnails/23.jpg)
23
EthyleneA gaseous hydrocarbon (H2C–CH2)
-thus retards their growth in lateral bud
-suppresses stem and root elongation
Ethylene controls leaf, flower and fruit abscission
It hastens fruit ripening
-Indeed, an antisense copy of the gene has been used to create transgenic tomato
-These stay fresh longer
![Page 24: 1 Responses to Light Photomorphogenesis refers to non- directional, light-triggered development Phototropisms are directional growth responses to light.](https://reader035.fdocuments.us/reader035/viewer/2022062217/5697bff01a28abf838cba782/html5/thumbnails/24.jpg)
24
Abscisic AcidAbscisic acid is synthesized mainly in mature
green leaves, fruits and root caps
-induces formation of dormant winter buds
-necessary for dormancy in seeds
-important in the opening and closing of stomata
-Triggers movement of K+ out of guard cells