Download Ch 35 Control systems in plants

Bio 215: Chapter 39 Control systems in plants
Ch 39 Control systems in plants
Lecture
Control system in plants are adaptations that evolved over time in response to interactions with their environment. Plants
respond to environmental stiumui by
 sending signals between different parts of the plant.
 tracking the time of day and the time of year
 sensing and responding to gravity and directions of light
 adjusting their growth pattern and development.
1. Research on how plants grow toward light led to the discovery of plant hormones.
A. Hormone = a compound produced by one part of an organism that is transported to other parts where it triggers a
response in target cells and tissues
B. Phototropism is the growth of something to or away from light. Cells on the opposite side of the shoot elongate faster
than thoes on the light side.
C. Charles and Francis Darwin were some of the first researchers of phototropism
D. The plant hormone auxin was isolated by Kenneth Thimann
2.
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Plant hormones help coordinate growth, development and responses to environmental stimuli
 work by affecting division, eleongation and differentiation of cells.
A. Auxin: produced in apical meristem promotes elongation of young developing shoots
B. Cytokinins – stimulate cytokinesis, reduce aging, important in apical dominance and cell division
C. Gibberellins – produced in roots and young leaves, stimulate growth of leaves and stems, is involved in fruit
development and are used as a signal in a seed to break dormancy and apical bud dormancy and are antagonistic to
Abscisic acid
D. Abscisic Acid – produced in terminal bud and helps prepare plants for winter by suspending primary and secondary
growth are also involved in seed dormancy
E. Ethylene – gaseous hormone that diffuses in air and is responsible form fruit ripening and senescence of the plant,
also falling of leaves ( leaf absission)
Analysis of mutant plants is extending the list of hormones and their funtions.
 Until recently, plant hormne research was conducted mainly by applying ocmpounds to whole plants or tissue
cultures and measuring their effects on growth and development.
 Recently researches have used mutants to learn about the synthesis and action of hormones.
 recently identified hormones include oligosaccharides and brassinosteroids.
Signal transduction pathwyas ling cellular responses to hormonal signals and environmental stimuli.
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3.
Plant cell responses to hormone and environmental stimuli are mediated by intracellular signals (signal transduciton
pathways)
 Signal-transduciotn pathways are mechanisms linking a mechanical or chemical stimulus to the cellular
response.
 Three steps are involved reception, transduciton and induction.
A) Reception is the detection of a hormone or environmental stimulus by the cell.
 form depends on the stimulus like absorption of a particular wavelength., binding of a hormone
 reception of hormone only occurs in the targe cell that has a specific receptor for the hormone.
B) Transuciton is where we have amplifiaiocn of the stimulus and its conversion into a chemical form that can
activate the cells responses.
 the hormone bwill bind to a specific receptor that induces another sedond messenger.
 binding of hormone will result in a chemical change to the cell.
 a single hormone may give rise to many secondary messengers.
 two cell types may have receptors that bind to a hormone but the hormone may cause different secondary
messenters to form.
 some responses occur rapidly, some responses take a lot of time.
Tropism’s orient the growth of plant organs toward or away form stimuli.
A. Phototropism is a response to light that occurs in the shoot tip
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Bio 215: Chapter 39 Control systems in plants
4.
B. Gravitropism is an orientation of a plant in response to gravity
1) roots grow down - statoliths cause calcium and auxin to accumulate on lower side
2) shoots grow up –
C. Thigmotropism – is dirctional growth in response to touch (growth of tendrils around a branch)
Turgor movements are relatively rapid, reversible plant responses.
A. rapid leaf movements – rapid loss of turgor may cause special organs to move
B. Sleep Movements. – daily loss of turgor pressure at night lower the leaves in legumes
5.
Biological clocks control circadian rhythms in plants and other eukaryotes. Actual mechanism is unknown
A. all eukaryotes have a 24 hour clock that is reajusted daily by environmental cues
B. research is still under progress for this system
6.
Photoperiodism synchronizes many plant responses to changes of season.
A. Photoperiodic control of Flowering. (usually the length of night controls this)
1) short day plant require a light period shorter than a critical length and generally flower in late summer fall and winter
2) long day plants flower only when the light period is longer than a certain number of hours generally flower in late
spring and summer
3) day neutral plants are unaffected by photoperiod and flower when they reach a certain stage of maturity
7.
Phytochrome functions as a photoreceptor in many plant responses to light and photoperiod.
A. Ecological significance of Phytochrome as a Photoreceptor
1) very little phytochrome is in a plant and this signal is amplified in some way
2)
B. Interaction of Phytochrome and biological clock in Photoperiodism.
1) phytochrome is converted to a different form when exposed to light
2) at night this form reverts back to the inactive form
C. Red light (wavelength 660nm) is the most effective in interrupting night length.
1) brief exposure to short day plants to red light prevents flowering even if the plant is kept at critical night length
conditions.
2) long day plant is induced to flower by a brief exposure to red light even if kept at night lenghth eceeding the
critical number ofhours.
3) if a flash of red light if followed by a flash of far=red ight (wavelength 730nm) the plant perceives no
interruption of night length.
4) only the wavelength of the last flash affects the plat's measurement of night length, regarless of the number of
alternating flashes. see fig 39.18
8.
Control systems enable plants to cope with environmental stress
A. Responses to Water Deficit: guard cells, wilting, reduce growth
B. Responses to Oxygen Deprivation : may produce specialized structures to siphon air
C. Responses to Salt Stress: can be toxic, plant may produce a compatible solute so water is not lost due to osmosis
D. Responses to Heat Stress: transpiration, production of heat shock proteins
E. Responses to cold Stress: causes a change in the fluidity of cell membranes, will alter lipid content of membrane, Ice
crystals will rupture a cell.
F. Responses to Herbivores: plants begin to produce toxins or spines
G. Defense Against Pathogens: Systemic Acquired Resistance. Phytoalexin an antibiotic, salicylic acid is a signaling
hormone.
Things to know:
1) List the five classes of plant hormones and describe their function.
2) How does auxin initiate cell elongation.
3) Why is 2,4-D a widely used weed killer.
4) How does gibberillins trigger seed germination?
5) How doe plants tell up from down? What is the difference between positive and negative geotropism?
6) How does rapid leaf movement occur?
7) Describe the components of a signal – transduction pathway?
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Bio 215: Chapter 39 Control systems in plants
1) A hormone can
a) typically act on one type of cell that has a receptor for that hormone
b) will act on all tissues of a plant
c) usualy acts in conjunction or antagonistically with another hormone to control plant functions
d) can be gaseous and effect multiple plants
2) The local grocer has a load of green tomatoes, what could he do to make the tomatoes ripen faster.
a) expose the tomatoes to auxin
b) expose the tomatoes to cytokinins
c) expose the tomatoes to ethylene
d) expose the tomatoes to a mixture of auxin and cytokinin
e) expose the tomatoes to a mixture of 2 parts absciscic acid one part Gibberellin
3) Gravitoropism is the
a) movement of a plant away form light
b) the effect of a short pulse of night on flowering
c) movement of a plant towards touch
d) downward growth of the roots due to statoliths
4) In daylength effects on plants
a) short day plants require a light period shorter than a critical length
b) short day plants flower if night is longer then a critical length
c) long day plants flower only when the light period is longer than a critical length
d) long day plants need a night shorter than a critical length
e) The switch between critical day and night periods was discovered because when daytime period was broken by a
brief exposure to darkness their is no effect on flowering, however if nighttime is interrupted by short exposure to
light the plants do not flower.
5) When a plant is exposed to this stress it produces a different type of lipid that increases fluidity
a) pathogens
b) heat
c) water
d) cold
e) herbivores
Answers 1)a,c,d 2) c 3) d 4) b,d,e 5)d
Lecture
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What is a hormone?
Describe the functions of the following in coordinating plant growth and development:
a. Auxin
b. Cytokinins
c. Gibberellins
d. Abscisic acid
e. Ethylene
Describe how photoperiodism works and synchronizes plant responses to changes in season.
Why does 2,4-D widely used as a week killer.
How does light cause a phototropic response?
Distinguish among short-day plants, long -day plants, day neutral plants; give common examples of each.
Using photoperiodism as an example, explain how an integrated control system can regulate a plant process such as
flowering?
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