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39 Cards in this Set

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what is a natural type of auxin
There is only one naturally occurring auxin: indole-3-acetic acid (IAA) and this is chemically related to the amino acid tryptophan.IAA, IBA, 4-Cl-IAA, IAA
Auxin synthetic type
naphthalene acetic acid (NAA) is used to control fruit set and sucker growth on trees after pruning.

Indole butyric acid is used to promote rooting in cuttings.

Far and away the biggest use of auxin-like compounds is as herbicides (2,4-D and MCPA).

Applied at high concentration they promote uncoordinated growth and finally death, particularly in broad-leaved weeds.agent orange
natural and synthetic type of cytokinin
Zeatin
Kinetin
describe auxin
Plant growth substance (phytohormones, hormones). "acid growth theory" auxins stimulated cell elongation in young stems, cuasing responsive cells to actively transport H+ ions out of cell, lowering pH around cells. This acidification of cell wall region activates expansin enzymes which break cell wall bonds---> lessen rigidity, allowing elongation. Causes phototropism - bending to light. High concentrations stimulates ethylene prod which stops growth and may cause leaves to senesce fall off and kill plant.
describe GA
stem elongation,
mobilization of food reserves in seeds & ect processes.
dwarfism of some plants.

terpenoid pathway in plastids and modified in ER & cytosol before reaching activated form.

Orig derived from gibberella fungus
describe ABA
Triggers abscission, stimulates ethylene production, inhibits growth and stomatal opening under envir.stress. Secondary metabolite in fungi.
describe cytokinin
cell division. cell growth & differentiation ect.
describe phytochromes
Seeds germinated in the dark produce pale, spindly seedlings. – etiolated
Expose a dim light to seedlings and chloroplasts will form. – photomorphogenesis
Absorption/action spectrum indicates that red and far-red light is responsible.
Pigment responsible is phytochrome, a protein blue pigment common in etiolated parts of a plant.
Lewis Flint demonstrated that the effects of red light (650 to 680) is reversed by far-red light 710-740) in lettuce seed germination.
17.2

Several activities are controlled by photoreversible response.
17.1

Pr/Pfr model
17.3

Structure of Pr and Pfr
Pfr is the physiologically active form
Phytochrome synthesis involves phytochromobilin formed in plastids and a phytochrome apoprotein synthesized in the cytoplasm.
17.6

Distribution of phytochrome
Phytochrome responses can be distinguished by the amount of light required
VLFRs – very low fluence responses are nonphotoreversible
LFRs – low fluence responses are photoreversible
HIRs – high fluence responses are propotional to irradiance

Table 17.2 and 17.3
Photoperiodism ability of an organism to detect day length
Short Day Plants example – Chrysanthem morifolium, Xanthium strumarium
Long Day Plants example – Spinach
Plants Monitor Day Length by measuring the length of the Night
Leaf is the Site of Perception of the Photoperiodic Stimulus
Phytochrome is the main Photoreceptor
Phytochrome regulates certain daily rhythms, circadian rhythms (nyctinasty in leaves – pulvinus of legumes)
describe ethylene
Ethylene is the only gaseous hormone in the plant world; it is a simple hydrocarbon gas that is derived from the amino acid, methionine, via an unusual cyclic compound which is also an amino acid, ACC (1-aminocyclopropane-1-carboxylic acid).The gas is used commercially for ripening fruit, particularly bananas.
auxin is produced
in the stem tip
GA produced
in stem rather than growing tip
ABA produced
biosynthesis primarily occurs in the leaves
auxin degredation
Of IAA via oxidative degrdtn. Controls development of IAA / does not degrade synthetic auxins. Degradation of auxin is the final method of controlling auxin levels.
cytokinin degredation
irreversible degredation via cytokinin oxidases; regulation role in hormone levels
Describe wents curvature test
1 etiolated coleoptile;
2 decapitation: the extreme tip of the coleoptile is removed (1mm),
3 second decapitaion (2-4 mm),
4 removal of the primary leaf,
5 removal of tip;
6 Auxin-containing gelatine block is placed on one side of the amputed tip of the seedling,
7 tip always bent away from the side on which the gelatine block was placed.

Model studies with isolated membrane vesicles (like isolated vacuoles) have been carried through in order to understand the influence of auxins on membranes

Experiments with plasma membrane vesicles showed that the accumulation of auxin is dependent on pH and electron potential.
auxin transport
1. Polar transport in parenchyma cells assoc w/vascular tissue. 2 types: #1 IAA influx - pH depenent, passive transport of undissociated form, or active H+ cotransport mechanism driven by plasma membrane. #2 IAA efflux - at basal ends of transprtg cells via anion efflux carriers driven by emmbrane potl generated by membrane H+-ATPase. ATI's - competitive inhibitors can interrupt transport
cytokinin transport
Passive non polar transport from root to shoot via xylem (w/ minerals & H2O). In Pea plants: shoot can regulate flow of cytokinin from root.
ga transport
non-polar, bidirectional producting general responses
aba transport
transport of ABA can occur in both xylem and phloem tissues. It can also be translocated through paranchyma cells. The movement of abscisic acid in plants does not exhibit polarity like auxins. ABA is capable of moving both up and down the stem
ehtylene transport
Gas generally diffuses rapidly but not under waterlogging immersion.
auxin funx
"Indole Acetic Acid (IA). that promotes cell elongation. Auxin moves to the darker side of the plant, causing the cells there to grow larger than corresponding cells on the lighter side of the plant. This produces a curving of the plant stem tip toward the light, a plant movement known as phototropism. Auxin also plays a role in maintaining apical dominance. Most plants have lateral (sometimes called axillary) buds located at nodes (where leaves attach to the stem). Buds are embryonic meristems maintained in a dormant state. Auxin maintains this dormancy. As long as sufficient auxin is produced by the apical meristem, the lateral buds remain dormant. If the apex of the shoot is removed (by a browsing animal or a scientist), the auxin is no longer produced. This will cause the lateral buds to break their dormancy and begin to grow. In effect, the plant becomes bushier. When a gardener trims a hedge, they are applying apical dominance.

"
Plant growth substance (phytohormones, hormones). "acid growth theory" auxins stimulated cell elongation in young stems, cuasing responsive cells to actively transport H+ ions out of cell, lowering pH around cells. This acidification of cell wall region activates expansin enzymes which break cell wall bonds---> lessen rigidity, allowing elongation. Causes phototropism - bending to light. High concentrations stimulates ethylene prod which stops growth and may cause leaves to senesce fall off and kill plant.
cyto funx
Class of plant growth substance (plant homones). Promotes cell division. Involved in cell growth & differentiation ect. Exp: kinetin, zeatin, benzyl adenein; discovered effects in coconut milk
ga funx
1. Produces Seed germination - Barley de novo amylase sunthesis. 2. Stimulates shoot & cell elongation 3. Reverses dwarfism 4. Stimulates bolting & Flowering in biennials. 5. Control of sex expression. 6. Fruit growth (seedless grapes). 7. Delays leaf senescence 8. Inhibits adventitiuous root growth (reg & adventitious) 9. promotes root initiation in low conc in pea cuttings. 10. regulates production of hyro enzymes for starch digestion 11. Breaks dormancy 12. indeces extra chlorophyll production 13. stimulates root senescence
A plant growth substance (phytohormone) involved in protion of stem elongation, mobilization of food reserves in seeds & ect processes. Its absence results in dwarfism of some plants. Family of diterpene acids made by terpenoid pathway in plastids and modified in ER & cytosol before reaching activated form. Orig derived from gibberella fungus
aba funx
"ABA closes stomata during water stress


1. Prevents stomatal opening by inhibiting inward
K ion channels and plasma membrane proton pumps

2. Promotes stomatal closing by activating outward
anion channels, thus leading to activation of potassium ionse
efflux channels.

"
Triggers abscission, stimulates ethylene production, inhibits growth and stomatal opening under envir.stress. Secondary metabolite in fungi.
ethylene funx
1. Fruit ripenin 2.stem elongation 3. Abscission leaf flower & fruits (thinning, harvestin) 3. Epinasty (bending of leaves downward) 4. Triple responses 5. Induces flowering in pineapples. 6. Hook closure maintenance 7.can initiate germination in cereal grains once dormancy is broken by it 8. Activates dormant buds (potatoes in storage) 9. 10. female expression in flowers 11.can break dormancy (in cereals) & bud dormancy 13.flower & leaf senescence
auxin stimulates
"1. Cell division with CK 2. elongation, via H+ export
3.ethylene production
RNA synthesis. MODE OF ACTION: 1° - early stimulation (10-15 min.)
2° - triggers intracellular receptor"
cyto stimulates
cell division
GA stimulates
"1.seed germination (stratification)
2. cell elongation
3. flower bud formation (vernalization)
4. proteases, RNAses
5. alpha-amylase transcription 6. Bolting and flowering in biennials 7. root senescence"
ABA stimulates
"1. abscission
2. bud dormancy
3. stomatal closure
4. transcription of storage protein mRNAs"
ethylene stimulates
"1. disease/wounding resistance
2. abscission"
Why doesn't IAA elongate cells in stem?
Cells may not have genes there for developing elongation.
What are statoliths?
Starch filled amyloplasts, in statocytes are involved in normal perception of gravity, not needed.
Normal rice + GA spray
no effects; normal plants prod. GA, only dwarf plants would be affected.
Does Ga act as enzyme or coenzyme to activate? Does it turn on a gene to transcribe A-amylase
GA stimulateds transcription of A-amylase.
composite model for induction of A-Amylase synth in barley alalerurone layers.
Ca independent patheway; induces transcription of A-amylase gene
Induction of A-amylase: 1. GA 1 (from embryo) binds to cell surface receptor
2. GA receptor complex interacts with heterotrimeric G-protein, initiates 2 separate signal transduction chains.
3. CA independent pathway involving cGMP, results in activation of signaling intermediate (GA signal)
4. Signal intermed. Binds to DELLA repressor protiens in nucleus
5. This degrades DELLA repressor, making it inactive
6. MYP gene expression (& other genes) can be transcribed & translated
7. New MYB protein enters nucleus, binds to A-amylase promoter gene & otro hydrolytic enz
8. Activates transcription of amylase & otro hydro enz genes
9. Synthesis of above genes in ER
10. Golgi secretes above proteins
11. GA stimultn reqrd via CA-calmouldin-dependent signal transduction pathway

A-Amylase secretion is Ca dependent
bioassay of auxin
coleoptile straight growth test 1. Used living tissue to detect small amounts and measure----> Cells not tips contain IAA , cell elongates
bioassay of cytokinin
radish seed cotyledon expansion bioassaay performed in lab ???
ways to control auxin
One way plants can control the amount of IAA present in tissues at a particular time is by controlling the biosynthesis of the hormone

Another control mechanism involves the production of conjugates which are, in simple terms, molecules which resemble the hormone but are inactive.
how are conjugates important to auxin
The formation of conjugates may be a mechanism of storing and transporting the active hormone

Conjugates can be formed from IAA via hydrolase enzymes.
Conjugates can be rapidly activated by environmental stimuli signaling a quick hormonal response