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Plant Hormones Flashcards

1
Q

Phytohormones

A

Chemical messengers that mediate intercellular communication in very small quantities

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2
Q

Function of phytohormones

A

Control plant growth and development by affecting the division, elongation and differentiation of cells
Regulate reproduction, sex determination and responses to abiotic and biotic stresses

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3
Q

Types of phytohormones

A

Auxin
Cytokinins
Gibberellins
Abscisic acid
Ethylene

Brassinosteriods
Salicylates
Strigolactones
Jasmonates

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4
Q

Auxin

A

First hormone discovered, characterised in 1926
Indole-3-acetic acid (IAA) is the most common and active:

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5
Q

Location of auxin

A

All tissues
Mostly associated with rapidly dividing and growing tissues, especially in shoots (meristems, leaves and developing fruits)

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6
Q

Transport of auxins

A

Actively transported polarly (transport proteins)

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7
Q

Roles of auxins

A

Plant growth (cell elongation)
Root formation
Fruit development
Apical dominance
Lead abscission
Tropisms

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8
Q

Cell elongation

A

Auxin stimulates H+pump
H+ pumped from cytoplasm into cell wall
Causes expansins to loosen cellulose and elongate cell wall
Water moves into permanent vacuole and cell elongates

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9
Q

Root initiation

A

When a leaf is excised from a plant, auxin produced by the leaf accumulate in the wound and in the absence of cytokinin from the root, cause the plant to form roots

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10
Q

Tropisms

A

Directional growth response

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11
Q

Phototropism

A

Elongation of cells on the shaded side
Triggered by blue light
IAA molecules concentrate on shaded side of plant

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12
Q

Gravitropism

A

Plant detects gravity with statoliths (specialised plastids containing dense starch grains)
Aggregation of statoliths cause redistribution of calcium which ceases lateral transport of auxin within the root
Cytokinin distribution controls the growth
Higher concentration of auxin in lower side of root inhibits growth

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13
Q

Thigmotropism

A

Growth response to contact with a solid object
Touched cells produce auxins that are transported to untouched cells

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14
Q

Apical dominance

A

Inhibitory control by the apical portions of the shoot over the growth of the lateral buds below

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15
Q

Cytokinins

A

Discovered in the 1930s to promote cell division, vital for plants
Adenines with N6 on isoprene-derived side chain (greater abundance) or aromatic derivative side chain (less abundant)

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16
Q

Location of cytokinins

A

Synthesised mostly in the root
But also in shoot apical meristems, Axillary buds and young leaves

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17
Q

Transport of cytokinins

A

From the root to the shoot in the xylem

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18
Q

Roles of cytokinins

A

Cell division and differentiation
Leaf senescence
Nutrient mobilisation
Modify apical dominance
Bud dormancy
Seed germination
Delay leaf senescence

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19
Q

Cell division and organogenesis

A

High cytokinin = shoot formation
High auxin = root formation

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20
Q

Delay of leaf senescence

A

(selective removal of nutrients and organic compounds from an organ followed by death):
CKs are produced in young leaves and act to identify them as sinks for sugars and amino acids.

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21
Q

Gibberellins

A

First isolated from the fungus Gibberella fujikuroi, which causes excessive shoot elongation
Tetracyclic diterpenes, 136 types characterised (GA1 – GA136). Most are biologically inactive

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22
Q

Location of gibberellins

A

Meristems of apical buds and roots
Young leaves
Developing seeds
Developing anthers and pollen

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23
Q

Transport of gibberellins

A

Passive diffusion in the xylem and phloem

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24
Q

Roles of gibberellins

A

Stem elongation and leaf growth
Parthenocarpy
Flowering
Pollen development and growth
Seed germination
Sex determination

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25
Gibberellins- cell division and elongation
In the intercalary meristem at the base of the internode
26
Parthenocarpy
Auxins and gibberellins induce parthenogenesis (fruit production without fertilisation) Eg seedless tomatoes, grapes
27
Ethylene
Discovered in 1901 by a Russian graduate student Simple molecule, gas
28
Location of ethylene
Almost all parts of plants
29
Transport of ethylene
Simple diffusion gas
30
Roles of ethylene
Fruit ripening Leaf abscission Epinasty Growth promotion Hook opening Seed and bud dormancy Induction of roots Flowering Flower and leaf senescence
31
Fruit ripening
in climacteric fruits, there is an increase in respiration and ethylene synthesis which produces chlorophyll to be degraded and other pigments to form. Simultaneously, there is enzymatic degradation of pectin, softening the flesh, and starch and organic acids are transformed to sugars.
32
Abscisic acid
First isolated as a growth-inhibiting compound in early 1950s, thought to be responsible for organ abscission Widely distributed in nature, ubiquitous in plants, found in mosses and fungi
33
Location of Abscisic acid
Almost in all plant cells Synthesised in the plastids
34
Transport of Abscisic acid
Through xylem and phloem
35
Roles of Abscisic acid
Bud and seed dormancy Growth inhibition Stress and stomatal closure Water uptake Abscission and senescence Protein synthesis
36
Stomatal closure
Abscisic acid creates rapid changes in the osmotic potential of guard cells Guard cells release K+ and Cl- and water exits, loosing turgor and thus closing
37
Roles of Salicylic acid and salicylates
Flowering induction Senescence Disease resistance
38
Jasmonates
Discovered in the 1970s Derived from fatty acids
39
Roles of Jasmonates
Inhibition of growth Flower development Defense responses against herbivores and fungal pathogens
40
Brassinosteriods
Plant steroids, first discovered in the 1960s Present in all plant tissues More than 40 identified: C27, C28 and C29 steroids with different functional groups on the A- and B- rings and side chain
41
Roles of Brassinosteriods
Stem elongation Pollen tube growth Unrolling grass leaves Ethylene production
42
Strigolactones
First discovered in the 1960s as Striga seed stimulants Functional roles in plants discovered in 2005!
43
Roles of Strigolactones
Stimulation of germination of parasitic plant seeds Induction of hyphal branching of arbuscular mycorrhizal fungi Inhibitor of shoot branching
44
Epinasty
the downward turn of leaves when the upper part of petioles grows faster than the lower part
45
Abscission vs senescence
Abscission is the process by which plant components such as flowers, fruits, and leaves naturally separate from the parent plant. Senescence is a state of biological aging in which cells cease to divide and enter a cell cycle arrest phase.
46
Methods of cell communication
Apoplastic Via vacuoles Symplastic (cytoplasm and plamodesmata)
47
Apoplast
Interconnected cell walls
48
Symplast
cytoplasmatic continuum connecting neighbouring cells via plasmodesmata (channels allowing cytosol to pass but not organelles)
49
Reception of ethylene
Small, lipophilic molecules can cross the lipidic bilayer membrane and be perceived in the cytoplasm or nucleus. E.g. ethylene is perceived in the endoplasmic reticulum. CTR1 protein Cofactor = Cu 2+ Without ethylene, CTR1 binds into the receptor and prevents transcription of ethylene responsive With ethylene, ethylene binding releases CTR1, permitting transcription: genes:
50
Apoplastic transmission
Associated with the transmission of plant hormones and signal peptides via receptor proteins: Receptor kinases: largest group, transduce signals via phosphorilation (transfer of phosphate groups): e.g. CKs. G protein-coupled receptors: regulate trimeric GTP-binding proteins (G proteins). Unknown roles. Ion channel receptors: regulate ion channel fluxes into or out of the cell. E.g. Ca2+
51
Symplastic reception
allows regulated movement of RNAs and transcription factors proteins.
52
Cytokinin transduction
involves a two-component system: a histidine kinase and a response regulator in addition to an intermediate protein: CK activates phosphorylation and once the intermediate protein is phosphorylated, it enters the nucleus and transduction occurs.
53
Histidine kinase
Input domain Transmitter domain
54
Auxin transduction
influx occurs by passive diffusion and by active transport via LAX proteins, and efflux via PIN proteins:
55
What do hormones mediate in angiosperms
Plant growth: - Seed dormancy and germination Reproductive development: Transition from vegetative to reproductive growth Flower development Fruit development and ripening Seed development and maturation Stress response
56
What external factors does germination depend on
Water: many seeds must imbibe water to start metabolic activities Oxygen: to start oxidising glucose to obtain energy Temperature: for metabolic processes to start
57
Dormancy
some seeds do not germinate even with favorable conditions. They need to break dormancy to germinate. Physical (impermeable seed coat): High/fluctuating temperatures Fire Freezing/thawing Physiological (chemicals that prevent germination): Water uptake Deactivation by other means
58
Photoperiodism
Effect of light on flowering Length of the dark period is used to decide when to flower
59
Circadian rhythms
regular, approximately 24-hour cycles, present in most organisms, from cyanobacteria to land plants and animals Stomatal opening Leaf movement Growth Metabolism Induction of flowering Response to stress… Controlled internally by a biological clock, synchronised by external stimuli.
60
Consequences of stress
Inhibition of growth, cell division, changes in cell wall synthesis Inhibition of shoot growth and stimulation of root growth (increase of the root/shoot ratio) Acceleration of aging Accumulation of osmotically active compounds (proline, glycinebetaine, sugars, sugar alcohols) ROS production and development of antioxidative systems Inhibition of photosynthesis, transport of assimilates, respiration Changes in enzyme activities, hormone production Changes in absorption and transport of ions
61
Heat stress
excessive heat harms and can even kill a plant by denaturing enzymes and damaging metabolism. Transpiration: evaporative cooling. Water control! Production of heat-shock proteins: help protect other proteins
62
Herbivory
plants are attack by many animals but they defend themselves with: Physical defenses: hairs, spines, thorns… Chemical defenses: secondary metabolites
63
Induced defence
not only in the part being attacked but also in other parts of the same plant (Systemic Acquired Resistance, SAR): Salicylic acid (SA) Jasmonates (JA) Ethylene
64
Which hormone levels are relatively stable during seed Morphogenesis, maturation and desiccation
Auxins Cytokinin BR
65
How do gibberellins levels change during seeds
Increase = Morphogenesis Decreases = maturation Increases = desiccation
66
How do Abscisic acid levels change during seeds
Decrease = Morphogenesis Increase = maturation Maintained = desiccation
67
Which hormone breaks dormancy of seeds
Gibberellins
68
Hormones involved in seedling establishment in dark
Gibberellins Auxins
69
Hormones involved in seedling establishment in light
Auxins Ethylene Gibberellins BRs
70
Phytochrome
Darkness (light) is sensed by the phytochrome

Plant Structure And Function (13 decks)

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