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MCDB > Plant Growth and Development > Flashcards

Plant Growth and Development Flashcards

1
Q

Phytohormones

A

classical: discovered at least 50 years ago, small molecules, can cross membrane in uncharged form, all have many effects in all stages of life cycle and in many tissue/cell types, there are both postitive and negative interactions among hormones (5: 1AA, GA, CK, ABA, ethylene)
new: discovered in last 25 years, lipid, oligosaccharide, steriod and peptide

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2
Q

Hormone responses

A

requires: biosynthesis, arrival at site of action, recognition, transduction
diversity of responses refelcts diversity of signaling mechanisms
perception or signaling may involve more than one receptor or pathway

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3
Q

Hormone recognition

A

can be intra or extracellular: most plants can cross cell membrane but dont have to
recognition at cell surface can reach nucleus through phosphorylation cascade or by G-protein and secondary messengers

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4
Q

Secondary messengers

A

IP3 and Ca2+

concentrations change rapidly and transiently

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5
Q

Brassinosteroid receptor

A 
receptor for steroid hormones
membrane bound (rather than cytoplasmic as in animal cells)
chemical similarity of hormones not relected in signaling mechanism
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6
Q

Ways to study hormone response

A
  • physiological: spray and prey: spray hormone and pray for a response then catalog
  • genetic: wreck and check: indentify the genes required for a response, identify the responses requireing common signaling factor, analyze biochemical function following cloning
  • reverse genetics: create specific mutations to determine physiological function fo gene product with known biochemical function
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7
Q

Embryogenesis

A

forms mini-plant
occurs within many layers of maternal tissue
1AA = auxin - pattern formation
CK = cytokins - cell division
GA = gibberellins - nutrient uptake and cell growth

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8
Q

Embryo

A

mini-plant encased in endosperm and maternal tissue

1n (egg) + 1n (sperm)

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9
Q

Endosperm

A

2n (polar nuclei) + 1n (sperm)

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10
Q

auxin (1AA)

A

pattern formation
directional transport creates gradients that drive embryonic pattern formation
overproduction in some seedless fruits
required for polarity and histodifferentiation of early embryo
promotes bending for phototropism by laterally redistributing due to light and gravity
promotes unequal elongation in tropic growth

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11
Q

Endosperm reserves

A

stored in seeds in endosperm
may be protein, lipid or starch
may be consumed during embryogenesis or after germination depending on the species

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12
Q

Seeds

A

development takes place within layers of maternal tissue

edible fruits aid seed dispersal

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13
Q

Ethylene

A

may stimulate ripening of fruit
induces triple response
synthesis induced by pressure and is autocatalytic and inhibided by light
alters orientation of cellulose microfibril depostition
can cross plama membrane easily sinse its receptor is in the ER

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14
Q

Cytokins (CK)

A 
cell division
with GA promotes nutrition of early embryo
with 1AA and GA promotes fruit growth
produced in roots, transported to shoots
inhibit senescence
growth-promoting substance
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15
Q

Gibberellins (GA)

A

nutrient uptake and cell growth
with 1AA and CK promates fruit growth
promotes germination and reserve mobilization
discovered due to “foolish seedling” disease: plants grew tall and spindly
over 130 different GA’s
19-20 C’s arranged in ring structure, all weak acids due to carboxyl group
GA deficient: dwarves
induces synthesis of anylase and other hydrolases in embryoless half seed or isolated aleutone
effects transcription, translation and secretion
induces gene expression by destruction of repressor via proteasome

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16
Q

ABA

A

promotes reserve accumulation, dormancy, desiccation tolerance
with GA and ethylene controls germination
implicated in stress tolerance and limiting growth
promotes embryo maturation by inhibiting germination = delays flowering
promotes stress tolerance by inhibiting cell elongation and cell division
controls stomatal closure, senescence, and accumulation of desiccation protectants
promotes root elongation under mild stress, but inhibits under severe stress
inhibits lateral root initiation
not plant specific (in some fungi, parasites etc)

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17
Q

Germination

A

requires reserve mobilization to support growth until seedlings are photosynthetically active
promoted by GA

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18
Q

Amylase

A

needed to digest seed reserves

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19
Q

GA in the aleurone

A
  • perceived at cell surface and in nucleus
  • signaling involves g-protein action through 2 separate pathways
  • Ca2+ and cGMP act as secondary messengers
  • Inductionof gene expression requires destruction of repressor and synthesis of positive regulator
  • Ca2+ also promotes secretion
  • process is antagonized by ABA
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20
Q

Immature seeds

A

GA levels low and ABA levels are high during embryo maturation so immature seeds dont degrade the reserves
embryos are not sensitive to GA until seed maturity

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21
Q

Triple response

A

radial swelling of seed
maintains apical hook
agravitropic growth (grow in direction opposite gravity)
this response is for the emergence of plant from soil
ethylene induces this response

22
Q

radial swelling

A

part of triple response
short wide stems have shore wide cells
ethylene alters orientation of cellulose microfibril depostition

23
Q

Ethylene receptors

A

related to 2-component regulators
family of closely related proteins containing one or both parts of 2-component system
defect in one gene produces a never ripe mutant
conserved domains mediate interations between senso and response regulators
input and output domains vary

24
Q

Mechanism of ethylene signaling

A
  1. ethylene binds to receptor
  2. ethylene and receptor block activation of repressor (CTR1)
  3. permits promotion of ethylene responses by EIN2 and EIN3
    when ethylene binds, CTR1 is deactivated so that genes can be expressed
    ligand binding inactivates
25
Q

MAPK

A

mitogen activated protein kinases
kinase kinase controls ^
kinase kinase kinase controls ^

26
Q

De-etiolate

A

light induced preparation for autotrophic growth (photosynthetic growth)
leaves expand
stem elongation is inhibited
chloroplasts develop thylakoid stacks
genes required for photosynthesis and other light-dependant processes induced

27
Q

Blind mutants

A

have lost positive regulators of light response

have long hypocotyls

28
Q

DET mutants

A

constitutively de-etiolated

have lost negative regulators of light response or positive regulators of etiolated growth

29
Q

Brassinosteroid

A

promote extreme elongation growth and inhibits plastid differentiation in the dark
interacts postively with auxin and GAs, negatively with ABA
brassinosteroid synthesis increases when plants are maintained in the dark, resulting in etiolated growth

30
Q

Brassinosteroid signaling

A

receptor complex is embedded in the plasma membrane (recognized at cell surface)
without binding, phosphorylation events that inhibit repressor kinase occur (genes are repressed)
when it binds dephosphorylation alters stability and gene expression (derepression)
This same receptor also works for systemin and auxin signaling

31
Q

Phototropism

A

light is sensed at the tip, and it grows more effectively towards blue light

32
Q

Source and transportation of auxin

A

synthesized in rapidly growing parts of plants
movement is always from tip to roots regardless of plant orientation to gravity
lateral redistribution for phototropism
carrier mediated, metabolic energy required for transportation

33
Q

Chemiosmotic polar auxin transport

A

3 parts:

  1. pH ggradient across plasma membrane - cell acts as an anion trap
  2. carrier-mediated auxin uptake - lateral redistribution
  3. basally localized efflux carriers - confer polarity
34
Q

Auxin and cell elongation

A

at least 2 processes

  1. rapid: wall loosening (increased plasticity)
  2. long-term effects: continued wall and membrane synthesis
35
Q

Acid growth hypothesis

A

explains rapid effects due to auxin
auxins promote H+ secretion causing wall pH to derease
low pH activate proteins that disrupt bonds between polysaccharides
microfibrils can slide past each other in loosened wall and the cell can expand if there is sufficient turgor pressure

36
Q

Long-term effects of auxin

A

require auxin-induced gene expression
ABP1 (auxin binding protein) acts at plasma membrane
distinct soluble receptors indirectly regulate transcription factor activity

37
Q

Genetic approach to auxin response

A

auxin promotes

  • embryonic pattern formation
  • root meristem formation and grwoth
  • vascular differentiation
  • lateral organ initiation
  • cell elongation
  • apical dominance
38
Q

Auxin response mutants

A

many have defects in targeting proteins for degradation
protein degradation involves tagging proteins with ubiquitin which targets them to proteasome
auxin induced gene expression is normally repressed so in order to express auxin gene the degradation of repressors needs to occur

39
Q

Auxin-induced elongation

A

tropic response requires asymmetric redistribution of auxin (phototropism, gravitropism)
-H+ pump used for chmiosmotic mechanism of transport and creating a pH gradient for wall loosening

40
Q

Lateral organ initiation

A

depends on auxin gradients established by auxin transport
auxin transported by PIN1 proteins (eflux carriers)
apical dominance results from auxin produced by the apical bud

41
Q

Branching

A

controled by auxin, cytokinin and strigolactones
shoot branches: promoted bby CK and inhibited by auxin and strigolactones
root branches (lateral roots): promoted by auxin and inhibited by CK
branching controls every aspect of plant productivity from nutrient uptake to crop yields

42
Q

Totipotent

A

can regenerate entire plant from any live cell given the right combination of growth regulators
plant cells are totipotent

43
Q

Plant organogenesis

A 
controlled by auxin/cytokinin balance
auxins produced in shoots
cytokinins produced in roots
ratio reflects balance of source tissues
(low CK/AA ratio = more roots, high ratio = more shoots)
44
Q

Senescence

A

degradation of macromolecules and exportation of nutrients to rest of plant before falling off (leaves)
inhibited by cytokinins and induced by ethylene and ABA

45
Q

Cytokinin receptors

A

2-component receptor superfamily

signaling involves kinase cascade

46
Q

ABA deficient mutants

A

wilty, stunted and can be viviparous because they can’t protect themselves in times of stress (lose water on hot days because they cant close stomata)

47
Q

ABA signaling during stress

A

transportation of existing ABA is through shoot transpiration stream to target tissue (guard cells)
synthesis of new ABA
stomatal closure (involves g-proteins and usual scondary messengers)
changes in gene expression
receptors both inside and outside the plasma membrane
3 classes of receptors (one or more pathways act by derepression)
involves phosphorylation cascades, trascriptional controls and positve and negative regulators

48
Q

ABA in other organisms (besides plants)

A

produced by some fungi, unicellular parasites and metazoa ranging from sponges to mammals
livolved in parasite pathogenicity, igh temperature regulation of water filtration in sponges, regerneration of body parts by hydroids, immune response in humans
conserved signaling intermediates include G proteins, reactive oxygen species, nitric oxide, cADPR and Ca2+
understanding of biosynthetic pathway and signaling mechanism from studies with plants can be exploited therapeutically

49
Q

hormone synthesis (overview)

A

all synthesized in many tissues at many stages

50
Q

Hormone distribution (overview)

A

controlled by a combination of synthesis, transport, and inactivation (by conjugation or degradation)
intra- vs. extracellular partitioning controlled by pH and specific carriers

51
Q

Hormone perception (overview)

A

many perceived at cell surface even though they are membrane soluble
some also perceived intra-cellularly
multiple receptors identified for several hormones

52
Q

Hormone signaling (overview)

A

lots of cross-talk among pathways, including positive and negative interaction
effects of a given hormone vary among different parts of the plant
responses are amplified by enzyme cascades, effects on multiple levels of regulation, and a combination of turning on activators and inactivating repressors
some plant-specific signaling mechanisms, but many highly conserved signaling components are used
signals and responses change as needed, same ancient signaling mechanisms used for transduction

MCDB (5 decks)

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