Pulsing Hormones

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Pulsing Hormones
When cultured material is exposed to a
substance for only a short period of time, it is
frequently said to have been given a pulse of
that substance or regulant.
Sometimes a pulse of a growth regulator at
a relatively high rate can be as effective as a
lower concentration, which is present
continuously.
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Somatic embrygenesis in potato
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Somatic embrygenesis in potato
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Other uses of pulsing PGRs

• Cut foliage
• Seed germination
• Rooting of cuttings
• Spraying for various reasons

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Other Growth Regulators (Hormones?)
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Brassinosteroids
Brassinolide
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Discovery of Brassinosteroids
Discovered as a growth stimulator from pollen
extracted from rape plant (Brassica napus L.) -gt
Mitchell et al. 1970 -gt called substances Brassins
Occur in Brassicaceae (mustards, cauliflowers,
cabbages, turnips, Arabidopsis)
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Brassins induced stem elongation in beans
Mandava 1988
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Brassinolide and intermediates of the BL
biosynthetic pathway restore normal growth to the
cpd mutant
no sterioid CL, campesterol CT,
cathasterone TE, teasterone DT,
3-dehydroteasterone TY, typhasterol CS,
castasterone BL, brassinolide
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Brassinosteroid-mediated physiological responses
Inhibit -Root growth (but also promote root
growth) -Leaf abscission Stimulate -Cell and
stem elongation and division -gt promote shoot
growth -Unrolling and bending of
grasses -Ethylene production -Seed germination
and Photomorphogenesis -Xylem differentiation -P
ollen tube growth
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Jasmonic acid (JA)
Inhibits -Seed and pollen germination -Root
growth Stimulates -Plant defenses against
microbial and insect pathogens -Wound responses
-Ripening -Exogenous application decreases
expression of genes associated with
photosynthesis
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Salicylic acid (SA)
Some roles include Induction of
flowering Thermogenesis regulation Well-charac
terized role in disease resistance
(Hypersensitive response and Systemic
Acquired Resistance)
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Salicylic acid (SA)
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SA induces the expression of pathogenesis-related
(PR) proteins
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SA is important for local defense responses
Resistance of Arabidopsis to Hyaloperonospora
parasitica (cause of downy mildew)
Nawrath et al. 1999 Plant Cell 11 1393
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SA is also important for defense in distal parts
of the plant (systemic responses)
(SAR)
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Initial pathogen infection may increase
resistance to future pathogen attack through
development of SAR
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Actigard

• Commercially available compound
• Activates plants for protection against a variety
  of pathogens induces SAR
• Minimal impact on beneficial insects
• Unique mode of action means resistance
  development is unlikely
• Designated by the EPA as a Reduced Risk Pesticide
  
• Low use rates

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Oligosaccharines stimulate defense responses
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Oligosaccharines

• Oligogalacturonides - pectin-derived polymers
• Stimulates flower formation defense responses
• Inhibits root formation
• Mode of action alters auxin formation or
  inhibits auxin binding
• Xyloglucan e.g. hemicellulose - derived
  polymers
• Stimulates cell elongation and growth defense
  responses morphogenesis (in culture)
•  

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Production of oligosaccharins during fungal
invasion
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Polyamines
Putrescine Spermidine

• Promotes
• adventitious root formation
• somatic embryogenesis
• shoot formation

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Strigolactones

• Inhibit branching
• Stimulate seed germination
• in parasitic plants (Striga)
• Signal for mycorrhizal interactions

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Florigen
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FT is a floral activator both in LD and SD plants
Long Day Plant
Short Day Plant
(Kobayashi Weigel, 2007)
CO in Long Day plants and similar proteins in
Short Day plants are regulated in opposite ways
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The flowering signal florigen
vegetative or reproductive growth?

• the flowering signal is generated in the leaf
• the signal goes one way from the leaf to the
  apex
• Grafting transmittable

SAM
Florigen
?
Florigen
Florigen
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Leaves produce a chemical signal termined
florigen

• This signal is transmitted to the apical meristem
  and the conversion to a floral meristem begins
• Have not completely identified the chemical
  nature of florigen
• One component is mRNA encoded by the gene
  FLOWERING LOCUS T (FT)
• FT protein translated from mRNA binds to and
  activates transcription factors in the nucleus of
  the meristem
• Activates LEAFY (LFY), which then turns on the
  expression of genes needed for flowering

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A current model of the action of the FT florigen
Notaguchi, M. et al. Plant Cell Physiol. 2008
491645-1658 doi10.1093/pcp/pcn154