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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.
Somatic embrygenesis in potato
Somatic embrygenesis in potato
Other uses of pulsing PGRs
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Cut foliage
Seed germination
Rooting of cuttings
Spraying for various reasons
Other Growth Regulators (Hormones?)
Brassinosteroids
Brassinolide
Discovery of Brassinosteroids
Discovered as a growth stimulator from pollen extracted from rape plant
(Brassica napus L.) -> Mitchell et al. 1970 -> called substances Brassins
Occur in Brassicaceae (mustards, cauliflowers, cabbages, turnips, Arabidopsis)
Brassins induced stem elongation in beans: Mandava 1988
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
Brassinosteroid-mediated physiological
responses
Inhibit:
-Root growth (but also promote root growth)
-Leaf abscission
Stimulate:
-Cell and stem elongation and division -> promote shoot
growth
-Unrolling and bending of grasses
-Ethylene production
-Seed germination and Photomorphogenesis
-Xylem differentiation
-Pollen tube growth
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
Salicylic acid (SA)
Some roles include:
Induction of flowering
Thermogenesis regulation
Well-characterized role in disease resistance
(Hypersensitive response and Systemic Acquired
Resistance)
Salicylic acid (SA)
SA induces the expression of
pathogenesis-related (PR) proteins
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
SA is also important for defense in
distal parts of the plant (systemic
responses)
(SAR)
Initial pathogen infection may increase
resistance to future pathogen attack
through development of SAR
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
Oligosaccharines – stimulate defense responses
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)
Production of oligosaccharins during fungal invasion
Polyamines
Putrescine
Spermidine
Promotes:
•adventitious root formation
•somatic embryogenesis
•shoot formation
Strigolactones
•Inhibit branching
•Stimulate seed germination
in parasitic plants (Striga)
•Signal for mycorrhizal interactions
Florigen
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
The flowering signal: florigen
vegetative or
reproductive
growth?
• the flowering signal is
generated in the leaf
SAM
• the signal goes one way: from
the leaf to the apex
• Grafting transmittable
Florigen
Florigen
?
Florigen
37
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
A current model of the action of the FT florigen
Notaguchi, M. et al. Plant Cell Physiol. 2008 49:1645-1658; doi:10.1093/pcp/pcn154