Pulsing Hormones

When cultured material is exposed to a substancefor only a short period of time, it is frequently said tohave been given a pulse of that substance or regulant.

Sometimes a pulse of a growth regulator at arelatively high rate can be as effective as a lowerconcentration, which is present continuously.

Somatic embrygenesis in potatoSomatic embrygenesis in potato

Somatic embrygenesis in potatoSomatic embrygenesis in potato

Other uses of pulsing PGRs

• 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 sterioidCL, campesterolCT, cathasteroneTE, teasteroneDT, 3-dehydroteasteroneTY, typhasterolCS, castasteroneBL, 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 AcquiredResistance)

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

bindingXyloglucan – e.g. hemicellulose - derived polymers • Stimulates: cell elongation and growth defense responses

morphogenesis (in culture)

 

Production of oligosaccharins during fungal invasion

PolyaminesPolyamines

PutrescineSpermidinePutrescineSpermidine

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

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

StrigolactonesStrigolactones

•Inhibit branching•Stimulate seed germination

in parasitic plants (Striga)•Signal for mycorrhizal interactions

•Inhibit branching•Stimulate seed germination

in parasitic plants (Striga)•Signal for mycorrhizal interactions

FlorigenFlorigen

FT is a floral activator both in LD and SD plants

Long Day Plant Short Day Plant

CO in Long Day plants and similar proteins in Short Day plants are regulated in opposite ways

(Kobayashi & Weigel, 2007)

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• the flowering signal is generated in the leaf

• the signal goes one way: from the leaf to the apex

• Grafting transmittable

The flowering signal: florigen

?

vegetative or reproductive growth?

SAM

Florigen

Florigen

Florigen

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

Notaguchi, M. et al. Plant Cell Physiol. 2008 49:1645-1658; doi:10.1093/pcp/pcn154

A current model of the action of the FT florigen