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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

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slide1

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.

other uses of pulsing pgrs
Other uses of pulsing PGRs
  • Cut foliage
  • Seed germination
  • Rooting of cuttings
  • Spraying for various reasons
brassinosteroids
Brassinosteroids

Brassinolide

slide11

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)

slide15
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

slide16

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

slide17

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
Salicylic acid (SA)

Some roles include:

Induction of flowering

Thermogenesis regulation

Well-characterized role in disease resistance

(Hypersensitive response and Systemic Acquired

Resistance)

sa is important for local defense responses
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

slide26
Initial pathogen infection may increase resistance to future pathogen attack through development of SAR
actigard
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
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)
slide33

Polyamines

Putrescine

Spermidine

  • Promotes:
  • adventitious root formation
  • somatic embryogenesis
  • shoot formation
slide34

Strigolactones

  • Inhibit branching
  • Stimulate seed germination
  • in parasitic plants (Striga)
  • Signal for mycorrhizal interactions
slide36

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

slide37

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

37

leaves produce a chemical signal termined 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
slide41

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