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

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 > 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 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 Putrescine Spermidine Promotes: adventitious root formation somatic embryogenesis shoot formation Promotes: adventitious root formation somatic embryogenesis shoot formation

Strigolactones 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

Florigen

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)

37 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

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 : ; doi: /pcp/pcn154 A current model of the action of the FT florigen