Hormones and Adventitious root formation Flashcards
ABA and rooting
Inhibits rooting. Used in combination with auxin can promote rooting in some species.
ABA is naturally occurring and is most important for controlling stomatal opening during drought stress and during seed development.
ABA application can increase
rooting possibly by countering
the negative impact of
gibberellin.
Benzyladenine (BA)
Synthetic cytokinin that elicits plant growth and development and development responses, setting blossoms and stimulating fruit richness by stimulating cell division.
Charles Hess
Detected “rooting cofactors” from extracts of juvenile from of English Ivy. (increased root formation)
Cofactors
Actual compounds that may be cofactors: ABA, Phenolics.
Rhizocaline. Plant growth regulator effects. Auxin promotes rooting but is only one of a number of
factors needed to induce rooting.
Conjugation of auxin
Conjugation Indole-3-acetic acid (IAA)
of IAA protects
it from decarboxylation.
Conjugation adds a sugar or
an amino acid to the
carboxyl end of the
molecule.
The conjugated form can be
metabolized back to active IAA
Cytokinins and rooting
Important in shoot
initiation.
Tends to be inhibitory
to rooting.
Ratio of auxin to cytokinin is important in determining whether tissue cultures initiate roots or shoot
Dilute soak
Older procedure, bundle placed in diluted Auxin solution.
Ethephon
Ethylene (applied as ethephon)
is used to prevent flowering
and increase branching is some
stock plants.
Ethylene application can increase
rooting in some cuttings.
It is applied as ethephon.
Ethylene (and auxin induced
ethylene) inhibits root elongation.
Rooting is reduced in ethylene
mutants in tomato
Ethylene and rooting
Ethylene is the gaseous hormone.
It is always produced when auxin
is added to plant tissue.
Ethylene disrupts polar auxin
transport.
Therefore, it is difficult to
separate the auxin and ethylene
effects on rooting.
Gibberellins and rooting
There are over 100 naturally occurring gibberellins.
GA1 , GA3 , GA4 , GA7 are most widely occurring types of gibberellins.
GA3
is gibberellic acid and is the natural product of a
rice pathogenic fungus.
Developing seeds have the
highest concentration of
gibberellins in the plant.
Gibberellins are present in
the shoot, stem, leaves and
roots of plants.
Gibberellin is generally
inhibitory to rooting.
Hormone conjugation
Conjugation Indole-3-acetic acid (IAA)
of IAA protects
it from decarboxylation.
Conjugation adds a sugar or
an amino acid to the
carboxyl end of the
molecule.
Hormone spray application
Foilage. Until solution drips from leaves. 500-5000ppm. K-IBA aqueous. Effective reduces labor and time. Effective on certain species.
IAA-oxidase
IAA-oxidase removes the
carboxyl group (COOH) making
it ineffective as an auxin.
IAA
IAA is not used commercially
as often as synthetic auxins.
This is because it is not as
stable.
IAA degrades in the light and
is susceptible to destruction in
the plant by IAA-oxidase.
IAA-oxidase removes the
carboxyl group (COOH) making
it ineffective as an auxin.
IBA
Naturally occurring
Usually combined with NAA for better rooting performance.
The natural conjugates of auxin are not used commercially because they are expensive and not more effective than free IBA or NAA.
There are synthetic aryl
esters and amides of IBA
that have been used.
2iP
The naturally occurring cytokinins include:
Isopentenyl adenosine (2iP)
Zeatin (Z)
K-IBA
IBA Water Soluble Salts root stimulation takes place all around the basal end of the cuttings.
Kinetin (KN)
The major synthetic cytokinins include:
Benzyladenine (BA) or Benzylaminopurine (BAP)
Kinetin (KN)
Molar Concentration
The number of active molecules in the concentration regardless of weight.
Palcobutrazol
Inhibitors of gibberellin biosynthesis. Paclobutazol - Bonzi
Parts per million (ppm)
Auxin concentration is calculated in either
Parts per million (ppm)
(ppm x volume) =desired ppm of new solution x volume needed for new solution.
ex:
10,000 x vol= 250 x 1000ml
10,000/1,000 x= 250,000/1000
Volume (ml)= 25mL
Phenolics
Phenolics act to protect
auxin from destruction by
acting as an alternative
substrate for IAA-OXIDASE.
Polar auxin transport
Polar auxin transport Root / Shoot Junction Proximal Distal Proximal Auxin is produced in the Distal apical meristems.
Auxin transport is polar.
It moves from distal to
proximal.
Quick dip
Submerse bottom of cutting into solution 3-5 seconds. 500-10,000ppm. Usually 50% solvent (ethanol) potassium salts in water. Most uniform and effective way to treat cuttings.
Rhizocaline
Theoretical compound that may be the answer to why a plant may not root.
The German plant physiologist, Julius Sachs (1880’s) felt
that there were specific root forming substances made in
the leaves that moved to the base of cuttings to promote
rooting.
Fritz Went in 1938, again postulated the existence of this
substance and termed it rhizocaline.
Rooting including bacteria
Nitrogen-fixing bacteria.
Rooting cofactors (auxin synergists)
Any of a group of hormones that regulate plant growth, particularly by stimulating cell elongation in stems and inhibiting it in roots. Auxins influence the growth of stems toward light (phototropism) and against the force of gravity (geotropism). Auxins also play a role in cell division and differentiation, fruit development, the formation of roots from cuttings, the inhibition of lateral branching, and leaf fall. The most important naturally occurring auxin is beta-indolylacetic acid.
Talc treatment
Common treatment. Base of the cutting isolated with Auxin. 0.1-8.0% concentration. Talc is the most common carrier. Herbaceous cuttings, easiest to use, not as much uniformity, no need for preparation need to wet the base of cuttings. Pre-dip in ethanol better rooting performance.
Zeatin (Z)
The naturally occurring cytokinins include:
Isopentenyl adenosine (2iP)
Zeatin (Z)
NAA
Synthetic -Naphthalene acetic acid (NAA)
is a purely synthetic auxin.
It is chemically similar to IAA in
structure but is a more effective
auxin in promoting rooting.
It is commonly found in
commercial rooting compounds
and is often combined with IBA.
2,4-D
Synthetic. Tissue culture to stimulate somatic embryo-genesis.
