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“Hormone” was first used to describe substances in animals:

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Presentation on theme: "“Hormone” was first used to describe substances in animals:"— Presentation transcript:

1 “Hormone” was first used to describe substances in animals:
“a substance produced in a gland that circulates in the blood and has an effect far away from the site of production” In plants used to mean a compound that acts at low concentrations to affect growth and development. Produced in one part of the plant and utilized in another part.

2 Five plant hormones known by the mid 1960s, new compounds called plant growth regulators.
The five classical hormones Auxins Cytokinins Gibberellins Ethylene Abscisic acid Other plant growth regulators Brassinosteroids Salicylic acid Jasmonic acid Systemin Florigen

3 Hormones Class Endogenous Hormone Growth Regulators
auxin indoleacetic acid IBA, NAA, 2,4-D, others cytokinin zeatin, zeatin riboside kinetin, BA, 2iP, TDZ gibberellin GAx GA3, GA4+7 abscisic acid abscisic acid (ABA) ethylene ethylene Ethephon, Ethrel


5 Frits Went’s experiments





10 Auxin (indoleacetic acid)
Produced in apical and root meristems, young leaves, seeds in developing fruits cell elongation and expansion suppression of lateral bud growth initiation of adventitious roots stimulation of abscission (young fruits) or delay of abscission hormone implicated in tropisms (photo-, gravi-, thigmo-)

11 Auxin Indole acetic acid and related molecules Photo-and gravitropism
The shoot hormone, made in the shoot apex Travels down the stem Polar Auxin Transport


13 Auxin promotes rooting

14 Auxin also: Promotes apical dominance Prevents leaf abscission
Enhances fruit growth Auxin from the developing seeds results in fruit growth


16 Auxin-like growth regulators
indolebutyric acid (IBA) 2, 4 dichlorphenoxyacetic acid (2,4D) 2, 4, 5 trichlorophenoxyacetic acid (2, 4, 5 T) picloram

17 Napalm, Agent Orange, dioxin

18 Herbicide 2,4-D – 2,4 dichlorophenoxy acetic acid
Causes a plant to grow itself to death More readily absorbed by broad-leaved plants Most often the “weed” of ‘Weed and Feed’ lawn fertilizers


20 Commercial uses - auxins
stimulation of adventitious rooting 2,4-D as a herbicide for dicots sprout prevention in pruned trees fruit thinning or fruit holding depending on stage of development

21 Cytokinin Cytokinin – the root hormone Discovered by Folke Skoog
The last unknown compound needed to get plant cells to grow undifferentiated Cytokinins delay and even reverse senescence Release buds from apical dominance

22 Cytokinin (zeatin, ZR, IPA)
cell division factor stimulates adventitious bud formation delays senescence promotes some stages of root development

23 Cytokinins Cell division and cytokinesis - Moves in xylem sap
- Stimulates RNA and protein synthesis - Works in conjunction with auxin b. Apical dominance - Cytokinin and auxin are antagonistic- auxin from terminal bud causes shoot to lengthen - Cytokinins from roots stimulate axillary bud -Auxin stimulates lateral root formation cytokinins restrain it - Anti-aging - slows leaf deterioration

24 Commercial uses - cytokinins
Applied as kinetin, benzyladenine, or zeatin conjugates axillary bud growth in orchids, daylilies antioxidant (browning preventer) in cut salads mix with GAs as fruit size stimulator


26 Gibberellins A large family of compounds (80) with a few biologically active members Produced in roots and young leaves Now known to be essential for stem elongation Dwarf plant varieties often lack gibberellins

27 Gibberellins Found as the toxin produced by some fungi that caused rice to grow too tall – “Foolish Disease” Induces parthenocarpic fruit development Delays senescence

28 Gibberellins are involved in bolting of rosette plants
Gibberellins are used to improve grapes Gibberellins are involved in seed germination gibberellins will induce genes to make enzymes that break down starch

29 Commercial uses - GA inhibitors
Cycocel, Bonsai, Sumagic height control in flowering pot plants (lilies, orchids) height control in bedding plants

30 Commercial uses - GA application
Apply as GA3, or GA4+7 increase flower size on certain ornamentals (eg, “gibbing” camellias) increase berry separation and size in bunch grapes overcome shallow dormancies in vegetative buds stimulate seed germination


32 Ethylene The smallest hormone A gas
Important in seed germination, fruit ripening, epinasty, abscision of leaves Sex expression in cucurbits

33 Ethylene Gaseous hormone produced in many plant tissues
autocatalytic (stimulates its own production) volatile gas production stimulated during ripening, flooding, stress, senescence, mechanical damage, infection product of combustion of petrochemicals


35 Commercial uses - ethylene application
Applied as ethylene gas or Ethephon or Ethrel sprays flower initiation (bromelliads, pineapples) stimulation of ripening (bananas, tomatoes) degreening of citrus abscission induction prior to mechanical harvest (cherries) increased color development in once-over harvested processor type tomatoes

36 Commercial uses - ethylene inhibition
Removed by chemical “scrubbing” or low atmosphere long term storage of apples in CA storages treatment of cut flowers with silver thiosulfate long-keeper (delayed ripening) mutants (or rDNA) of tomato hypobaric storage of many fruits, vegetables, flowers


38 Abscisic acid (ABA) Found in stressed leaves, dormant seeds, dormant buds stomatal closure inhibits germination of some seeds inhibits active growth of axillary buds

39 Abscisic acid Incorrectly named, not related to abscission
Important in water stress and other stresses Causes stomatal closure Prevents premature germination of seeds Changes gene expression patterns








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