plant growth regulators lecture note.ppt

Lecture note

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Photomorphogenesis
Morphogenesis:
development of plant organs –not directional.
e.g. photomorphogenesis:
developmental effects mediated by light

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Photomorphogenesis vs. Phototropism
Morphogenesis:
development of plant organs –not directional,
e.g. photomorphogenetic effects mediated by
phytochrome on seed germination and
flowering.
Tropism:
directional growth response of plant organs to
an environmental stimulus; results from
differential growth (usually differential cell
elongation)

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Tropisms
Gravitropism:
growth directed by the
gravitational field
Thigmotropism:
growth response to touch
Phototropism:
growth response to light

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Phototropism
• Phototropism:
growth toward (or away from)
light
Light is perceived by blue light
photoreceptors (phototropins)

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Introduction
•Whatisaplanthormone?
Planthormonecanbedefinedasasmallorganic
moleculethatelicitsaphysiologicalresponseatvery
lowconcentrations.
1.Synthesizedbyplantsandbroadlydistributed
withintheplantkingdom.
2.Showspecificbiologicalactivityatverylow
concentrations.
3.Displaymultiplefunctionsinplants.

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Plant Hormones
•Planthormonesclassification:
•Thefiveclassicalhormones:
1.Auxin
2.Cytokinin
3.Gibberellin
4.Abscisic acid
5.Ethylene
Additional substances considered as plant Hormones:
1.Polyamines
2.Jasmonates
3.Salicylic acid
4.Brassinosteroids
5.Signal peptides

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Major functions of auxin
1-Promotes elongation growth in shoots
(phototropism)
2-Inhibits elongation growth in roots
(gravitropism)
3-Promotes lateral bud dormancy
(“apical dominance”)
4-Controls (with cytokinins)
organogenesis in tissue culture

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Actions of Auxin: Phototropism and Gravitropism
Phototropism is mediated by the lateral
redistribution of auxin.

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Developmental effects of Auxin
–Auxin regulates apical dominance.

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Developmental effects of Auxin
–Auxin delays the onset of leaf abscission.
–Auxin transported from the blade normally prevents abscission.
–Abscission is triggered during leaf senescence, when auxin is no longer being
produced.

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Developmental effects of Auxin
–Auxin promotes fruit development.

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Developmental effects of Auxin
–Auxinpromotestheformationoflateral
andadventitiousroots.

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Figure39:Effectof6.0mg/lTDZtreatmentoninvitro
multiplication,shootlengthandnumberofleaves/explantofcoffee
(CoffeaarabicaL.)(Oudaynicultivar).
(Odayni.cultivar).

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Cytokinins
Oppose apical dominance –
promote outgrowth of lateral buds
Regulate organogenesis in tissue culture
Stimulate cell division in young shoots and leaves
Delay leaf senescence

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Cell Division and Plant Development
–Crowngallisdramaticnaturalevidenceofthemitoticpotentialof
matureplantcells.

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Biosynthesis, Metabolism and Transport of Cytokinins
–Crown gall cells have acquired a gene for cytokinin synthesis

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The Biological Roles of Cytokinins
–The auxin: cytokinin ratio regulates morphogenesis in cultured
tissues.

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The Biological Roles of Cytokinins
–The auxin: cytokinin ratio regulates morphogenesis in cultured
tissues.
IBA IBA+Zeatin

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The Biological Roles of Cytokinins
–Cytokinins promote chloroplast development.
Dark Dark + Cytokinin

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Figure39:Effectof6.0mg/lTDZtreatmentoninvitro
multiplication,shootlengthandnumberofleaves/explantofcoffee
(CoffeaarabicaL.)(Oudaynicultivar).
(Odayni.cultivar).

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Figure34:Effectof8.0mg/lBAtreatmentoninvitromultiplication,
shootlengthandnumberofleaves/explantofcoffee(Coffeaarabica
L.)(Dawaeirycultivar).

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Effects of Ethylene
–Leaf epinasty results when ACC from the root is transported to
the shoot.
Fruit ripening
+ Ethylene

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Developmental and Physiological Effects of ABA
–ABA closes stomata in response to water stress.

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–GA biosynthesis occurs in developing seeds.
Biosynthesis and Catabolism of Gibberellins

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–GAsareknowntoberegulatorsofmanyphasesofhigherplant
development,includingseedgermination,stemgrowth,induction
offlowering,pollendevelopmentandfruitgrowth.
Gibberellins: Their Discovery and Chemistry

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–From the time of their discovery, GAs were known to be effective in promoting
stem elongation.
–Onlyfewofthe136knownGAshaveintrinsicbiologicalactivity.Theseinclude
GA
1,GA
3,GA
4,GA
5,GA
6andGA
7.
Gibberellins: Their Discovery and Chemistry

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–GAs can stimulate stem growth in genetically dwarf mutants by
promoting internode elongation.
Effects of Gibberellins on Growth and Development

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–GA induces the synthesis of α-amylase in aleurone layer.
–Cereal grains can be divided into three parts: the embryo, the endosperm and
the testa-pericarp. The endosperm is surrounded by aleurone layer.
Gibberellin Responses

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