Transcript PLANT HORMONE

PLANT HORMONE
PLANTS UBER ALLES
(Plants as control freaks)
OUTLINE
• History and Scientists involved
• Control Systems in plants and animals
• Differences between plant and animal
hormones
• Hormone action
• Plant Hormone and effects
• Experimental Evidence
Scientists and History of Plant
Hormones
• Charles and Francis Darwin – initial proposition1880
• Boysen- Jensen – 1910
• Went-1930
• Skoog-1950
• Kurosawa-1920
• Addicott-US,Wareing-England
• Various fruit growers – 1960’s
• Australian Scientists - 2005 +
CONTROL SYSTEMS
• Necessary for response to stimuli
• Nervous system in animals
• Tropic response systems in plants and some
invertebrates
• Hormonal systems in both plants and animals
• Endocrine
• Exocrine
• Hormonal mimics
Differences between Plant and animal
Hormones
• Animal hormones produced by specific glands
and/or cells.
• Plant hormones are produced by specific
regions – ie. Meristems, cambriums ets.
• Most animal hormones are transported in
some way via blood or by ducts
• Plant hormones generally must diffuse into
adjacent cells or are carried by phloem
Hormonal Action
• Most hormones act by
way of the second
messenger theory. This
states that the hormone
binds with a receptor in
the cell membrane
which then triggers an
induction of chemical
reactions causing
specific protein to form
HORMONAL ACTION
• Once induction has occurred, this frequently
sets up a cascade effect which triggers other
responses. Ie. Giberillins initiate water uptake
in seeds which then causes a multitude of
other responses such as production of
amylase
• These effects are slow to act but long lasting
in permanent changes.
Plant Hormones
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Auxins
Cytokinins
Giberillins
Abscissic Acid
Ethylene
Florigen
Artificial mimics
Strigolactones
Auxins
• Growth of apical meristem and
supression of lateral meristem
• Cellular eleongation in grass
and herbs
• Differentiation of Vascular
Tissue
• Fruit Development and
parthenocarpy
• Wound repair and
development of adventitious
roots
• Calcium release – promotes
activation of calmodulin –
control of calcium receptors
Cytokinins
• Stimulate cell division
• Organogenesis in
connection with auxins
• High cytokinin/auxin rations
favor stem and leaf
development
• Low rations favor root
development
• Senescence and
programmed death of cells
–longer shelf life of
vegetable in grocery stores
Giberillins
• Rapid , Extensive
growth of intact plants
• Seed germination and
removal of inhibitions
• Juvenile characteristics
• Increase of fruit size in
seedless varieties
• Foolish seedling disease
Ethylene
• Fruit Ripening –one
rotten apple spoils the
bushel
• Flowering inhibited in
most plants – exception
Bromeliads
• Sex expression in diecious
plants – holly
• Abscission – initiates
break down of middle
lamella at leaf /stem
juncture
Abscissic Acid
• Closes stoma in drought
conditions
• Creates dormancy in
seeds and buds
• Formation of abscissic
layer in leaves causing
death and drop of leaf
• Counteracts stimulatory
effects of other
hormones
Florigen
• Stimulates flowering
• Has been proven to
exist but has never
been isolated
• Experiments with long
day and short day
plants
Strigolactones
• Stimulates mycorrhizial
fungal attachment to
roots
• Stimulates formation of
lateral buds(Fibionacci
numbers)
• Helps seeds break
dormancy after fire
(Australian Fire Ecology)