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HORMONE PHYSIOLOGY AND
SIGNAL TRANSDUCTION
Huseyin Tombuloglu, Phd.
GBE 304 Spring 2015
ABSCISIC ACID
A Seed Maturation
and Antistress Signal
Brassicas in the field
Poppies in the field
Controlling of timing
How they know the blooming time?
Figure 23.3 Precocious germination in the ABAdeficient vivipary 14 mutant of maize
Abscisic Acid (ABA)
For many years, plant physiologists suspected
that the phenomena of seed and bud
dormancy were caused by inhibitory
compounds, and they attempted to extract
and isolate such compounds from a variety of
plant tissues, especially dormant buds.
Abscisic Acid (ABA)
Natural inhibitory compound.
Affects bud and seed dormancy.
Affects leaf abscission.
Controls stomatal closure in drought-stressed
plants.
Promotion of flowering in short-day
plants….plants that flower when the daylength is shorter than some critical period.
May also influence cold-hardiness.
Functions of ABA
Additions if ABA, or natural production in
plants will:
Promote seed dormancy.
Promote bud dormancy.
Accelerate leaf abscission.
The dormancy response caused by ABA in
plants may result from suppression of RNA
and protein synthesis.
http://www.nature.com/nat
ure/journal/v410/n6826/fu
ll/410327a0.html
Positive ABA-activated regulators (top, in green) and negative ABAsignalling regulators (bottom, in red) in guard cells are shown.
http://biology.ucsd.edu/l
abs/schroeder/clickable
gc.html
Two more hormones…
There are two more hormones to discuss...
Brassinolide (Br)
It is a sterol, much like estrogen and
testosterone (which function as sex
hormones in animals).
Critical for normal plant growth and
development.
Plays roles in stem elongation, leaf
development, pollen tube growth, vascular
differentiation, seed germination,
photomorphogenesis, and stress responses.
Jasmonic Acid (JA)
JA is a fatty-acid-derived plant hormone that
is similar in overall structure to
physiologically active small molecules from
animals called prostaglandins.
In plants, jasmonic acid is firmly associated
with pathogen defense pathways.
Jasmonic Acid (JA)
The physical stimuli of certain insects can
trigger the synthesis of JA, which then
functions to increase expression of genes
involved in defending the plant.
Microbial and viral pathogens can also trigger
JA synthesis.
The study of JA-mediated events in the plant
cell are of interest to plant pathologists who
wish to engineer transgenic plants that are
disease-resistant.
Signal Transduction
 Signals from outside a cell can be perceived,
sometimes by receptors that span the plasma
membrane.
 After stimulation of such receptors, information can
be relayed by a series of small molecules or proteins
to the cell nucleus, where activation of specific
transcription factors can stimulate new gene
expression programs.
 The resulting gene expression results in the
production of new proteins that can function in the
final biological responses to the signal.
Signal Transduction
Summary
Hormones elicit a multitude of growth &
development responses in plants.
Identified the major plant hormones.
Identified modes of action/practical
applications.
Identified signal transduction mechanisms.
Play vital roles in sensing
endogenous/exogenous signals…and causing
a plant response.