Transcript Chapter 1 Notes

Chapter 39 Notes
Plant Responses to
Internal and External
Signals
Concept 39.1
Concept 39.1
Concept 39.1
Messages are sent by hormones through
a signal-transduction pathway
- a hormone binds to a specific receptor
on the cell wall
- the binding stimulates the production
of a secondary messenger
- the secondary messenger trigger's the
cell’s response to the original signal
Concept 39.1
Concept 39.1
Concept 39.2
Hormones: chemical signals that
coordinate the parts of an organism
- compound that is produced by one
part of the body and is transported to
other parts to bind to receptors in order
to trigger responses
Concept 39.2
Tropism: any growth response that
results in curvatures of whole plant
organs toward or away from stimuli
Phototropism: the growth of a shoot
toward light
- directs growing seedlings so
photosynthesis can occur
Concept 39.2
- the tip of the seeding is enclosed in a
sheath called the coleoptile; if the tip is
removed, the coleoptile would not curve
- a signal is transmitted downward from
the tip of the elongating region of the
coleoptile
Concept 39.2
Concept 39.2
Plant hormones help coordinate growth,
development, and responses to
environmental stimuli
- response to a hormone depends on its
relative concentration compared with
other hormones
- hormonal balance controls growth and
development
Concept 39.2
Auxin
- any chemical substance that promotes
the elongation of coleoptiles
- moves from the shoot tip down to the
base of the plant
- if concentrations are too high, auxin
will inhibit growth
Concept 39.2
- auxin stimulates proton pumps which
in turn increases voltage across the
membrane and lowers the pH in the cell
wall
- the acidification activates enzymes
called expansins which help allow the
cell to grow
Concept 39.2
Concept 39.2
Cytokinins
- stimulate cytokinesis, or cell division
- produced in actively growing tissues;
are needed to be present along with
auxin for cells to divide
Concept 39.2
Cytokinins and auxin control apical
dominance, the ability of the terminal
bud to suppress the development of
axillary buds
- if the terminal bud is removed, the
inhibition of axillary buds is removed
and the plant becomes bushier
Concept 39.2
Concept 39.2
Gibberellins
- stimulate growth in the stems and
leaves, but not in the roots
- stimulates cell elongation and division
- the effects of gibberellins are seen
when they are given to a plant that is
dwarfed
Concept 39.2
Concept 39.2
Abscisic Acid
- slows down growth
- seed dormancy: high levels of ABA
inhibit germination; only when the ABA
is inactivated will the seed germinate
- drought stress: when a plant begins to
wilt, ABA causes stomata to close
Concept 39.2
Ethylene
- produced by plants in response to
environmental stresses
- also occurs in fruit ripening and
programmed cell death
- triple response that allows plants to
circumvent an obstacle
Concept 39.2
Concept 39.2