Transcript FUNCTIONS OF AUXINS Stimulates cell elongation Stimulates

• Plants lack nerves and therefore only
possess chemical coordination.
• Plants show movements of two types:
• Movement of locomotion and movement of
curvature.
• The latter is more prominent in plants.
Movement of locomotion- changes in
position of the whole organism or cellular
components.
• They are of two types:
a) Autonomic or spontaneous movements
of locomotion- They occur automatically
due to intrinsic reasons. For eg. Flagellar
movements in unicellular algae like
Chlamydomonas.
Taxis
• Small algae such as Euglena and
Chlamydomonas can exhibit movements
of the whole organism and such
movements are called taxis
b) Paratonic or Tactic movements of
Locomotion- They are locomotory
movements of complete cells or cell
organelles in response to external stimuli.
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Chemotaxis- Locomotory movement in
response to chemicals.
Phototaxis- Locomotory movements in
response to light.
Movements of curvature- Movements of
plants parts in relation to others.
• They are of two types:
a) Turgor movements- They occur in plant organs which have
regions of bending where cells shrink or swell up due to
loss or gain of turgidity. These movements are reversible.
b) Growth movements- unequal or differential growth in
different parts of an organ results in its bending. They
are autonomic or paratonic.
Trophic Movements
Trophic Movements are
further classified into the
following• Phototropism – Direction
growth movement of
curvature in response to
light. Shoot apices are
positively phototropic
while the root apices are
negatively phototropic.
The light effective for
phototropic response is
blue light.
Trophic Movements
• Geotropism-–
Direction growth
movement of
curvature in response
to gravity. Shoot
apices are negatively
geotropic while the
root apices are
positively geotropic
Trophic Movements
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Hydrotropism- Directional growth movement of
curvature which occurs in response to unilateral
stimulus by water. Hydrotropism is generally shown by
roots, which are positively geotropic.
Activity for testing hydrotropism:
Place some germinated seeds in moist saw dust
contained in a sieve. The radicles will move down the
pores of the seed in response to gravity. However after
some time they will curve and re-enter back into the
saw dust showing a response towards water, which is
greater than gravity.
Trophic Movements
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Thigmotropism- Directional growth
movements of curvature which occurs in
response stimulus of contact. In twiners
and tendrils – which respond by turning
around a support.
Chemotropism- Directional movement of
growth in response to a chemical
stimulus.
Trophic Movements
• Activity for testing Chemotropism:
Take some seeds and germinate them in
minimal medium. A drop of nutrient
medium containing boron will result in
bending of pollen tubes towards it from all
directions.
Nasties
• Another type of plant
movement is called
nastic movement
(plural nasties) –
direction of response
independent of
direction of stimulus.
Plant Hormones
FUNCTIONS OF AUXINS
Stimulates cell elongation
Stimulates cell division in the
cambium and, in combination
with cytokinins in tissue culture
Stimulates differentiation of
phloem and xylem
Stimulates root initiation on stem
cuttings and lateral root
development in tissue culture
Mediates bending in response to
gravity and light
Delays leaf senescence
The auxin supply from the apical bud
suppresses growth of lateral buds
The auxin supply from the apical bud
suppresses growth of lateral buds
Can inhibit or promote leaf and fruit
abscission
FUNCTIONS OF GIBBERELINS
• Stimulate stem elongation by stimulating cell division and
elongation.
• Stimulates flowering in response to long days.
• Breaks seed dormancy in some plants.
FUNCTIONS OF CYTOKININS
• Stimulates cell division.
• Stimulates the growth of lateral buds-release of apical
dominance.
• Stimulates leaf expansion resulting from cell
enlargement.
• May enhance stomatal opening in some species.
FUNCTIONS OF ABSCISIC ACID
• Stimulates the closure of stomata (water stress
brings about an increase in ABA synthesis).
• Inhibits shoot growth
• Induces seeds to synthesize storage proteins.
• Has some effect on induction and maintanance
of dormancy.
FUNCTIONS OF ETHYLENE
• Stimulates the release of dormancy.
• Stimulates shoot and root growth and
differentiation (triple response)
• Stimulates leaf and fruit abscission.
• Stimulates flower opening.
• Stimulates flower and leaf senescence.
• Stimulates fruit ripening