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 stControl-and-coordination

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Control and coordination in plants
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• 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.

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• Movement of locomotion- changes in position of
  the whole organism or cellular components.
• They are of two types

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• a) Autonomic or spontaneous movements of
  locomotion- They occur automatically due to
  intrinsic reasons. For eg. Flagellar movements in
  unicellular algae like Chlamydomonas.

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Taxis

• Small algae such as Euglena and Chlamydomonas can
  exhibit movements of the whole organism and such
  movements are called taxis

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• b) Paratonic or Tactic movements of Locomotion-
  They are locomotory movements of complete cells
  or cell organelles in response to external
  stimuli.
• Chemotaxis- Locomotory movement in response to
  chemicals.
• Phototaxis- Locomotory movements in response to
  light.

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• Movements of curvature- Movements of plants
  parts in relation to others.
• They are of two types

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• 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.

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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.

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Trophic Movements

• Geotropism- Direction growth movement of
  curvature in response to gravity. Shoot apices
  are negatively geotropic while the root apices
  are positively geotropic

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Trophic Movements

• 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.

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Trophic Movements

• 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.

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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.

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Nasties

• Another type of plant movement is called nastic
  movement (plural nasties)
• direction of response independent of
  direction of stimulus.

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Plant Hormones
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FUNCTIONS OF AUXINSStimulates cell
elongation Stimulates cell division in the
cambium and, in combination with cytokinins in
tissue culture Stimulates differentiation of
phloem and xylem
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Stimulates root initiation on stem
cuttings and lateral root development in tissue
culture Mediates bending in response to
gravity and light Delays leaf senescence
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The auxin supply from the apical bud
suppresses growth of lateral budsThe auxin
supply from the apical bud suppresses growth of
lateral buds Can inhibit or promote leaf and
fruit abscission
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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.

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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.

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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.

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FUNCTIONS OF ETHYLENE

• Stimulates the release of dormancy.
• Stimulates shoot and root growth and
  differentiation (triple response)
• Stimulates leaf and fruit abscission.

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• Stimulates flower opening.
• Stimulates flower and leaf senescence.
• Stimulates fruit ripening