Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Monocot or Dicot?

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

Monocot or Dicot?


Monocot or Dicot?


Monocot or Dicot


Monocot or Dicot?


Monocot or Dicot?


Monocot or Dicot?


Monocot or Dicot?


Monocot or Dicot?

Monocot Dicot


Monocot or Dicot?

DICOT MONOCOT


Monocot or Dicot

DICOT MONOCOT


Monocot or Dicot?

Dicot


Monocot or Dicot?

Dicot


Monocot or Dicot?

Dicot


Monocot or Dicot?

Monocot


PowerPoint Lectures for Biology, Seventh Edition

Neil Campbell and Jane Reece

Lectures by Chris Romero

Chapter 39Chapter 39

Plant Responses to Internal and External Signals


Concept 39.2: Plant hormones help coordinate growth, development, and responses to stimuli

• Hormones are chemical signals that coordinate different parts of an organism


The Discovery of Plant Hormones

• Any response resulting in curvature of organs toward or away from a stimulus is called a tropism

• Tropisms are often caused by hormones


A Survey of Plant Hormones

• In general, hormones control plant growth and development by affecting the division, elongation, and differentiation of cells

• Plant hormones are produced in very low concentration, but a minute amount can greatly affect growth and development of a plant organ



Auxin—Made in the shoot tips sent to the roots.

• Stimulate cell elongation in the meristems.

• Auxin stimulates growth in the apical meristems but inhibits growth in the lateral (axillary).

– Remember primary and secondary tumors…

• This is called apical dominance—but when you snip the apical meristems off a plant the lateral buds begin to grow—the auxin is no longer inhibiting the growth of the lateral meristems.


LE 39-9

Intact plant Plant with apical bud removed

Lateral branches

“Stump” afterremoval ofapical bud

Axillary buds



Cytokinins—made in root tips sent to shoots.

• Produced in the growing roots and in developing fruits and seeds.

• Stimulate cell division and interact with auxins to control the growth of the new organ in injured plants and to balance root and shoot growth.



Gibberellins

• Gibberellins have a variety of effects, such as stem elongation, fruit growth, and seed germination


Stem Elongation

• Gibberellins stimulate growth of leaves and stems

• In stems, they stimulate cell elongation and cell division


Fruit Growth

• In many plants, both auxin and gibberellins must be present for fruit to set

• Gibberellins are used in spraying of Thompson seedless grapes





Abscisic Acid

• Two of the many effects of abscisic acid (ABA):

– Seed dormancy

• Inhibits growth once embryo is fully developed and awaiting environmental cues for completion.

– Drought tolerance (stop growing until resources available)


Drought Tolerance

• ABA is the primary internal signal that enables plants to withstand drought


Ethylene

• Plants produce ethylene in response to stresses such as drought, flooding, mechanical pressure, injury, and infection


The Triple Response to Mechanical Stress

• Ethylene induces the triple response, which allows a growing shoot to avoid obstacles

• The triple response consists of a slowing of stem elongation, a thickening of the stem, and horizontal growth


Apoptosis: Programmed Cell Death

• A burst of ethylene is associated with apoptosis, the programmed destruction of cells, organs, or whole plants


Leaf Abscission

• Ethylene plays a role in causing plants to seal off the base of the structure and drop organs that are no longer needed.

– Example—petals dropping after flowers have been pollinated

– Leaves dropping in autumn

– Fruit dropping after they’ve ripen



Fruit Ripening

• A burst of ethylene production in a fruit triggers the ripening process


TROPISM IN PLANTS

• Growth in response to light, gravity and touch.

– Phototropism

• Growing toward light

– Gravitropism

• Stems grow against gravity, roots with gravity

– Thigmotropism

• Detect and wrap around objects using tendrils

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Monocot or Dicot?

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