Plant Development
Chapter 31 Part 1
Impacts, Issues
Foolish Seedlings, Gorgeous Grapes
 Gibberellin and other plant hormones control the
growth and development of plants –
environmental cues influence hormone secretion
31.1 Patterns of Development in Plants
 Germination
• Process by which a dormant mature embryo
sporophyte in a seed resumes growth
• Certain species-specific conditions may be
required to break dormancy
• Begins when water activates enzymes in the seed
• Ends when the embryo breaks the seed coat
Patterns of Development in Plants
 Growth (increase in cell number and size)
occurs primarily at meristems
 Differentiation results in the formation of tissues
and parts in predictable patterns
 Patterns of plant development are an outcome of
gene expression and environmental influences
Anatomy of a Corn Seed
seed coat fused
with ovary wall
endosperm cells
cotyledon
coleoptile
plumule
(embryonic
shoot)
embryo
hypocotyl
radicle
(embryonic
root)
Fig. 31-2, p. 524
Early Growth of Corn (Monocot)
Fig. 31-3a, p. 525
coleoptile
branch
root
primary
root
coleoptile
hypocotyl
radicle
A After a corn grain (seed) germinates, its radicle and
coleoptile emerge. The radicle develops into the primary
root. The coleoptile grows upward and opens a channel
through the soil to the surface, where it stops growing.
Fig. 31-3a, p. 525
Fig. 31-3b, p. 525
primary leaf
coleoptile
adventitious
(prop) root
branch root
primary root
B The plumule develops into the seedling’s primary shoot, which
pushes through the coleoptile and begins photosynthesis. In corn
plants, adventitious roots that develop from the stem afford
additional support for the rapidly growing plant.
Fig. 31-3b, p. 525
coleoptile
branch
root
primary
root
coleoptile
hypocotyl
radicle
A After a corn grain (seed) germinates, its
radicle and coleoptile emerge. The radicle
develops into the primary root. The
coleoptile grows upward and opens a
channel through the soil to the surface,
where it stops growing.
primary
leaf
coleoptile
adventitious
(prop) root
branch
root
primary root
B The plumule develops into the seedling’s
primary shoot, which pushes through the
coleoptile and begins photosynthesis. In corn
plants, adventitious roots that develop from the
stem afford additional support for the rapidly
growing plant.
Stepped Art
Fig. 31-3, p. 525
Animation: Plant development
Early Growth of a Bean (Eudicot)
Fig. 31-4a, p. 525
seed
coat radicle
cotyledons (two)
hypocotyl
primary root
A After a bean seed germinates, its radicle emerges
and bends in the shape of a hook. Sunlight causes the
hypocotyl to straighten, which pulls the cotyledons up
through the soil.
Fig. 31-4a, p. 525
Fig. 31-4b, p. 525
B Photosynthetic cells in the cotyledons
make food for several days, then the
seedling’s leaves take over the task.
The cotyledons wither and fall off.
primary
leaf
primary
leaf
withered
cotyledon
branch root
primary root
root nodule
Fig. 31-4b, p. 525
Summary: Eudicot Development
germination
mature
sporophyte
(2n)
zygote
in seed (2n)
fertilization
meiosis
in anther
DIPLOID
meiosis
in ovary
HAPLOID
eggs (n)
sperm (n)
microspores
(n)
megaspores
(n)
male
gametophyte (n)
female
gametophyte (n)
Fig. 31-22, p. 535
31.1 Key Concepts
Patterns of Plant Development
 Plant development includes seed germination
and all events of the life cycle, such as root and
shoot development, flowering, fruit formation,
and dormancy
 These activities have a genetic basis, but are
also influenced by environmental factors
31.2 Plant Hormones
and Other Signaling Molecules
 Plant development depends on cell-to-cell
communication – mediated by plant hormones
 Plant hormones
• Signaling molecules that can stimulate or inhibit
plant development, including growth
• Five types: Gibberellins, auxins, abscisic acid,
cytokinins, and ethylene
Gibberellins
 Gibberellins induce
cell division and
elongation in stem
tissue, and are
involved in
germination
Auxins
 Auxins promote or inhibit cell division and
elongation, depending on the target tissue
 Auxin produced in a shoot tip prevents growth of
lateral buds (apical dominance)
 Auxins also induce fruit development in ovaries,
and lateral root formation in roots
Rooting Powder with Auxin
Abscisic Acid
 Abscisic acid (ABA) inhibits growth, is part of a
stress response that causes stomata to close,
and diverts products of photosynthesis from
leaves to seeds
Cytokinins
 Cytokinins form in roots and travel to shoots,
where they induce cell division in apical
meristems
 Cytokinins also release lateral buds from apical
dominance and inhibit leaf aging
Ethylene
 Ethylene
•
•
•
•
The only gaseous hormone
Produced by damaged or aging cells
Induces fruit and leaves to mature and drop
Used to artificially ripen fruit
Major Plant Hormones and Their Effects
Commercial Uses of Plant Hormones
Other Signaling Molecules
 Besides hormones, other signaling molecules
are involved in plant development
•
•
•
•
•
Brassinosteroids
FT protein
Salicylic acid
Systemin
Jasmonates
31.3 Examples of Plant Hormone Effects
 Gibberellins and barley seed germination
•
•
•
•
Barley seed absorbs water
Embryo releases gibberellin
Gibberellin induces transcription of amylase gene
Amylase breaks stored starches into sugars used
by embryo for aerobic respiration
Gibberellins in Barley Seed Germination
Gibberellins in Barley Seed Germination
Gibberellins in Barley Seed Germination
aleurone
endosperm
embryo
gibberellin
A Absorbed water causes cells of a barley embryo
to release gibberellin, which diffuses through the
seed into the aleurone layer of the endosperm.
Fig. 31-7a, p. 528
amylase
B Gibberellin triggers cells of the aleurone layer to
express the gene for amylase. This enzyme diffuses
into the starch-packed middle of the endosperm.
Fig. 31-7b, p. 528
sugars
C The amylase hydrolyzes starch into sugar monomers,
which diffuse into the embryo and are used in aerobic
respiration. Energy released by the reactions of aerobic
respiration fuels meristem cell divisions in the embryo.
Fig. 31-7c, p. 528
A Absorbed water causes
cells of a barley embryo to
release gibberellin, which
diffuses through the seed into
the aleurone layer of the
endosperm.
B Gibberellin triggers cells
of the aleurone layer to
express the gene for
amylase. This enzyme
diffuses into the starchpacked middle of the
endosperm.
C The amylase hydrolyzes
starch into sugar monomers,
which diffuse into the embryo
and are used in aerobic
respiration. Energy released by
the reactions of aerobic
respiration fuels meristem cell
divisions in the embryo.
aleurone
endosperm
embryo
gibberellin
amylase
sugars
Stepped Art
Fig. 31-7a, p. 528
Examples of Plant Hormone Effects
 Auxin (IAA) plays a critical role in all aspects of
plant development
•
•
•
•
•
•
First division of the zygote
Polarity and tissue pattern in the embryo
Formation of plant parts
Differentiation of vascular tissues
Formation of lateral roots
Responses to environmental stimuli
Directional Transport of Auxin
auxin
time
time
auxin
A A coleoptile stops
growing if its tip is
removed. A block of
agar will absorb auxin
from the cut tip.
B Growth of a de-tipped
coleoptile will resume
when the agar block
with absorbed auxin is
placed on top of it.
C If the agar block is
placed to one side of
the shaft, the coleoptile
will bend as it grows.
Fig. 31-8, p. 529
time
A A coleoptile stops
growing if its tip is
removed. A block of agar
will absorb auxin from the
cut tip.
B Growth of a de-tipped
coleoptile will resume
when the agar block with
absorbed auxin is placed
on top of it.
time
C If the agar block is
placed to one side of the
shaft, the coleoptile will
bend as it grows.
Stepped Art
Fig. 31-8, p. 529
Animation: Auxin’s effects
Examples of Plant Hormone Effects
 Jasmonates signal plant defenses
• Wounding by herbivores cleaves peptides (such
as systemin) in mesophyll cells
• Activated peptides stimulate jasmonate synthesis,
which turns on transcription of several genes
• Some gene products slow growth
• Other gene products signal wasps to attack
specific herbivores responsible for damage
Jasmonates in Plant Defenses
31.2-31.3 Key Concepts
Mechanisms of Hormone Action
 Cell-to-cell communication is essential to
development and survival of all multicelled
organisms
 In plants, such communication occurs by
hormones