Transcript Plant Structure and Function - Cal State LA

BIOL 100C:
Introductory Biology III
Secondary Growth in Plants /
Leaf Structure & Adaptations
Dr. P. Narguizian
Fall 2012
Principles of Biology
Plant Growth and Development
Leaf structure and function.
The ground tissue in the leaf makes two layers: the
palisade mesophyll with long columnar cells just
under the upper epidermis, and the spongy mesophyll
with more rounded cells below, where photosynthesis
occurs.
Principles of Biology
Plant Growth and Development
Figure 7 Cross-sectional anatomy of a leaf.
Leaves are composed of four general
tissue layers. The upper epidermis
cells make up the outermost layer of
the top of the leaf. These cells generate
a waxy waterproofing layer called the
cuticle.
The palisade mesophyll is a densely
packed collection of photosynthetic
cells. The spongy mesophyll is a
loosely packed collection of
photosynthetic cells. The air spaces of
the spongy mesophyll create a large
surface area for the photosynthetic cells
to exchange gases (input of CO2 and
output of O2).
The lower epidermis contains the
stomata through which gases enter and
leave the air spaces of the spongy
mesophyll.
Principles of Biology
Plant Growth and Development
Secondary growth is widening or
thickening growth.
•Lateral or thickening growth relies on particular lateral
meristems: the vascular cambium and the cork cambium.
•Cork cambium produces a tougher epidermal tissue
called the periderm.
•All of these additional layers bulk up the plant, providing
strength and additional energy reserves.
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Plant Growth and Development
Figure 8 Secondary and primary growth.
Secondary growth and its
interaction with primary growth.
New stems and leaves emerge
from the apical meristem, exhibiting
primary growth. Concurrently, the
stem formed during the former
year's growth thickens by lateral
growth.
The vascular cambium produces
cells inward that form secondary
xylem; it also produces new cells
outward to form secondary phloem.
The outward growth pushes
through the epidermis and cortex of
last year's primary growth. The
parenchyma cells of the cortex
become the cork cambium, which
produces cork cells of the periderm.
Principles of Biology
Plant Growth and Development
Bark is in part a manifestation of secondary
growth.
•Bark consists of periderm and all the other tissues
exterior to the vascular cambium including the
secondary phloem.
•Removing bark in a complete ring around a tree
would kill the tree because the vascular cambium
and secondary phloem would be removed.
•Without these, nutrients cannot sustain living roots.
Principles of Biology
Plant Growth and Development
Figure 10 Layers of a tree trunk.
A cross-section through
a woody stem. Notice
how the bark integrates
with the vascular
network of the tree,
making it inseparable
from the functioning
plant.
Principles of Biology
Plant Growth and Development
Figure 11 Tree rings.
Annual rings are visible on
this cross-section of a
Ponderosa pine (Pinus
ponderosa Pinaceae).
The growth rings can be
used to provide
dendrochronologists
information regarding past
environmental conditions
(e.g. drought, pollution,
and even fire).
Principles of Biology
Plant Growth and Development
Plant Morphogenesis and
Differentiation
Morphogenesis: the establishment of
form and function.
Principles of Biology
Plant Growth and Development
What cellular directives drive the development and
growth of these primary and secondary tissues?
•Asymmetrical cell division causes polarity: one end of
an organism has a different structure and chemistry
from the other end.
•The first step in morphogenesis.
Principles of Biology
Plant Growth and Development
Figure 12 Asymmetrical cell division.
The mechanism of
asymmetrical division gives rise
to differentiation in plant cells.
A meristemoid cell divides
asymmetrically into a smaller
guard mother cell. The guard
mother cell then divides
symmetrically to form a second
guard cell of equal size.
Principles of Biology
Plant Growth and Development
What determines pattern formation and
development of form in the plant?
• If one transplants a mature root or leaf cell in tissue culture, the
cells dedifferentiate to meristematic cells. Thus, every cell in a
plant has the same genetic blueprint and potential to be any
other kind of cell.
• Pattern formation, or the development of form of a plant,
depends on the expression of genes in each cell according to
its position in the plant and what is happening in nearby cells.
Principles of Biology
Plant Growth and Development
Figure 13 Gene control by neighboring cell types.
Plant cells affect each
other, working as a system
to regulate growth and
development of
specialized cells in
balance with plant needs.
Principles of Biology
Plant Growth and Development
Plants go through several developmental
stages.
• Humans age with hormonal and physical changes affecting our
entire body.
• Plants also go through phase changes, but only the daughter
cells of the shoot apical meristem change in structure and
function.
• Leaf shape and position often change from juvenile phase to
adult
Principles of Biology
Plant Growth and Development
Figure 14 Changes in Eucalyptus leaf morphology.
As the leaves of this
Eucalyptus globulus
plant age, they change
shape. Juvenile stage
is in upper left, and
adult stage is in lower
right.
Principles of Biology
Plant Growth and Development
Figure 15 Plant model organism.
Arabidopsis thaliana, a model
organism for plant development
research, is shown here. The
upper image depicts a
multileaved plant, with a small
cluster of flowers.
The bottom image is a close up
of A. thaliana flowers, the
characteristic four petals and
sepals, and six stamens of the
Brassicaceae (Mustard Family).
Principles of Biology
Plant Structure and Function
Figure 1 Aquatic plant leaves.
Land plant adaptations
evolved as a result of
variations of water
availability on land.
• Shoots growing out of
shallow water
produce a waxy,
waterproof surface,
reducing water loss.
This aquatic lily has broad flat waxy leaves that
rest on the surface of water, maximizing exposure
to sunlight.
Principles of Biology
Plant Structure and Function
Figure 2 Conifer leaves.
Land plant
adaptations evolved
as a result of
variations of water
availability on land.
• In general, plants in arid
and cold climates grow
smaller leaves, whereas
plants in warm, moist
climates display leaves
with larger surface areas.
Principles of Biology
These needle-shaped conifer leaves maximize
photosynthesis with minimal water loss, due to
both their shape (which minimizes surface
area/volume), as well as their waxy coating.
Plant Structure and Function
Figure 3 Tropical leaves.
Trees in tropical forests have access to abundant
water and therefore can have large leaves without
risking dehydration.
Principles of Biology
Plant Structure and Function
Figure 4 Leaf area index.
Leaf arrangement
patterns maximize
accessibility to light for
photosynthesis.
• The leaf area index
measures the average
degree of coverage by
leaves, because leaves
are not static structures.
The leaf area index equals the ratio of the
total upper leaf surface of a plant divided by
the surface area of the ground covered (as
viewed from above) by the plant.
Principles of Biology
Plant Structure and Function
Leaf arrangement patterns maximize
accessibility to light for photosynthesis.
• In each species of plant, arrangement of leaves on the stem, called phyllotaxy,
occurs in a fixed pattern.
Leaf orientation affects how a plant captures light.
• The way a leaf orients toward the sun also has an effect on the amount of light captured.
• Because horizontal leaves capture sunlight more efficiently, growth can occur in low-light
areas such as in the shade.
• In brightly lit habitats, most vertical leaves such as seen on grasses provide efficient
orientation.
Principles of Biology
Plant Structure and Function
Figure 6 Climbing ivy.
This ivy plant climbs on
the bark of a tree,
allowing it to access
more sunlight.
Principles of Biology
Plant Structure and Function
Figure 7 Roots.
Roots are an important
adaptation to plants living
on land. Deep roots are
adaptations in plants that
need to reach for water
below parched soil.
Principles of Biology
Plant Structure and Function
Plant Adaptations Below Ground
•Along with the sugar and gases leaves and stems
provide, plants require water and minerals
absorbed from soil via their roots.
•Roots also act as a foundation, preventing
collapse and easy breakage.
Principles of Biology
Plant Structure and Function
Figure 8 Fibrous roots.
Most monocots, like these
grasses, do not grow tall
and have fibrous root
systems to maximize
uptake of water and
nutrients near the surface
of the soil.
Principles of Biology
Plant Structure and Function
Exceptions to the rule.
• Although the entire root system helps anchor the plant, most of the
uptake of water and minerals occurs at the growing tips and associated
root hairs.
• Plants require nitrogen in relatively large amounts to construct
proteins, nucleic acids, and chlorophyll.
• One way in which plants acquire nitrogen is through a symbiotic
relationship with the bacteria in the genus Rhizobium.
• In mycorrhizae, fungal hyphae, or filaments, grow into the roots.
• Hyphae create a significantly broader surface area for water and
nutrient absorption than a root system that develops alone.
• In return, the fungi take nutrients from the organic molecules produced
from photosynthesis.
Principles of Biology
Plant Structure and Function
Figure 9 Symbiotic relationships between microorganisms and plant roots.
Two types of symbiotic
relationships:
a) A nitrogen-fixing bacterium
(Rhizobium) in the root
cortical cell of a leguminous
plant.
b) b) More common are
mycorrhizae; fungal and root
symbiosis.
Principles of Biology
Plant Structure and Function
The Dynamic Symplast
• When plants grow on land, the water and nutrients absorbed by the
roots must be transported to the photosynthetic cells.
• Phloem, a specialized plant tissue, transports sugars and other
solutes such as mineral nutrients, amino acids, and hormones within a
plant.
• Xylem, in contrast, transports water and dissolved nutrients.
• Transport in plants takes place through both living and nonliving cells.
The combined cytosol of all living cells in a plant is called the
symplast.
• The symplast also includes the cytoplasm of plasmodesmata,
cytoplasmic channels that connect adjacent living cells.
Principles of Biology
Plant Structure and Function
Figure 10 Plasmodesmata.
The Dynamic Symplast
• Allow water and nutrients to reach cells
seamlessly, enabling plants to address
water shortages in a timely fashion.
Plasmodesmata channels form
between adjacent plant cells.
Principles of Biology