Download Plant Physiology - Miami-Dade Extension

Plant Physiology:
How plants work
By Adrian Hunsberger
University of Florida/IFAS
Miami-Dade County Extension
What is a Plant?
 Any of various photosynthetic, eukaryotic,
multicellular organisms of the kingdom Plantae.



Photosynthetic - the biological process where light
energy is converted to chemical energy in the form
of a sugar molecule.
Eukaryotic - an organism having a nucleus
Multicellular - an organism having more than one
cell
What Makes a Plant?
 Leaves
 Flowers
 Roots
 Seeds
 Stems
 Cellulose Cell
Walls
Plants - Two Classes
 Gymnosperms
 Do not bear fruits, but instead
have “naked seeds” in cones.
 All woody, perennial, usually
evergreen. Ex.: Conifers &
cycads
 Angiosperms
 Have flowers, have seeds which
are always in a fruit.
Plant Types
 Annual
 Short-lived plant. The entire life
cycle is completed in one growing
season.
 Biennial
 Two seasons to complete life cycle
 Perennial
 Lives from year to year, either
woody or herbaceous.
Year 1
Year 2
Plant Growth
 Plants manufacture their own food (by converting
energy from sunlight).
 All living things require energy, not just for
growth and reproduction, but also for the
maintenance of life.
 To produce food the plant requires energy,
carbon dioxide, water, and the essential nutrients.
How A Plant Grows
 Photosynthesis - “to put together with light”:
light
6CO2 + 6H2O -----------> C6H12O6 + 6O2

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Sugars can be transported
Starches can be stored
 Respiration:
C6H12O6 + 6O2 ---> 6CO2 + 6H2O + Heat
More energy stuff
 Respiration

Breaking the carbohydrates into a form
of energy the plant can use
Although we think of
respiration in animals as
breathing, breathing is
really the gas exchange
that supports respiration.
Plant Growth
 Photosynthesis
 Produces food
 Energy is Stored
 Occurs in Cells with
Chloroplasts
 Oxygen is released
 CO2 is used
 Occurs in light
 Respiration
 Uses food for Energy
 Energy is released
 Occurs in all cells
 Oxygen is used
 Water is produced
 CO2 is produced
 Occurs in Dark or
Light
Photosynthesis
 Occurs only in
chloroplasts
 Chloroplasts contain
chlorophyll where
photosynthesis occurs
 Chlorophyll, a plant
pigment, appears green
Where photosynthesis
takes place
Photosynthetic Pathway
What’s all this used for, anyway?
 Plant growth and development
 Cell division
 Cell elongation
 Where does growth occur in plants?
 Meristems
Root tip
Light
• Color
– Why don’t plants grow well in
green light?
- what about violet-blue and red
light?
Light
• Intensity
– Shade plants and full sun plants
• Duration
– Total amount in a day
– Photoperiod and flowering
Short-day – poinsettia
Day-neutral – tomato
Long-day - dill
Plant Types - Angiosperms
Have flowers, have seeds which are
always in a fruit
 Monocots – grasses, palms,
bamboo, lilies, orchids, amaryllis
 Dicots –
“broadleaves”
How substances move within the plant
Phloem – tubes that conduct food and hormones
produced by the plant from leaves to entire plant
Xylem – tubes that conduct water and minerals from
roots to entire plant
These tissues are formed by the vascular cambium
Woody dicots
Herbaceous dicots
Monocots
Growth - Monocots
 Cotyledon (seed leaves) = 1
 Shoot Elongation
 Shoots elongate from 1 growing point,
pushing material upward.
 Leaf Growth
 Occurs from a meristem,
a bud, a growing point.
Growth - Monocots
 Stem/root Diameter
Growth

Stem diameter is
determined within
the growing point no cambium layer
exists.
Growth - Dicots
 Cotyledon (seed leaves) = 2
 Shoot Elongation
 Shoots elongate or grow
in height at the tips of the
branches.
 Leaf Growth
 Occurs from meristem
(region making new cells), a bud.
Growth - Dicots (Woody)
 Stem/root Diameter Growth
 Between the wood and bark is a
thin layer of dividing cells, the
vascular cambium.
Growth - Dicots (Herbaceous)
Plant Types
 Woody- stem tissue is
tough and strong

(monocots) Stems and
roots lengthen each year.

(dicots) Stems and roots
increase in diameter
(thicken) and length each
year.
 Herbaceous
 Aerial portion of the plant
is relatively short-lived and
the tissues relatively soft.
Growth Factors – plant hormones
Very small concentrations of these substances produce
major growth changes.
 There are five groups of plant-growth-regulating
compounds:
auxin,
gibberellin (GA),
cytokinin,
ethylene, and
abscisic acid (ABA).
Growth Factors – plant hormones
Auxin causes several responses in plants:
 Bending toward a light source (phototropism)
 Downward root growth in response to gravity




(geotropism)
Promotion of apical dominance
Flower formation
Fruit set and growth
Formation of adventitious roots
Growth Factors – plant hormones
 Gibberellic acid (GA) = Gibberellins
Stimulates cell division and
elongation, breaks dormancy,
speeds germination.

 Cytokinins are found in both plants and animals.
 Stimulate cell division
 also are used to delay aging and death
(senescence).
Growth Factors – plant hormones
 Ethylene gas
 Ripening agent
 Stimulates leaf and fruit abscission.
 Ethylene is unique in that it is found only in the
gaseous form.
 Plants often increase ethylene production in
response to stress
 Car exhaust contains ethylene!
Growth Factors – plant hormones
Abscisic acid (ABA) is a general plant-growth
inhibitor.
It induces dormancy and prevents seeds from
germinating;
causes abscission of leaves, fruits, and flowers;
and
causes stomata to close.
Growth Factors - Genetic
 Plant Family
 Species
 Cultivar (“variety”)
Growth Factors - Environmental
 Water
 Air
 Light
 Pests
 Temperature
 Culture
Temperature
Heat and cold effect the rate of chemical reactions and
therefore, plant growth.
Plant Growth Factors
Plant Organs - The Root
 Roots
 Do not possess nodes, internodes
or buds.
 Function primarily in support,
water and mineral uptake
from the soil.
 Grow in both length and diameter as the plant
grows (dicots).
 Commonly grow to 2-3 times the diameter of the
shoot (canopy) area; primarily in top 12-18 inches
of soil.
Plant Organs - The Root
 Primary Root:
 generally arises from the embryo as the Radicle (seed
root). Tends to be short lived, but may turn into a tap
root in some species.
 Secondary Roots:
 Branching roots off of the
primary root, become the
permanent roots.
Types of Tree Roots
Small absorbing roots
Sinker roots
Lateral roots
Taproot (a temporary
structure)
Plant Organs - The Root
 Adventitious Roots
- arise from stem
structures.
 Root Hairs
- extensions of root
cells - these draw all
the supplies.
Factors Influencing Plant
Root Growth
Water
u Air
u Soil temperature
u Soil structure
u Soil pH
u Nutrients
u
Water

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
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Plants are 90% water, most of which is absorbed
through the roots
Water is a solvent for minerals and translocation
Water is used during photosynthesis to
manufacture food
Water gives cells shape (turgor)
Water
Extremes
With excess water roots
will suffocate.
Without water most
roots dry out and die.
Soil Aeration

Roots must have oxygen from the air to
convert stored food to energy (respiration).

Roots need oxygen to absorb essential
elements.
oxygen
carbon dioxide
Pores in the soil hold air.
Oxygen is most available in the top 18” of soil.
Lack of oxygen in the soil may be
caused by
Planted
too deep
Saturation
Compaction
Fill soil
Functions of Plant Roots
 Anchorage
 Absorption and transport
 Storage
 Production of chemicals
Anchorage
u
Roots hold plants
upright
u
Roots keep plants
stable as winds
blow against
them
Anchorage
Trees need healthy roots
for support and stability
Tree roots and anchorage
fail due to:
Excess water
Diseased roots
Excessive fill or compacted soil
Severed roots
Absorption and Transport
 Roots absorb water
and nutrients from the
soil
 Roots translocate
(move) water and
dissolved nutrients to
other plant parts
Small absorbing roots
are covered with fine
root hairs
Storage
 Roots store
reserves of sugars,
starches and other
materials
 Plants use stored
reserves for growth
and repair
Food stored in the
roots may be used to
produce stems, leaves
flowers and new roots.
Starch stored in roots
stains dark purple with
iodine.
Knowing where tree roots are located
can help us protect them and know
where to apply mulch, water, fertilizer
and other materials needed to promote
root growth
• root growth
• compacted soil
• low soil oxygen
• soil erosion
• excessive mulch
• physical objects
Reasons roots occur above ground
Some trees (mainly tropicals) have above ground roots
for support and absorption.
Tree Root Spread
Whether a younger or an
older tree, roots may
extend ...
… 2 to 4 times
beyond the drip line.
Root Spread Limitations
(buildings, containers, curbing, median strips, parking islands, tree pits
and other obstacles)
Plant Organs - The Shoot
 Consists of stems
and leaves.
 The shoot functions
primarily in support,
food and water
conduction, and food
manufacture.
Plant Organs - The Stem (Dicots)
 Nodes
 Points on a stem where a leaf or leaves are
attached.
 Spaces between nodes
are called Internodes.
 Buds
 Lateral buds at the base of
leaves.
 Terminal buds at the apex of stems.
 Adventitious buds on stems.
Plant Organs - The Stem
 The Stem
 The stem functions primarily
in support, food and water
conduction, and food
manufacture (when green).

Sometimes also stores food.

Can root at nodes (dicots).
The Stem - Monocots
 Palms, orchids, &
grasses are monocots
 vascular system
differs from dicots
Plant Organs - The Leaf
 The Leaf
Is a flattened or extended
portion of the stem.
 2 parts - the blade and the
petiole.
 veins appear as lines or
ridges
 Stomates (stomata) –
regulate gas
exchange &
moisture loss

Plant Organs - The Leaf
 Monocot Leaf
 Chief veins are parallel or
nearly so.
 Typically grasses, palms
 Dicot Leaf
 veins form a net-like
pattern.
 Commonly referred to as
“Broadleaves”.
Mark Shelby
Sarasota County Extension
Bruce Ide
Palm Beach County Extension
Bonnie Lee Appleton
Katherine Kilburne
Sybil Mays
Susan Ruiz-Evans
Virginia Polytechnic Institute and State University
Hampton Roads Agricultural Research and Extension
Center
Virginia Beach, Virginia