Chapter 9
Lecture Outline
Growth and
Development
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Outline

Introduction

Nutrients, Vitamins, and Hormones

Hormonal Interactions

Other Hormonal Interactions

Plant Movements

Photoperiodism

Cytochromes and Cryptochromes

A Flowering Hormone?

Temperature and Growth

Dormancy and Quiescence
Introduction

Growth - Irreversible increase in mass due to
division and enlargement of cells
• Determinate growth - Plant grows, stops growing and
dies in one season.
• Indeterminate growth - Plant or parts of plant grow
and continue to be active for several to many years.

Differentiation - Cells develop different forms
adapted to specific functions.

Development - Coordination of growth and
differentiation of a single cell into tissues and
organs
Nutrients, Vitamins, and Hormones

Nutrients - Furnish elements and energy for
plant growth and maintenance
• Obtained from air and soil

Vitamins - Organic molecules that
participate in catalyzed reactions, mostly by
functioning as electron acceptors or donor
• Synthesized in cell membranes and cytoplasm
• Required in small amounts for normal growth and
development
Nutrients, Vitamins, and Hormones

Hormones - Production dictated by genes.
• Mostly produced in actively growing regions
• Produced and active in smaller amounts than
vitamins and enzymes

Plant growth response results form signal
transduction pathway .
• Signaling molecule binds to receptor releasing
messenger molecule
• Eventually enzyme is produced, catalyzing
reaction and responding to environmental cue
Nutrients, Vitamins, and Hormones

Hormones can have multiple effects.

Hormones act by chemically binding to
specific receptors.
• Hormone-receptor association initiates effect.
• Triggers series of biochemical events, including
turning genes on and off
–

Biochemical events = Signal transduction
Major types of hormones: auxins,
gibberellins, cytokinins, abscisic acid,
ethylene
Nutrients, Vitamins, and Hormones
Plant Hormones

Auxins
• Auxin production occurs mainly in apical
meristems, buds, young leaves and actively
growing parts of plants.
• Similar structure to amino acid, tryptophan
• Plant responses vary according to concentration,
location, and other factors.
• Generally, monocots less sensitive than dicots
and shoots less sensitive than roots.
Nutrients, Vitamins, and Hormones
Plant Hormones

Auxins
• Some effects include:
–
Stimulate enlargement of cells by increasing cell wall
plasticity
–
–
Trigger production of other hormones
Cause dictyosomes to increase rate of secretion
–
Control some phases of respiration
–
Influence growth
–
Promote cell enlargement and stem growth, cell division
in cambium, initiation of roots and differentiation of cell
–
Delay development processes such as fruit and leaf
abscission, and fruit ripening
–
Inhibit lateral branching
Nutrients, Vitamins, and Hormones
Plant Hormones

Auxins
• Movement of auxins from cells where they
originate requires energy expenditure.
–
Movement is polar - Away from source
–
Move through parenchyma cells surrounding vascular
bundles
Nutrients, Vitamins, and Hormones
Plant Hormones

Auxins
• Natural occurring growth regulators include:
•
o
Indoleacetic acid (IAA)
o
Phenylacetic acid (PAA)
o
4-chloroindoleacetic acid (4-chloroIAA)
o
Indolebutyric acid (IBA)
Synthetic growth regulators include:
o Naphthalene acetic acid (NAA)
o 2,4-dichlorophenoxy acetic acid (2,4-D)
Nutrients, Vitamins, and Hormones
Plant Hormones

Gibberellins (GA)
• Named after a fungus that
produces it (Gibberella fujikuroi)
• 110 currently known gibberellins
• Movement is nonpolar.
• Most dicots and a few monocots
grow faster with an application of
GA.
–
Dramatically increases stem growth
• Involved in same regulatory
processes as auxins
Effect of gibberellins
on cabbage
Nutrients, Vitamins, and Hormones
Plant Hormones

Cytokinins
• Regulate cell division
• Synthesized in root tips and in germinating seeds
• Movement is nonpolar.
• If auxin present during cell cycle, cytokinins promote
cell division by speeding up progression from G2
phase to mitosis phase.
• Also play role in:
–
–
–
–
–
Cell enlargement
Differentiation of tissues
Development of chloroplasts
Stimulation of cotyledon growth
Delay of aging in leaves
Nutrients, Vitamins, and Hormones
Plant Hormones

Abscisic acid (ABA)
• Has inhibitory effect on stimulatory effects of
other hormones
• Synthesized in plastids from carotenoid pigments
• Movement is nonpolar.
• Common in fleshy fruits - Prevents seeds from
germinating while still on plant
• Helps leaves respond to excessive water loss
–
Interferes with transport or retention of potassium ions
in guard cells, causing stomata to close
Nutrients, Vitamins, and Hormones
Plant Hormones

Ethylene
• Produced by fruits, flowers, seeds, leaves and roots
• Produced from amino acid methionine
• Can trigger its own production
• Used to ripen
green fruits
–
Production almost
ceases in absence
of oxygen.
• Causes leaf
abscission
Ethylene from apple caused
abscission of holly leaves
Nutrients, Vitamins, and Hormones
Other Hormones or Related Compounds

Oligosaccharins
• Released from cell walls by enzymes - Influence
cell differentiation, reproduction, and growth in
plants

–
Produce effects at concentrations 1000x less than auxins
–
Effects are highly specific and responses are same in all
species.
Brassinosteroids
• Bind to receptors on cell surfaces
• Affect apical dominance, gravitropism, seed
germination
Hormonal Interactions

Apical dominance - Suppression of growth of
lateral (axillary) buds
• Believed to be brought about by auxin-like
inhibitor in terminal bud
• Strong in trees with conical shapes
–
Pines, spruces, firs
• Weak in trees that branch more often
–
Elms, ashes, willows
• If cytokinins applied in appropriate concentration
to axillary buds, they will begin to grow, even in
presence of terminal bud.
Hormonal Interactions

Senescence - Breakdown of cell components
and membranes, eventually leading to death
of cell
• Some studies have suggested certain plants
produce a senescence “factor.”
• Not certain of precise mechanisms involved

Other hormonal interactions
• Root and shoot development in tissue culture
regulated by auxins and cytokinins.
• Seed germination regulated by gibberellins and
ABA.
Plant Movements

Growth movements - Result from varying
growth rates in different parts of an organ
• Movements resulting
primarily from internal
stimuli:
–
–
Nutations - Spiraling
movements not visible
to eye
Nodding movements Side-to-side oscillations
o In bent hypocotyl of
bean - Facilitates
progress of plant
through soil
Nutation
Plant Movements

Growth Movements
Movements resulting primarily from internal
stimuli:
• Twining movements - Visible
spiraling in growth
–
–
Stems of flowering plants Morning glory
Tendrils
• Contraction movements
–
Contractile roots that pull
roots deeper
• Nastic movements - Non-
directional
• Epinasty - Permanent
downward bending
Tendril of
manroot
plant
Plant Movements
Growth Movements

Movements resulting from external stimuli:
• Tropisms - Permanent movements resulting from
external stimuli
–
Growth of a plant toward or away from a stimulus
–
Can be divided into three phases:
o
Initial perception - Organ receives greater stimulus
on one side.
o
Transduction - One or more hormones become(s)
unevenly distributed across organ.
o
Asymmetric growth - Result of greater cell
elongation on one side
Plant Movements

Growth Movements
Movements resulting from external stimuli:
• Phototropism - Growth movement toward or
away from light
–
Positive phototropism - Toward light
o
–
Negative phototropism - Away from
light
o
–
Shoots
Roots either insensitive or negatively
phototrophic.
Auxin migrates away from light, and
accumulates in greater amounts on
opposite side, promoting greater
elongation of cells on dark side.
Plant Movements

Growth Movements
Movements resulting from external stimuli:
• Gravitropism - Growth responses to stimulus of
gravity
–
–
–
Primary roots - Positively gravitropic
Shoots - Negatively gravitropic
Gravity may be perceived by amyloplasts in root cap, by
proteins on outside of plasma membrane, or by whole
protoplast.
o Auxin causes cell
elongation that
produces curvature
of root.
Negative gravitropism
Plant Movements

Growth Movements
Movements resulting from external stimuli:
• Other Tropisms:
–
Thigmotropism - Contact with solid object
o Twining
–
Chemotropism - Chemicals
o Germination of pollen grains
–
Thermotropism - Temperature
o Horizontal stems when cold in some weeds
–
Traumotropism - Wounding
–
Electrotropism - Electricity
–
Skototropism - Dark
–
Aerotropism - Oxygen
Plant Movements

Turgor movements - Result from changes in
internal water pressures and often initiated
by contact with objects outside of plant
• Leaf movement by pulvini
–
Pulvini - Special swellings
at base of leaf
o Sensitive plant, redwood
sorrel
–
Turgor contact movements
are not confined to leaves.
o Many flowers exhibit
movements of stamens
and other parts,
facilitating pollination.
Sensitive plant
Plant Movements

Turgor movements
“Sleep” movements Circadian rhythms
• Regular daily cycles
–
Leaves or petals fold in regular
daily cycles.
o Members of the legume family,
prayer plants
• Turgor movements, and stimuli of
light and temperature involved.
• Controlled by a biological “clock”
on approximately 24 hours cycles
–
Appear to be controlled internally
Circadian rhythm
in prayer plant
Plant Movements
Turgor movements

Solar tracking – Heliotropism-Leaves often
twist on their petioles in response to
illumination and become perpendicularly
oriented to light source.
• Blades oriented at right angles to sun.

Water conservation movements
• Bulliform cells - Special thin-walled cells in leaves
of many grasses that lose turgor and cause
leaves to roll up or fold during periods of
insufficient water
Plant Movements

Taxes (taxic movement) - Movement that
involves entire plant or reproductive cells.
• In several groups of plants and fungi, but not in
flowering plants
• Cell or organism, moves by flagella or cilia toward
or away from stimulus.
–
Chemotaxic - Chemicals
o Sperm in ferns swim toward chemical produced by
female reproductive structures.
–
Phototaxic - Light
–
Aerotaxic - Oxygen concentrations
Photoperiodism

Photoperiodism - Length of day (night)
directly related to onset of flowering.
• Short-day plants - Will not flower unless day
length is shorter than a critical period
–
Asters, poinsettias, ragweed, sorghums, strawberries
• Long-day plants - Will not flower unless periods of
light are longer than a critical period
–
Beets, larkspur, lettuce, potatoes, spinach, wheat
Photoperiodism

Intermediate-day plants - Will not flower if days
too short, or too long
• Several grasses

Day-neutral plants - Will flower under any daylength, provided there is minimum amount of
light necessary for normal growth
• Tropical plants, beans, carnations, cotton, roses,
tomatoes

Vegetative activities affected by phototropisms:
• Dormancy of buds
• Germination of seeds

Prepares plants for seasons
Phytochromes and Cryptochromes

Phytochromes - Pigments that control
photoperiodism
• Pale blue proteinaceous pigments that absorb light
• Mostly in meristematic tissues
• Two stable forms:
–
–
–
Pr - Absorbs red light
Pfr - Absorbs far-red light
When either form absorbs light - Converted to other form
Phytochromes and Cryptochromes

Phytochromes
• Play role in other plant responses:
–

Plant development, changes in plastids, production of
anthocyanins, and detection of shading
Cryptochromes - Blue, light-sensitive
pigments that play a role in circadian
rhythms and interact with phytochromes to
control reactions to light
A Flowering Hormone?

Flowering Locus T (FT)-gene produced by
Arabidopsis thaliana associated with
flowering
• When phytochrome senses a short photoperiod,
it represses CONSTANS gene
• When phytochrome senses a long photoperiod, it
activates FT
• FT is transported from leaves, to shoot apical
meristem, where it stimulates flowering.
Temperature and Growth

Each plant species has optimum temperature
for growth and minimum temperature below
which growth will not occur.
• Thermoperiod - Optimum night and day
temperatures
• Optimum temperatures may change with growth
stage of plant.
• Lower night temperatures often result in higher
sugar content and in greater root growth.
• Growth of many field crops is roughly proportional
to prevailing temperatures.
Dormancy and Quiescence

Dormancy - Period of growth inactivity in
seeds, buds, bulbs, and other plant organs
even when temperature, water, or day length
would typically cause growth

Quiescence - State in which seed cannot
germinate unless environmental conditions
normally required for growth are present

After-ripening - Factors that control change
from dormancy to germination in seeds

Stratification - Artificially breaking dormancy
Review

Introduction

Nutrients, Vitamins, and Hormones

Hormonal Interactions

Other Hormonal Interactions

Plant Movements

Photoperiodism

Cytochromes and Cryptochromes

A Flowering Hormone?

Temperature and Growth

Dormancy and Quiescence