Transcript GROWTH AND DEVELOPMENT

GROWTH AND
DEVELOPMENT
VEGETATIVE GROWTH AND
DEVELOPMENT
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Shoot and Root Systems
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Crop plants must yield for profit
Root functions
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Anchor
Absorb
Conduct
Store
As the shoot system enlarges, the root system must
also increase to meet demands of leaves/stems
MEASURING GROWTH
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Increase in fresh weight
Increase in dry weight
Volume
Length
Height
Surface area
MEASURING GROWTH
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Definition:
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Size increase by cell division and enlargement,
including synthesis of new cellular material and
organization of subcellular organelles.
MEASURING GROWTH
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Classifying shoot growth
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Determinate – flower buds initiate terminally;
shoot elongation stops; e.g. bush snap beans
Indeterminate – flower buds born laterally;
shoot terminals remain vegetative; e.g. pole beans
SHOOT GROWTH PATTERNS
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Annuals
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Herbaceous (nonwoody) plants
Complete life cycle in one growing season
See general growth curve; fig. 9-1
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Note times of flower initiation
See life cycle of angiosperm annual; fig. 9-3
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Note events over 120-day period
SHOOT GROWTH PATTERNS
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Biennials
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Herbaceous plants
Require two growing seasons to complete their
life cycle (not necessarily two full years)
Stem growth limited during first growing season;
see fig. 9-4; Note vegetative growth vs. flowering
e.g. celery, beets, cabbage, Brussels sprouts
SHOOT GROWTH PATTERNS
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Perennials
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Either herbaceous or woody
Herbaceous roots live indefinitely (shoots can)
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Shoot growth resumes in spring from adventitious buds in
crown
Many grown as annuals
Woody roots and shoots live indefinitely
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Growth varies with annual environment and zone
Pronounced diurnal variation in shoot growth; night greater
ROOT GROWTH PATTERNS
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Variation in pattern with species and season
Growth peaks in spring, late summer/early fall
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Spring growth from previous year’s foods
Fall growth from summer’s accumulated foods
Some species roots grow during winter
Some species have some roots ‘resting’ while,
in the same plant, others are growing
HOW PLANTS GROW
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Meristems
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Dicots
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Apical meristems – vegetative buds
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shoot tips
axils of leaves
Cells divide/redivide by mitosis/cytokinesis
Cell division/elongation causes shoot growth
Similar meristematic cells at root tips
HOW PLANTS GROW
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Meristems (cont)
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Secondary growth in woody perennials
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Increase in diameter
 due to meristematic regions
vascular cambium
 xylem to inside, phloem to outside
cork cambium
 external to vascular cambium
 produces cork in the bark layer
GENETIC FACTORS AFFECTING
GROWTH AND DEVELOPMENT
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DNA directs growth and differentiation
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Structural genes
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Genes involved in protein synthesis
Operator genes
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Enzymes catalyze biochemical reactions
Regulate structural genes
Regulatory genes
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Regulate operator genes
GENETIC FACTORS AFFECTING
GROWTH AND DEVELOPMENT
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What signals trigger these genes?
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Believed to include:
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Growth regulators
Inorganic ions
Coenzymes
Environmental factors; e.g. temperature, light
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Therefore . . .
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Genetics directs the final form and size of the plant as
altered by the environment
ENVIRONMENTAL FACTORS
INFLUENCING PLANT GROWTH
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Light
Temperature
Water
Gases
ENVIRONMENTAL FACTORS
INFLUENCING PLANT GROWTH
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Light
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Sun’s radiation
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not all reaches earth; atmosphere absorbs much
visible (and some invisible) rays pass, warming surface
reradiation warms atmosphere
Intensity
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high in deserts; no clouds, dry air
low in cloudy, humid regions
earth tilted on axis; rays strike more directly in summer
day length varies during year due to tilt
ENVIRONMENTAL FACTORS
INFLUENCING PLANT GROWTH
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Light (cont)
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narrow band affects plant photoreaction processes
PAR (Photosynthetically Active Radiation)
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400-700nm
stomates regulated by red (660nm), blue (440nm)
photomorphogenesis – shape determined by light
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controlled by pigment phytochrome
phytochrome absorbs red (660nm) and far-red (730nm)
but not at same time
pigment changes form as it absorbs each wavelength
ENVIRONMENTAL FACTORS
INFLUENCING PLANT GROWTH
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Light (cont)
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importance of phytochrome in plant responses
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plants detect ratio of red:far-red light
red light – full sun
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yields sturdy, branched, compact, dark green plants
far-red light – crowded, shaded fields/greenhouses
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plants tall, spindly, weak, few branches; leaves light green
ENVIRONMENTAL FACTORS
INFLUENCING PLANT GROWTH
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Light (cont)
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Phototropism – movement toward light
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hormone auxin accumulates on shaded side
cell growth from auxin effect bends plant
blue light most active in process
pigment uncertain
ENVIRONMENTAL FACTORS
INFLUENCING PLANT GROWTH
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Light (cont)
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Photoperiodism – response to varying length of
light and dark
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shorter days (longer nights)
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onset of dormancy
fall leaf color
flower initiation in strawberry, poinsettia, chrysanthemum
tubers/tuberous roots begin to form
longer days (shorter nights)
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bulbs of onion begin to form
flower initiation in spinach, sugar beets, winter barley
ENVIRONMENTAL FACTORS
INFLUENCING PLANT GROWTH
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Temperature
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correlates with seasonal variation of light intensity
temperate-region growth between 39°F and 122°F
high light intensity creates heat; sunburned
low temp injury associated with frosts; heat loss
by radiation contributes
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opaque cover reduces radiation heat loss
burning smudge pots radiate heat to citrus trees
wind machines circulate warm air from temperature
inversions
ENVIRONMENTAL FACTORS
INFLUENCING PLANT GROWTH
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Water
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most growing plants contain about 90% water
amount needed for growth varies with plant and
light intensity
transpiration drives water uptake from soil
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water pulled through xylem
exits via stomates
evapotranspiration - total loss of water from soil
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loss from soil evaporation and plant transpiration
ENVIRONMENTAL FACTORS
INFLUENCING PLANT GROWTH
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Gases
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Nitrogen is most abundant
Oxygen and carbon dioxide are most important
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plants use CO2 for photosynthesis; give off O2
plants use O2 for respiration; give off CO2
stomatal opening and closing related to CO2 levels?
oxygen for respiration limited in waterlogged soils
increased CO2 levels in atmosphere associated with
global warming
additional pollutants harm plants
PHASE CHANGE: JUVENILITY,
MATURATION, SENESCENCE
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Phasic development
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embryonic growth
juvenility
transition stage
maturity
senescence
death
During maturation, seedlings of many woody
perennials differ strikingly in appearance at
various stages of development
PHASE CHANGE: JUVENILITY,
MATURATION, SENESCENCE
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Juvenility
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Maturity
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terminated by flowering and fruiting
may be extensive in certain forest species
loss or reduction in ability of cuttings to form adventitious
roots
Physiologically related
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lower part of plant may be oldest chronologically, yet be
youngest physiologically (e.g. some woody plants)
top part of plant may be youngest in days, yet develop into
the part that matures and bears flowers and fruit
AGING AND SENESCENCE
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Life spans among plants differ greatly
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range from few months to thousands of years
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e.g. bristlecone pine (over 4000 years old)
e.g. California redwoods (over 3000 years old)
clones should be able to exist indefinately
Senescence
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a physiological aging process in which tissues in an
organism deteriorate and finally die
considered to be terminal, irreversible
can be postponed by removing flowers before seeds start
to form
REPRODUCTIVE GROWTH
AND DEVELOPMENT
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Phases
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Flower induction and initiation
Flower differentiation and development
Pollination
Fertilization
Fruit set and seed formation
Growth and maturation of fruit and seed
Fruit senescence
REPRODUCTIVE GROWTH
AND DEVELOPMENT
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Flower induction and initiation
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What causes a plant to flower?
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Daylength (photoperiod)
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Low temperatures (vernalization)
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Neither
REPRODUCTIVE GROWTH
AND DEVELOPMENT
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Photoperiodism (see table 9-5)
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Short-day plants (long-night; need darkness)
Long-day plants (need sufficient light)
Day-neutral plants (flowering unaffected by period)
Change from vegetative to reproductive
Manipulations enable year-round production
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Market may dictate; consumer’s expectations
associated with seasons, e.g. poinsettias at
Christmas
REPRODUCTIVE GROWTH
AND DEVELOPMENT
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Photoperiodism (cont)
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Stimulus transported from leaves to meristems
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Cocklebur
Leaf removal – failed to flower
Isolated leaf, dark exposure – flowering initiated
Believed to be hormone related
Interruption of night with light affects flowering
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Cocklebur
Red light, 660 nm, inhibits
Far-red, 730 nm, restores
Discovery of Phytochrome
REPRODUCTIVE GROWTH
AND DEVELOPMENT
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Low temperature induction
Vernalization
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“making ready for spring”
Any temperature treatment that induces or
promotes flowering
First observed in winter wheat; many biennials
Temperature and exposure varies among species
Note difference/relationship to dormancy
Many plants do not respond to changed
daylength or low temperature; agricultural
REPRODUCTIVE GROWTH
AND DEVELOPMENT
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Flower development
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Stimulus from leaves to apical meristem changes
vegetative to flowering
Some SDPs require only limited stimulus to
induce flowering; e.g. cocklebur – one day (night)
Once changed the process is not reversible
Environmental conditions must be favorable for
full flower development
REPRODUCTIVE GROWTH
AND DEVELOPMENT
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Pollination
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Transfer of pollen from anther to stigma
May be:
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Same flower (self-pollination)
Different flowers, but same plant (self-pollination)
Different flowers/plants, same cultivar (self-pollination)
Different flowers, different cultivars (cross-pollination)
REPRODUCTIVE GROWTH
AND DEVELOPMENT
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Self-fertile plant produces fruit and seed with
its own pollen
Self-sterile plant requires pollen from another
cultivar to set fruit and seed
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Often due to incompatibility; pollen will not grow
through style to embryo sac
Sometimes cross-pollination incompatibility
REPRODUCTIVE GROWTH
AND DEVELOPMENT
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Pollen transferred by:
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Insects; chiefly honeybees
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Wind
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Bright flowers
Attractive nectar
Important for plants with inconspicuous flowers
e.g. grasses, cereal grain crops, forest tree species, some
fruit and nut crops
Other minor agents – water, snails, slugs, birds, bats
REPRODUCTIVE GROWTH
AND DEVELOPMENT
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What if pollination and fertilization fail to
occur?
Fruit and seed don’t develop
Exception: Parthenocarpy
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Formation of fruit without pollination/fertilization
Parthenocarpic fruit are seedless
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e.g. ‘Washington Navel’ orange, many fig cultivars
Note: not all seedless fruits are parthenocarpic
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Certain seedless grapes – fruit forms but embryo aborts
REPRODUCTIVE GROWTH
AND DEVELOPMENT
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Fertilization
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Angiosperms (flowering plants)
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Termed double fertilization
Gymnosperms (cone-bearing plants)
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Staminate, pollen-producing cones
Ovulate cones produce “naked” seed on cone scales
REPRODUCTIVE GROWTH
AND DEVELOPMENT
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Fruit setting
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Accessory tissues often involved
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Not all flowers develop into fruit
Certain plant hormones involved
Optimum level of fruit setting
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e.g. enlarged, fleshy receptacle of apple and pear
True fruit is enlarged ovary
Remove excess by hand, machine, or chemical
Some species self-thinning; Washington Navel Orange
Temperature strongly influences fruit set
REPRODUCTIVE GROWTH
AND DEVELOPMENT
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Fruit growth and development
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After set, true fruit and associated tissues begin to
grow
Food moves from other plant parts into fruit tissue
Hormones from seeds and fruit affect growth
Auxin relation in strawberry fruits
Gibberellins in grape (fig. 9-21, 9-22)
Patterns of growth vary with fruits (fig. 9-16, 9-17)
PLANT GROWTH REGULATORS
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Plant hormones are natural
Plant growth regulators include:
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Plant hormones (natural)
Plant hormones (synthetic)
Non-nutrient chemicals
Five groups of natural plant hormones:
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Auxins, Gibberellins, Cytokinins, Ethylene, and
Abscisic acid