Chp9 growthanddevelopment

VEGETATIVE GROWTH AND
DEVELOPMENT
 Shoot and Root Systems
 Crop plants must yield for profit
 Root functions
 Anchor
 Absorb
 Conduct
 Store

As the shoot system enlarges, the root system must
also increase to meet demands of leaves/stems

MEASURING GROWTH

 Increase in fresh weight
 Increase in dry weight
 Volume
 Length
 Height
 Surface area

MEASURING GROWTH

 Definition:

 Size increase by cell division and enlargement,
including synthesis of new cellular material and
organization of subcellular organelles.

MEASURING GROWTH

 Classifying shoot growth

 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

 Annuals

 Herbaceous (nonwoody) plants
 Complete life cycle in one growing season
 See general growth curve; fig. 9-1
 Note times of flower initiation
 See life cycle of angiosperm annual; fig. 9-3
 Note events over 120-day period


 Biennials

 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


 Perennials

 Either herbaceous or woody
 Herbaceous roots live indefinitely (shoots can)
 Shoot growth resumes in spring from adventitious buds in
crown
 Many grown as annuals
 Woody roots and shoots live indefinitely
 Growth varies with annual environment and zone
 Pronounced diurnal variation in shoot growth; night greater

ROOT GROWTH PATTERNS

 Variation in pattern with species and season
 Growth peaks in spring, late summer/early fall
 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

 Meristems
 Dicots
 Apical meristems – vegetative buds
 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

 Meristems (cont)

 Secondary growth in woody perennials
 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
 DNA directs growth and differentiation
 Enzymes catalyze biochemical reactions
 Structural genes
 Genes involved in protein synthesis
 Operator genes
 Regulate structural genes
 Regulatory genes
 Regulate operator genes

GENETIC FACTORS AFFECTING
GROWTH AND DEVELOPMENT
 What signals trigger these genes?

 Believed to include:
 Growth regulators
 Inorganic ions
 Coenzymes
 Environmental factors; e.g. temperature, light

 Therefore . . .
 Genetics directs the final form and size of the plant as
altered by the environment

ENVIRONMENTAL FACTORS
INFLUENCING PLANT GROWTH
 Light
 Temperature
 Water
 Gases

 Light
 Sun’s radiation
 not all reaches earth; atmosphere absorbs much
 visible (and some invisible) rays pass, warming surface
 reradiation warms atmosphere
 Intensity
 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

 Light (cont)
 narrow band affects plant photoreaction processes
 PAR (Photosynthetically Active Radiation)
 400-700nm
 stomates regulated by red (660nm), blue (440nm)
 photomorphogenesis – shape determined by light
 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

 Light (cont)
 importance of phytochrome in plant responses
 plants detect ratio of red:far-red light
 red light – full sun
 yields sturdy, branched, compact, dark green plants
 far-red light – crowded, shaded fields/greenhouses
 plants tall, spindly, weak, few branches; leaves light green

 Light (cont)
 Phototropism – movement toward light
 hormone auxin accumulates on shaded side
 cell growth from auxin effect bends plant
 blue light most active in process
 pigment uncertain

 Light (cont)
 Photoperiodism – response to varying length of
light and dark
 shorter days (longer nights)
 onset of dormancy
 fall leaf color
 flower initiation in strawberry, poinsettia, chrysanthemum
 tubers/tuberous roots begin to form
 longer days (shorter nights)
 bulbs of onion begin to form
 flower initiation in spinach, sugar beets, winter barley

 Temperature
 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
 opaque cover reduces radiation heat loss
 burning smudge pots radiate heat to citrus trees
 wind machines circulate warm air from temperature
inversions

 Water
 most growing plants contain about 90% water
 amount needed for growth varies with plant and
light intensity
 transpiration drives water uptake from soil
 water pulled through xylem
 exits via stomates
 evapotranspiration - total loss of water from soil
 loss from soil evaporation and plant transpiration

 Gases
 Nitrogen is most abundant
 Oxygen and carbon dioxide are most important
 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
 Phasic development
 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
 Juvenility
 terminated by flowering and fruiting
 may be extensive in certain forest species
 Maturity
 loss or reduction in ability of cuttings to form adventitious
roots
 Physiologically related
 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
 Life spans among plants differ greatly
 range from few months to thousands of years
 e.g. bristlecone pine (over 4000 years old)
 e.g. California redwoods (over 3000 years old)
 clones should be able to exist indefinately
 Senescence
 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
 Phases
 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
 Flower induction and initiation

 What causes a plant to flower?

 Daylength (photoperiod)

 Low temperatures (vernalization)

 Neither

REPRODUCTIVE GROWTH
AND DEVELOPMENT
 Photoperiodism (see table 9-5)
 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
 Market may dictate; consumer’s expectations
associated with seasons, e.g. poinsettias at
Christmas

REPRODUCTIVE GROWTH
AND DEVELOPMENT
 Photoperiodism (cont)
 Stimulus transported from leaves to meristems
 Cocklebur
 Leaf removal – failed to flower
 Isolated leaf, dark exposure – flowering initiated
 Believed to be hormone related
 Interruption of night with light affects flowering
 Cocklebur
 Red light, 660 nm, inhibits
 Far-red, 730 nm, restores
 Discovery of Phytochrome

REPRODUCTIVE GROWTH
AND DEVELOPMENT
 Low temperature induction
 Vernalization
 “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

 Flower development
 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

 Pollination
 Transfer of pollen from anther to stigma
 May be:
 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

 Self-fertile plant produces fruit and seed with
its own pollen
 Self-sterile plant requires pollen from another
cultivar to set fruit and seed
 Often due to incompatibility; pollen will not grow
through style to embryo sac
 Sometimes cross-pollination incompatibility

REPRODUCTIVE GROWTH
AND DEVELOPMENT
 Pollen transferred by:
 Insects; chiefly honeybees
 Bright flowers
 Attractive nectar
 Wind
 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
 What if pollination and fertilization fail to
occur?
 Fruit and seed don’t develop
 Exception: Parthenocarpy
 Formation of fruit without pollination/fertilization
 Parthenocarpic fruit are seedless
 e.g. ‘Washington Navel’ orange, many fig cultivars
 Note: not all seedless fruits are parthenocarpic
 Certain seedless grapes – fruit forms but embryo aborts

REPRODUCTIVE GROWTH
AND DEVELOPMENT

 Fertilization
 Angiosperms (flowering plants)
 Termed double fertilization
 Gymnosperms (cone-bearing plants)
 Staminate, pollen-producing cones
 Ovulate cones produce “naked” seed on cone scales

REPRODUCTIVE GROWTH
AND DEVELOPMENT
 Fruit setting
 Accessory tissues often involved
 e.g. enlarged, fleshy receptacle of apple and pear
 True fruit is enlarged ovary
 Not all flowers develop into fruit
 Certain plant hormones involved
 Optimum level of fruit setting
 Remove excess by hand, machine, or chemical
 Some species self-thinning; Washington Navel Orange
 Temperature strongly influences fruit set

REPRODUCTIVE GROWTH
AND DEVELOPMENT

 Fruit growth and development
 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

 Plant hormones are natural
 Plant growth regulators include:
 Plant hormones (natural)
 Plant hormones (synthetic)
 Non-nutrient chemicals
 Five groups of natural plant hormones:
 Auxins, Gibberellins, Cytokinins, Ethylene, and
Abscisic acid

Chp9 growthanddevelopment

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