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

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

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

 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

 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

 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

 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

 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

ENVIRONMENTAL FACTORS
INFLUENCING PLANT GROWTH
 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

ENVIRONMENTAL FACTORS
INFLUENCING PLANT GROWTH
 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

ENVIRONMENTAL FACTORS
INFLUENCING PLANT GROWTH
 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

ENVIRONMENTAL FACTORS
INFLUENCING PLANT GROWTH
 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

ENVIRONMENTAL FACTORS
INFLUENCING PLANT GROWTH
 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

ENVIRONMENTAL FACTORS
INFLUENCING PLANT GROWTH
 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

ENVIRONMENTAL FACTORS
INFLUENCING PLANT GROWTH
 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

ENVIRONMENTAL FACTORS
INFLUENCING PLANT GROWTH
 Gases

Nitrogen is most abundant

Oxygen and carbon dioxide are most important





 plants use CO
2 for photosynthesis; give off O
2 plants use O
2 for respiration; give off CO
2 stomatal opening and closing related to CO
2 levels?
oxygen for respiration limited in waterlogged soils increased CO
2 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



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 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