GROWTH AND DEVELOPMENT
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
SHOOT GROWTH PATTERNS 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
SHOOT GROWTH PATTERNS 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
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 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