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