This document discusses plant growth and development, including: 1. It describes vegetative growth patterns in shoots and roots of annuals, biennials, and perennials. 2. Environmental factors like light, temperature, water, and gases influence plant growth. Light intensity, day length, and temperature correlate with seasonal growth patterns. 3. Reproductive growth involves phases from flower induction through fruit maturation. Flowering is induced by day length (photoperiodism) in some plants and temperature (vernalization) in others.

1. GROWTH AND
DEVELOPMENT

2. 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

3. MEASURING GROWTH
 Increase in fresh weight
 Increase in dry weight
 Volume
 Length
 Height
 Surface area

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

5. 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

6. 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

8. 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

9. 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

10. 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

11. 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

12. 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

13. 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

14. 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

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

16. 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

17. 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

18. 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

19. 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

20. 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

21. 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

22. 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

23. 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

24. 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

25. 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

26. 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

27. 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

28. REPRODUCTIVE GROWTH
AND DEVELOPMENT
 Flower induction and initiation
 What causes a plant to flower?
 Daylength (photoperiod)
 Low temperatures (vernalization)
 Neither

29. 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

31. 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

33. 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

34. 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

35. 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)

36. 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

37. 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

38. 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

39. 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

40. 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

41. 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)

42. 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