1. Plant Growth: an irreversible change in the size of a cell, organ or
whole organism.
Differentiation: Cells taking on specialized form and function.
Plant Development: the orderly and progressive change from seed
germination through juvenility, maturity, flowering and fruiting.
6. Male and Female Gametophyte
Gametophyte – embryo sac
Gametophyte – anther
Gamete – egg
Gamete – two sperm cells (in pollen grain or tube)
Male
Female
16. Simplified Structure of A Mature Seed
Seed coat
Embryo
Endosperm
Seed coat is dead tissue.
It protects everything
inside it.
Embryo is a minute
plant .
Endosperm provides energy
for seed germination and
early seedling growth.
17. (1) How is a seed formed?
(2) How does a seed become a seedling?
(3) How is shoot formed?
(4) How is root formed?
(5) How is a flower formed?
18. Dry seeds Imbibed seeds
Water Uptake: the First Event in Germination
30. Causes of Physiological
Dormancy
• Covering restricts oxygen
• Inhibitors in coverings
• Embryo cannot break through physical barriers
• Endosperm restrict embryo growth
• Interaction between embryo and covering
• Abies alba, Castanea sativa, Corylus avellana, Euonymus
europaeus, Juglans nigra, Juglans regia, Juniperus,
Prunus avium,Rhamnus frangula, Vaccinium myrtillus
• Carpinus requires warm followed by cold stratification
• Elaeagnus umbellata- chemicals shortened prechilling &
increase germination
31. Nondeep Physiological
Dormancy
• Germinate over a narrow range of temperatures
• Excised embryos usually grow
• Broken by short periods of prechilling
• Require germination temperature above 15°C
• Broken by chemicals- potassium nitrate, thiourea,
kinetin, ethylene, gibberellins
• Light required for germination
• Arbutus unedo –can germinate in dark
• Ulmus glabra- no prechill
• Vaccinium- long period of light required, GA
reduces length of light
32. Intermediate Physiological Dormancy
• Excised embryos will grow
• As much as 6 months prechilling needed
• Gibberellins, kinetin, thiourea can shorten
prechilling requirement
• Acer negundo, Acer pseudoplatanus, Acer
saccharum, Corylus avellana, Fraxinus
americana, Fraxinus pennsylvanica
• Fagus sylvatica – ethylene accelerated and
increased germination at 15°C, at 5°C
chemicals no better than water soak on
germination, GA3 increased germination of
unchilled seeds at 15°C, 10 weeks prechill
negate chemical effect (Seed Sci 2004, p21-33)
33. Deep Physiological Dormancy
• Excised embryos do not grow or produce
abnormal seedlings (Prunus will)
• Long prechill requirement
• Chemicals do not affect germination of intact
seeds
• Sorbus aucuparis – secondary dormancy
induced above 20°C, germinates best at 1-3°C
• Acer platanoides, Acer tartaricum, Malus
domestica,
• Prunus persica – 90 days prechill
• Prunus mahaleb – 100 days prechill
• 3 to 5°C best germination temperature for
Prunus mahaleb, Prunus padus
34. Morphological Dormancy
• Morphology of embryo not developed
• Temperate families- Apiaceae,
Ranunculaceae
• Tropical families – Annonacease,
Arecaceae, Degeneriaceae,
Lactoridaceae, Monimiaceae,
Myrsticaceae, Winteraceae
35. Morphophysiological Dormancy
• Underdeveloped embryos
• Embryo growth and dormancy break
required
• Embryo grows first then dormancy
broken or both at same time
• Vary warm, moist and cold
stratification periods
• Viburnum- epicotyl dormancy, warm
for radical then cold for epicotyl
• Fraxinus excelsior, Magnolia
acuminata
36. Physical Dormancy
• Present in 15 angiosperm families
• Large embryos with food reserve in embryo not
endosperm
• Hilum impermeable in Cercis siliquastrum
• Impermeable in seed coats- micropyle, hilum, chalazal
area, impermeable palisade cells
• Embryo is not dormant
• Air drying during development intensifies hardness
• Cytisus scoparius – dry heat(65°C) for 2 minutes, or
acid for 30 minutes
• Crataegus in warm climates only endocarp dormant
• Robinia pseudoacacia, Laburnum anagroides
37. Physical & Physiological Dormancy
• Embryo dormancy usually broken first
• Germinate at low temperatures (5, 10, 15°C)
• Prechilling breaks physiological dormancy
• Hot water, acid, or mechanical scarification
effective before prechilling
• Cercis siliquastrum – 16 weeks prechilling = 77%
germination(Jordan source)(2004 Seed Sci p
255-260)
• Cersis canadensis, Cotinus coggygria, Cotinus
obovatus, Sambuscus
• Tilia- endosperm is inhibitor, excised embryos
grow
• Crataegus – 3 month periods of cold-warm-cold-
warm-cold=55% germination, apomixis common
38. Chemical Dormancy
• Inhibitors in embryo, endosperm, seed
coat
• Leaching or seed coat removal
• Seed may have physiological dormancy
too so need prechilling
• Abscisic acid inhibits germination
when applied exogenously
• Nickel (20 mg/liter) increased
germination of Picea abies
39. Mechanical Dormancy
• Stony endocarps
• Embryos with deep physiological dormancy -
require long prechilling
• Anacardiaceae, Cornaceae, Juglandaceae,
Nyssaceae, Oleaceae
• Cornus sanguinea – 94% germination at 12 weeks
prechilling, 81% germination at 12 weeks warm +
12 weeks cold stratification(2004 Seed Sci p 1-4)
• Cornus mas- 18 week warm + 15-18 weeks cold
stratification (Tylkowski 1991)
• Cornaceae not morphologically dormant
• Elaeagnus angustifolia – snip both ends
• Rosaceae - warm maturation temperature prior
to collection reduced dormancy
40. Mattoral Germination
Conditions
• Mean optimum germination
temperature for trees about 21°C –
during cool season when soil is moist
• Mean optimum germination
temperature for shrubs about 19°C
• Shrub seed germinate in light and dark
• No shrub seed has morphological
dormancy (underdeveloped embyros)
41. Boreal & North Temperate Subalpine
• Pinus cembra- 90-270 days of
prechilling
• No morphological,
morphophysiological, physical
dormancy in species
• Pinus mugo, Picea abies –
nondormant
42. (1) How is a seed formed?
(2) How does a seed become a seedling?
(3) How is shoot formed?
(4) How is root formed?
(5) How is a flower formed?
49. From: PM Ray, “The Living Plant”
Apical dominance is a
phenomenon in which the
apical bud tends to
“dominate” stem growth in
the sense that all of the
axillary buds immediately
below it do not grow out to
form branches. Thus the
stem grows tall, not wasting
resources by growing wide.
The idea is that auxin
produced in the apical bud is
transported down the stem
and suppresses the
outgrowth of the lateral
(axillary) buds. If the tip is
cut off the auxin source is
removed and the buds begin
to develop into branches.
50. (1) How is a seed formed?
(2) How does a seed become a seedling?
(3) How is shoot formed?
(4) How is root formed?
(5) How is a flower formed?
51. Root Systems
Taproot system: characterized by
having one main root (the taproot)
from which smaller branch roots
emerge. When a seed germinates,
the first root to emerge is the radicle,
or primary root. In conifers and
most dicots, this radicle develops
into the taproot.
Fibrous root system: characterized by
having a mass of similarly sized roots. The
radicle from a germinating seed is short lived
and is replaced by adventitious roots.
Adventitious roots are roots that form on
plant organs other than roots. Most monocots
have fibrous root systems.
52. Root tip has 4 developmental zones
Root cap: Protects RAM and push
Meristematic zone: Primary root
Elongation zone: Rapid cell
elongation, rate of division
decreases with distance from
meristem
Maturation zone: Cells get their
mature differentiated features.
No lateral organs produced from apical
meristem to avoid hindrance in soil
penetration
Branch roots arise from non
growing region
Root System development
53. Cells of the root epidermis develop projections called root hairs. These
elongate by “tip growth” and increase surface area for water and mineral
uptake. Root hairs are found away from the root tip, in the region of
maturation.
Note that the root hair develops as an
outgrowth from individual epidermal
cells; that is, the root hair is not a cell
separate from the epidermal cell. The
Figure shows (bottom to top) four
stages of root hair development: cell
specification, root hair initiation, tip
growth, and maturation.
