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Seeds and Seed Germination. Seeds and seed germination. Pollination. Fertilization. Embryo development. Mature seed. Seeds are normally the product of sexual reproduction. Seeds are for propagation. The biological function of seeds is for propagation of the species - PowerPoint PPT Presentation
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Seeds and Seed GerminationSeeds and Seed Germination
Seeds and seed germinationSeeds and seed germination
Seeds are normally the product of sexual reproduction
Pollination
Fertilization
Embryo development
Mature seed
Seeds are for propagationSeeds are for propagation
The biological function of seeds is for propagation of the species
How does seeds help in propagation of the species?
Diversity among seedsDiversity among seeds Seeds are very diverse in term of size:
– Begonia seed weigh 10-20 micrograms
– Coconuts weigh more than a kilogram
Thousands of Begonia seeds
Diversity among seedsDiversity among seedsIn terms of
adaptation to survive various environments until conditions are favorable for germination
In terms of method of dispersal
Seeds are for propagationSeeds are for propagation
Protect the zygote against physically injury Store foods for seedling-- before it becomes
independent Remain dormant to survive harsh environmentDisperse the seeds to capitalize on their genetic
variabilityRespond to environment cues and germinate at
the right time and place
Seeds are alive!Seeds are alive!To function in propagation, seeds must be aliveSeeds respire, albeit slowly
– consume O2, produce CO2 and H2O
Seeds have a finite lifespanthey cannot be stored indefinitely
Which kind of seeds can remain viable longer? Seeds of tropical plant or temperate plant?
Seeds are alive!Seeds are alive!Seeds of many tropical plants remain viable
for only a short time, a few days– Tropical plants grow in environments that do not
have a winter season through which seeds must survive before the favorable growing conditions of spring arrive
General features of seedsGeneral features of seeds
Embryo– Root and shoot, in a miniature form
Food reserves– Allow seedling to grow before it is capable of
performing photosynthesis
Seed coat– Provides protection from the environment
Monocots and DicotsMonocots and DicotsFlowering plants (angiosperms): Dicotyledonous plants with two seed leavesMonocotyledonous plants with one seed leaf
Angiospermsflowering plants
Dicots200,000 species
Monocots50,000 species
includes beans, roses, cacti, melons, citrus
includes grasses, lilies, orchids, palms
Seed structureSeed structure
Cotyledon
Plumule
Radicle
Micropyle
Seed coat or testa
Endospermous and non-Endospermous and non-Endospermous seedsEndospermous seeds
Takes place in the fruit on the parent plant Endospermous seeds: Retain the endosperm tissue,
and is surrounded by a layer of living cells, the aleurone layer.
Non-endospermous seeds: The endosperm tissue is absorbed by the cotyledons. The cotyledons then become the food reserve for the seed.
Endospermous or non-Endospermous or non-Endospermous seeds?Endospermous seeds?
Endospermous and non-Endospermous and non-Endospermous seedsEndospermous seeds
A LS of maize grain / fruitA LS of maize grain / fruit
• It is a phenomenon in certain seeds in which they would not germinate if given an optimal condition ( water, oxygen, optimum temperature ).
• Dormancy can be seen in seeds ( eg: legumes ), buds, spore & food storage organs ( tubers ).
• Due to many factors include:i. Lack of oxygenii. Drynessiii. Presence of substances that inhibit germination
SEED DORMANCYSEED DORMANCY
CHAPTER : GROWTH
GROWTH UNDER EXTREME CONDITIONGROWTH UNDER EXTREME CONDITION
DORMANCY• A period in the life cycle of many animals & plants when their
metabolic activities become minimum & growth stop.
• Is a resting stage• It can occur in the adult, egg, pupa, spore or seed stage.
• A way of protecting an organism against unfavourable conditions such as insufficient food, cold ( winter ) & dry ( drought ).
• It is controlled by hormones that ~ response to physiological in plants & animals ~ affecting the behaviour in animals
What physiological changes What physiological changes lead to dormancylead to dormancy
Metabolism fallsNumber of organelles per cell _____Dehydration – water content _____ Vacuoles in cells _____ Food reserves become _____ _____ _____
What physiological changes What physiological changes lead to dormancylead to dormancy
Metabolism fallsNumber of organelles per cell fallsDehydration – water content fallsVacuoles in cells deflateFood reserves become dense crystalline
bodies
CHAPTER : GROWTH
SEED GerminationSEED GerminationDormancy of these seeds may be broken by one or
more of the following: (1)light, sunlight being the most effective; (2)low temperatures (1 to 5 degrees Celsius [33.8 to 41
degrees Fahrenheit]) for several weeks; (3)day/night fluctuating temperatures of 1 to 10 degrees
Celsius (41 to 50 degrees Fahrenheit); (4)chemicals, such as nitrate in the soil, or applied
hormones (gibberellins) in the laboratory; and (5)fire.
CHAPTER : GROWTH
Seeds that require light involves a receptor protein, phytochrome
Dormancy mechanism is related to the seeds’ natural environment
is particularly important for small, wind-dispersed weed seeds.
Seeds that need a period of low temperature
the cold winter may cause the parent plant to die, and thus remove competition for space in the spring.
The requirement for alternating temperatures
will prevent germination of seeds beneath dense vegetation because the latter dampens the day/night temperature fluctuations; these seeds will germinate only when there is little vegetation cover, again reducing competition with established plants.
The requirement for fire
CHAPTER : GROWTH
Seeds that require light involves a receptor protein, phytochrome
Dormancy mechanism is related to the seeds’ natural environment
Seeds that need a period of low temperature
The requirement for alternating temperatures
The requirement for fire
Maintaining dormancyMaintaining dormancyPhysical barriers
The seed coat (testa) is waxy = waterproof and impermeable to oxygen
Physical state – dehydratedChemical inhibitors present e.g. salts,
mustard oils, organic acids, alkaloidsGrowth promoters absent
The breaking of dormancyThe breaking of dormancy
Break down of barriersAbrasion of seed coat (soil particles)Decomposition of seed coat (soil microbes, gut enzymes)Cracking of seed coat (fire)
Change in physical state - rehydration
Destruction and dilution of inhibitors
Light, temperature, water Production of growth promoters
Seed Germination: Emergence of Radicle through Seed Coat
Water Warm TemperatureSo if you want to store seeds what are the conditions? Dry Cold
Dormant seeds need more than moisture and warmth:
Thick Seed Coat
Thin Seed Coat
Insufficient Development
Inhibitor: Abscisic Acid
Inhibitor: Phenolics
Scarification
Light
Soil Fungus Association
Stratification > Vernalization
Leaching by Repeated Rain
Kentucky Coffee Tree
Lettuce
Orchids
Most CT feral plants
Cacti
Darkor or Pea
Dormancy is caused by: Is overcome by: Example:
To break dormancy seeds need:
nick digestscrub firefreeze-thaw cycles
6 weeks at 4° C 20° C
GerminationGermination
STAGE EVENTSPREGERMINATI
ON(a) Rehydration – imbibition of water.(b) RNA activated & protein synthesis
starts.(c) Increased metabolism – increased
respiration.(d) Hydrolysis (digestion) of food reserves
by enzymes.(e) Induction of cell division & cell growth.
GERMINATION (a) Rupture of seed coat.(b) Emergence of seedling, usually radicle
first.POST
GERMINATION
(a) Growth of root and shoot axis. Transport of materials from food stores to growing axis.
(b) Senescence (aging) of food storage tissues.
Stages leading to cell divisionStages leading to cell division
Mitchondria reconstituted Soluble sugars
RespirationInitially
anaerobicLater aerobicATP
RNA activated
Protein synthesis (0.5h)
Enzymes (proteins)
Mitosis (70h)
DNA synthesis (45h)
http://www.rbgsyd.nsw.gov.au/
Mobilization of food Mobilization of food reservesreserves
Control by growth promotors such as gibberellin and growth inhibitors such as abscisic acid
These directly affect the genes for enzyme synthesis or the activity of the enzymes themselves
The growth substances are affected by environmental factors (e.g. light, temperature, humidity)
The control of food reserve The control of food reserve hydrolysishydrolysis
Negative feedback control of enzymes
The action of the enzyme also limited by substrateOnce all the starch in an amyloplast is hydrolysed
the enzyme stops workTherefore the release of the stored food is
adjusted to suite the demand
Starch + H20 Maltose - amylase
Negative feedback
Carbohydrates
Starches(amylopectin & amylose)
AmylasesMaltose and
glucose
Proteins e.g. Zein Proteases Amino acids
Lipids Oils Lipases Fatty acids & glycerol
The mobilisation of food The mobilisation of food reservesreserves
The food reserves are stored as large insoluble macromolecules
They are hydrolysed using enzymes to smaller soluble molecules for transport
GAABAABAABA
Light, chilling or
water (rain) trigger the
inactivation of ABA, which
makes dormant
seeds able to germinate.
Triggering factors for germination
GA
After seeds take up water, GA is released from the embryo to signal aleurone.
-amylase
The aleurone responds by synthesizing and secreting digestive enzymes (-amylase) to hydrolyze stored
nutrients in the endosperm.
Nutrients (ex. sugars) absorbed from the endosperm by the scutellum (cotyledon) are
consumed by the seedling during germination.
The growth of seedling starting with the roots first, then shoot growth follows.
Barley Seed Germination
Fruit+Seed CoatEndospermAleurone Layer
Storage Protein
Amino Acids
hydr
olys
is
trans
latio
n
trans
cripti
on
hydro
lysis
starch
sugar
-amylase
RNA
DNA GA
imbibition
water
radicle apex
shoot apex
grow
th
cotyledon monocot
maltose
Embryo
exocytosis
Capsella Seed:
Seed Coat
Endosperm
EmbryoShoot Apex
Cotyledons - dicot
Hypocotyl
Radicle
Root Apex
Micropyle
Lettuce Seed Germination
660 nm
730 nmdark
Seed Coat
trans
latio
n
trans
cripti
on
hydrolysis starch
sugar
-amylase
RNA
DNA
imbibition
water
radicle apex
shoot apex
grow
th
dicot
photoreversibility
Pfr Prphotoactivation
Embryo
phytochromered and white light stimulate germination
cotyledons
1. Utilization of stored reserves– In cotyledons or endosperm tissue– During germination, enzymes are made that convert
stored reserves (large molecules) into compounds that can be used by the seedling (smaller molecules)
starches sugarslipids, fats sugarsproteins amino acids
Germination of seeds
GerminationGermination of of seedsseeds2. Transport of compounds into growing seedling through
vascular system– These compounds have two functions
Support respiration in the embryoProvide a source of building blocks (carbon, nitrogen, etc.) for
the seedling
3. Expansion and growth of seedling– Root radicle elongates down, hypocotyl expands up– Establishment of root system and emergence of shoot
Seedling establishmentSeedling establishment
Shoot emerges and is exposed to lightChlorophyll is produced and seedling starts to
perform photosynthesisSeedling is no longer dependent on reserves
from the seedIf stored reserves are consumed before
photosynthesis is established, the seedling will die
Seedling establishmentSeedling establishmentGrowth of the seedling can be measured in many
ways– Length
Increases after seed imbibes– Fresh weight
Increases as seedling grows– Dry weight
Declines initially as stored reserves are consumed by respiration, increases once photosynthesis is established
ConclusionsConclusionsSeeds are alive but dormantComprise an embryonic plant and stored
reservesGermination requires
– Water - for imbibition– Oxygen - for respiration– Suitable temperature
Outcome of successful germination is a seedling capable of independent growth
TYPES GERMINATIONTYPES GERMINATION
• Radicle will emerge first from the seedRadicle will emerge first from the seed• Next, the shoot tip breaks through the soil surfaceNext, the shoot tip breaks through the soil surface
• Types of germination:Types of germination:i.i. epigealepigeal
- cotyledons appear above the ground- cotyledons appear above the ground { hypocotyl forms a hook and pushes aboveground, raising { hypocotyl forms a hook and pushes aboveground, raising the the
cotyledons }cotyledons }
ii.ii. hypogealhypogeal- cotyledons remain underground- cotyledons remain underground { epicotyl forms a hook and shoot tip is lifted out of the soil }{ epicotyl forms a hook and shoot tip is lifted out of the soil }
……TYPES GERMINATIONTYPES GERMINATION
……TYPES GERMINATIONTYPES GERMINATION
Aggregate fruits
Receptacle is the fruit