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Seeds and Seed Seeds and Seed Germination Germination

Seeds and Seed Germination. Seeds and seed germination Seeds are normally the product of sexual reproduction Pollination Fertilization Embryo development

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Page 1: Seeds and Seed Germination. Seeds and seed germination Seeds are normally the product of sexual reproduction Pollination Fertilization Embryo development

Seeds and Seed GerminationSeeds and Seed Germination

Page 2: Seeds and Seed Germination. Seeds and seed germination Seeds are normally the product of sexual reproduction Pollination Fertilization Embryo development

Seeds and seed germinationSeeds and seed germination

Seeds are normally the product of sexual reproduction

Pollination

Fertilization

Embryo development

Mature seed

Page 3: Seeds and Seed Germination. Seeds and seed germination Seeds are normally the product of sexual reproduction Pollination Fertilization Embryo development

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?

Page 4: Seeds and Seed Germination. Seeds and seed germination Seeds are normally the product of sexual reproduction Pollination Fertilization Embryo development

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

Page 5: Seeds and Seed Germination. Seeds and seed germination Seeds are normally the product of sexual reproduction Pollination Fertilization Embryo development

Diversity among seedsDiversity among seeds

In terms of adaptation to survive various environments until conditions are favorable for germination

In terms of method of dispersal

Page 6: Seeds and Seed Germination. Seeds and seed germination Seeds are normally the product of sexual reproduction Pollination Fertilization Embryo development

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

Page 7: Seeds and Seed Germination. Seeds and seed germination Seeds are normally the product of sexual reproduction Pollination Fertilization Embryo development

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?

Page 8: Seeds and Seed Germination. Seeds and seed germination Seeds are normally the product of sexual reproduction Pollination Fertilization Embryo development

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

Page 9: Seeds and Seed Germination. Seeds and seed germination Seeds are normally the product of sexual reproduction Pollination Fertilization Embryo development

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

Page 10: Seeds and Seed Germination. Seeds and seed germination Seeds are normally the product of sexual reproduction Pollination Fertilization Embryo development

Monocots and DicotsMonocots and Dicots

Flowering 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

Page 11: Seeds and Seed Germination. Seeds and seed germination Seeds are normally the product of sexual reproduction Pollination Fertilization Embryo development

Seed structureSeed structure

Cotyledon

Plumule

Radicle

Micropyle

Seed coat or testa

Page 12: Seeds and Seed Germination. Seeds and seed germination Seeds are normally the product of sexual reproduction Pollination Fertilization Embryo development

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.

Page 13: Seeds and Seed Germination. Seeds and seed germination Seeds are normally the product of sexual reproduction Pollination Fertilization Embryo development

Endospermous or non-Endospermous or non-Endospermous seeds?Endospermous seeds?

Page 14: Seeds and Seed Germination. Seeds and seed germination Seeds are normally the product of sexual reproduction Pollination Fertilization Embryo development

Endospermous and non-Endospermous and non-Endospermous seedsEndospermous seeds

A LS of maize grain / fruitA LS of maize grain / fruit

Page 15: Seeds and Seed Germination. Seeds and seed germination Seeds are normally the product of sexual reproduction Pollination Fertilization Embryo development

• 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 oxygen

ii. Dryness

iii. Presence of substances that inhibit germination

SEED DORMANCYSEED DORMANCY

Page 16: Seeds and Seed Germination. Seeds and seed germination Seeds are normally the product of sexual reproduction Pollination Fertilization Embryo development

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

Page 17: Seeds and Seed Germination. Seeds and seed germination Seeds are normally the product of sexual reproduction Pollination Fertilization Embryo development

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 _____ _____ _____

Page 18: Seeds and Seed Germination. Seeds and seed germination Seeds are normally the product of sexual reproduction Pollination Fertilization Embryo development

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

Page 19: Seeds and Seed Germination. Seeds and seed germination Seeds are normally the product of sexual reproduction Pollination Fertilization Embryo development
Page 20: Seeds and Seed Germination. Seeds and seed germination Seeds are normally the product of sexual reproduction Pollination Fertilization Embryo development

CHAPTER : GROWTH

SEED GerminationSEED Germination

Dormancy 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.

Page 21: Seeds and Seed Germination. Seeds and seed germination Seeds are normally the product of sexual reproduction Pollination Fertilization Embryo development

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

Page 22: Seeds and Seed Germination. Seeds and seed germination Seeds are normally the product of sexual reproduction Pollination Fertilization Embryo development

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

Page 23: Seeds and Seed Germination. Seeds and seed germination Seeds are normally the product of sexual reproduction Pollination Fertilization Embryo development

Maintaining dormancyMaintaining dormancy

Physical 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

Page 24: Seeds and Seed Germination. Seeds and seed germination Seeds are normally the product of sexual reproduction Pollination Fertilization Embryo development

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

Page 25: Seeds and Seed Germination. Seeds and seed germination Seeds are normally the product of sexual reproduction Pollination Fertilization Embryo development

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

Page 26: Seeds and Seed Germination. Seeds and seed germination Seeds are normally the product of sexual reproduction Pollination Fertilization Embryo development

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.

Page 27: Seeds and Seed Germination. Seeds and seed germination Seeds are normally the product of sexual reproduction Pollination Fertilization Embryo development

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/

Page 28: Seeds and Seed Germination. Seeds and seed germination Seeds are normally the product of sexual reproduction Pollination Fertilization Embryo development

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)

Page 29: Seeds and Seed Germination. Seeds and seed germination Seeds are normally the product of sexual reproduction Pollination Fertilization Embryo development

The control of food reserve The control of food reserve hydrolysishydrolysis

Negative feedback control of enzymes

The action of the enzyme also limited by substrate

Once all the starch in an amyloplast is hydrolysed the enzyme stops work

Therefore the release of the stored food is adjusted to suite the demand

Starch + H20 Maltose - amylase

Negative feedback

Page 30: Seeds and Seed Germination. Seeds and seed germination Seeds are normally the product of sexual reproduction Pollination Fertilization Embryo development

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

Page 31: Seeds and Seed Germination. Seeds and seed germination Seeds are normally the product of sexual reproduction Pollination Fertilization Embryo development

GAABAABAABA

Light, chilling or

water (rain) trigger the

inactivation of ABA, which

makes dormant

seeds able to germinate.

Triggering factors for germination

Page 32: Seeds and Seed Germination. Seeds and seed germination Seeds are normally the product of sexual reproduction Pollination Fertilization Embryo development

GA

After seeds take up water, GA is released from the embryo to signal aleurone.

Page 33: Seeds and Seed Germination. Seeds and seed germination Seeds are normally the product of sexual reproduction Pollination Fertilization Embryo development

-amylase

The aleurone responds by synthesizing and secreting digestive enzymes (-amylase) to hydrolyze stored

nutrients in the endosperm.

Page 34: Seeds and Seed Germination. Seeds and seed germination Seeds are normally the product of sexual reproduction Pollination Fertilization Embryo development

Nutrients (ex. sugars) absorbed from the endosperm by the scutellum (cotyledon) are

consumed by the seedling during germination.

Page 35: Seeds and Seed Germination. Seeds and seed germination Seeds are normally the product of sexual reproduction Pollination Fertilization Embryo development

The growth of seedling starting with the roots first, then shoot growth follows.

Page 36: Seeds and Seed Germination. Seeds and seed germination Seeds are normally the product of sexual reproduction Pollination Fertilization Embryo development

Barley Seed Germination

Fruit+Seed Coat

Endosperm

Aleurone LayerStorage Protein

Amino Acids

hydr

olys

is

tran

slat

ion

trans

crip

tion

hydro

lysis

starch

sugar

-amylase

RNA

DNA GA

imbibition

water

radicle apex

shoot apex

grow

th

cotyledon

monocot

maltose

Embryo

exocytosis

Page 37: Seeds and Seed Germination. Seeds and seed germination Seeds are normally the product of sexual reproduction Pollination Fertilization Embryo development

Capsella Seed:

Seed Coat

Endosperm

Embryo

Shoot Apex

Cotyledons - dicot

Hypocotyl

Radicle

Root Apex

Micropyle

Page 38: Seeds and Seed Germination. Seeds and seed germination Seeds are normally the product of sexual reproduction Pollination Fertilization Embryo development

Lettuce Seed Germination

660 nm

730 nm

dark

Seed Coat

trans

latio

n

trans

crip

tion

hydrolysisstarch

sugar

-amylase

RNA

DNA

imbibition

water

radicle apex

shoot apex

grow

th

dicot

photoreversibility

Pfr Prphotoactivation

Embryo

phytochromered and white light stimulate germination

cotyledons

Page 39: Seeds and Seed Germination. Seeds and seed germination Seeds are normally the product of sexual reproduction Pollination Fertilization Embryo development

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

Page 40: Seeds and Seed Germination. Seeds and seed germination Seeds are normally the product of sexual reproduction Pollination Fertilization Embryo development

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

Page 41: Seeds and Seed Germination. Seeds and seed germination Seeds are normally the product of sexual reproduction Pollination Fertilization Embryo development
Page 42: Seeds and Seed Germination. Seeds and seed germination Seeds are normally the product of sexual reproduction Pollination Fertilization Embryo development

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

Page 43: Seeds and Seed Germination. Seeds and seed germination Seeds are normally the product of sexual reproduction Pollination Fertilization Embryo development

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

Page 44: Seeds and Seed Germination. Seeds and seed germination Seeds are normally the product of sexual reproduction Pollination Fertilization Embryo development

ConclusionsConclusions

Seeds 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

Page 45: Seeds and Seed Germination. Seeds and seed germination Seeds are normally the product of sexual reproduction Pollination Fertilization Embryo development
Page 46: Seeds and Seed Germination. Seeds and seed germination Seeds are normally the product of sexual reproduction Pollination Fertilization Embryo development

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 }

Page 47: Seeds and Seed Germination. Seeds and seed germination Seeds are normally the product of sexual reproduction Pollination Fertilization Embryo development

……TYPES GERMINATIONTYPES GERMINATION

Page 48: Seeds and Seed Germination. Seeds and seed germination Seeds are normally the product of sexual reproduction Pollination Fertilization Embryo development

……TYPES GERMINATIONTYPES GERMINATION

Page 49: Seeds and Seed Germination. Seeds and seed germination Seeds are normally the product of sexual reproduction Pollination Fertilization Embryo development
Page 50: Seeds and Seed Germination. Seeds and seed germination Seeds are normally the product of sexual reproduction Pollination Fertilization Embryo development
Page 51: Seeds and Seed Germination. Seeds and seed germination Seeds are normally the product of sexual reproduction Pollination Fertilization Embryo development
Page 52: Seeds and Seed Germination. Seeds and seed germination Seeds are normally the product of sexual reproduction Pollination Fertilization Embryo development
Page 53: Seeds and Seed Germination. Seeds and seed germination Seeds are normally the product of sexual reproduction Pollination Fertilization Embryo development

Aggregate fruits

Page 54: Seeds and Seed Germination. Seeds and seed germination Seeds are normally the product of sexual reproduction Pollination Fertilization Embryo development
Page 55: Seeds and Seed Germination. Seeds and seed germination Seeds are normally the product of sexual reproduction Pollination Fertilization Embryo development
Page 56: Seeds and Seed Germination. Seeds and seed germination Seeds are normally the product of sexual reproduction Pollination Fertilization Embryo development

Receptacle is the fruit

Page 57: Seeds and Seed Germination. Seeds and seed germination Seeds are normally the product of sexual reproduction Pollination Fertilization Embryo development