1. Seeds and Seed Germination

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

3. Seeds are for propagation
The biological function of seeds is for propagation of the species
How does seeds help in propagation of the species?

4. Diversity among seeds Seeds are very diverse in term of size:
Begonia seed weigh micrograms
Coconuts weigh more than a kilogram
Thousands of Begonia seeds

5. Diversity among seeds
In terms of adaptation to survive various environments until conditions are favorable for germination In terms of method of dispersal

6. Seeds are for propagation
Protect the zygote against physically injury
Store foods for seedling-- before it becomes independent
Remain dormant to survive harsh environment
Disperse the seeds to capitalize on their genetic variability
Respond to environment cues and germinate at the right time and place

7. Seeds are alive! To function in propagation, seeds must be alive
Seeds respire, albeit slowly
consume O2, produce CO2 and H2O
Seeds have a finite lifespan
they cannot be stored indefinitely
Which kind of seeds can remain viable longer? Seeds of tropical plant or temperate plant?

8. 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

9. General 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

10. Monocots and Dicots Flowering plants (angiosperms):
Dicotyledonous plants with two seed leaves
Monocotyledonous plants with one seed leaf
Dicots
200,000 species
includes beans, roses, cacti, melons, citrus
Angiosperms
flowering plants
Monocots
50,000 species
includes grasses, lilies, orchids, palms

11. Seed structure
Cotyledon
Plumule
Radicle
Micropyle
Seed coat or testa

12. Endospermous and non- Endospermous 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.

13. Endospermous or non- Endospermous seeds?

14. A LS of maize grain / fruit
Endospermous and non- Endospermous seeds
A LS of maize grain / fruit

15. SEED DORMANCY
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:
Lack of oxygen
Dryness
Presence of substances that inhibit germination 15

16. GROWTH 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
CHAPTER : GROWTH 16

17. What physiological changes lead to dormancy
Metabolism falls
Number of organelles per cell _____
Dehydration – water content _____
Vacuoles in cells _____
Food reserves become _____ _____ _____

18. What physiological changes lead to dormancy
Metabolism falls
Number of organelles per cell falls
Dehydration – water content falls
Vacuoles in cells deflate
Food reserves become dense crystalline bodies 18

20. SEED Germination
Dormancy of these seeds may be broken by one or more of the following:
light, sunlight being the most effective;
low temperatures (1 to 5 degrees Celsius [33.8 to 41 degrees Fahrenheit]) for several weeks;
day/night fluctuating temperatures of 1 to 10 degrees Celsius (41 to 50 degrees Fahrenheit);
chemicals, such as nitrate in the soil, or applied hormones (gibberellins) in the laboratory; and
fire.
CHAPTER : GROWTH 20

21. Dormancy mechanism is related to the seeds’ natural environment
is particularly important for small, wind-dispersed weed seeds.
Seeds that require light involves a receptor protein, phytochrome
the cold winter may cause the parent plant to die, and thus remove competition for space in the spring.
Seeds that need a period of low temperature
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 21

22. Dormancy mechanism is related to the seeds’ natural environment
Seeds that require light involves a receptor protein, phytochrome
Seeds that need a period of low temperature
The requirement for alternating temperatures
The requirement for fire
CHAPTER : GROWTH 22

23. Maintaining dormancy
Physical barriers The seed coat (testa) is waxy = waterproof and impermeable to oxygen
Physical state – dehydrated
Chemical inhibitors present e.g. salts, mustard oils, organic acids, alkaloids
Growth promoters absent

24. The breaking of dormancy
Break down of barriers
Abrasion 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

25. Seed Germination: To break dormancy seeds need: Water Warm Temperature
Emergence of Radicle through Seed Coat
To break dormancy seeds need:
Water
Warm Temperature
So if you want to store seeds what are the conditions?
Dry Cold
Dormant seeds need more than moisture and warmth:
Dormancy is caused by:
Is overcome by:
Example:
nick digest
scrub fire
freeze-thaw cycles
Thick Seed Coat
Scarification
Kentucky Coffee Tree or
Thin Seed Coat
Light
Dark
Lettuce
Pea
Insufficient Development
Soil Fungus Association
Orchids
Inhibitor: Abscisic Acid
Stratification > Vernalization
Most CT feral plants
6 weeks at 4° C
20° C
Inhibitor: Phenolics
Leaching by Repeated Rain
Cacti

26. Germination STAGE EVENTS PREGERMINATION
Rehydration – imbibition of water.
RNA activated & protein synthesis starts.
Increased metabolism – increased respiration.
Hydrolysis (digestion) of food reserves by enzymes.
Induction of cell division & cell growth.
GERMINATION
Rupture of seed coat.
Emergence of seedling, usually radicle first.
POST GERMINATION
Growth of root and shoot axis. Transport of materials from food stores to growing axis.
Senescence (aging) of food storage tissues.

27. Stages leading to cell division
Respiration
Initially anaerobic
Later aerobic
Mitchondria reconstituted
Soluble sugars
ATP
RNA activated
Protein synthesis (0.5h)
Enzymes (proteins)
DNA synthesis (45h)
Mitosis (70h)

28. Mobilization of food reserves
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)

29. The control of food reserve hydrolysis
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

30. The mobilisation of food reserves
Carbohydrates
Starches (amylopectin & amylose)
Amylases
Maltose and glucose
Proteins
e.g. Zein
Proteases
Amino acids
Lipids
Oils
Lipases
Fatty acids & glycerol
The food reserves are stored as large insoluble macromolecules
They are hydrolysed using enzymes to smaller soluble molecules for transport

31. ABA Triggering factors for germination
Light, chilling or water (rain) trigger the inactivation of ABA, which makes dormant seeds able to germinate.
ABA
ABA
ABA GA

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

33. The aleurone responds by synthesizing and secreting digestive enzymes (a-amylase) to hydrolyze stored nutrients in the endosperm.
a-amylase

34. Nutrients (ex. sugars) absorbed from the endosperm by the scutellum (cotyledon) are consumed by the seedling during germination.

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

36. Barley Seed Germination
hydrolysis
starch
Fruit+Seed Coat
maltose
Endosperm
sugar
exocytosis
Aleurone Layer
cotyledon
-amylase
translation
Storage Protein
monocot
hydrolysis
shoot apex
RNA
growth
transcription
Embryo
Amino Acids
DNA GA
water
radicle apex
imbibition

37. Capsella Seed:
Embryo
Seed Coat
Shoot Apex
Endosperm
Cotyledons - dicot
Hypocotyl
Radicle
Root Apex
Micropyle

38. Lettuce Seed Germination
shoot apex
hydrolysis
starch
Seed Coat
sugar
cotyledons
-amylase
translation
dicot
growth
RNA
transcription
Embryo
DNA
photoactivation
phytochrome
radicle apex
photoreversibility
red and white light stimulate germination
water
660 nm
Pfr Pr
dark
730 nm
imbibition

39. Germination of seeds 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  sugars
lipids, fats  sugars
proteins  amino acids

40. Germination of seeds
2. Transport of compounds into growing seedling through vascular system
These compounds have two functions
Support respiration in the embryo
Provide 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

42. Seedling establishment
Shoot emerges and is exposed to light
Chlorophyll is produced and seedling starts to perform photosynthesis
Seedling is no longer dependent on reserves from the seed
If stored reserves are consumed before photosynthesis is established, the seedling will die

43. Seedling establishment
Growth 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

44. Conclusions Seeds are alive but dormant
Comprise an embryonic plant and stored reserves
Germination requires
Water - for imbibition
Oxygen - for respiration
Suitable temperature
Outcome of successful germination is a seedling capable of independent growth

46. TYPES GERMINATION Radicle will emerge first from the seed
Next, the shoot tip breaks through the soil surface
Types of germination:
i. epigeal
- cotyledons appear above the ground
{ hypocotyl forms a hook and pushes aboveground, raising the cotyledons }
ii. hypogeal
- cotyledons remain underground
{ epicotyl forms a hook and shoot tip is lifted out of the soil }

47. …TYPES GERMINATION

48. …TYPES GERMINATION

53. Aggregate fruits

56. Receptacle is the fruit