Transcript Asexual Reproduction in Plants

Chapter 30
Asexual Reproduction
in Plants
Vegetative Propagation
1
Learning objectives
1. State that vegetative propagation is asexual
reproduction
2. Give 1 example of vegetative propagation
from stem, root, leaf, bud
3. Compare reproduction by seed and by
vegetative reproduction
4. Outline 4 methods of artificial propagation
in flowering plants
Asexual reproduction
1. involves only one parent,
2. does not involve seeds or the fusion of gametes
3. Instead part of a plant’s stem, leaves or roots
can become new plants,
4. Produces offspring / clones genetically identical
to the parent,
5. Allows plants to be produced much faster then
sexual reproduction.
3
Vegetative Propagation
• Is a form of asexual reproduction in plants,
1. Can happen naturally e.g. runners, tubers,
plantlets, bulbs
2. or it can be done artificially by growers.
4
Methods of Natural Propagation
MODIFIED PLANT FOOD STORAGE
ORGANS
5
1. Modified Stems
(a) Runners
• Horizontal stem which
grows or runs over the
soil surface.
• The terminal bud sends
up new shoots & down
new roots from it.
• e.g. strawberries
6
7
Creeping buttercup
8
(b) Stem Tubers
• The tips of these underground
stems become swollen with
stored food- starch.
• The swollen tips are called
tubers.
• The “eyes” are lateral buds
that produce new shoots and
roots using the stored food.
• E.g. Potatoes
9
10
2.
Modified Roots
Root Tubers
• fibrous roots which
swell with stored food
• the tubers break off &
grow into a new plant
e.g. dahlias
11
Tap Roots
e.g. carrot and
turnip, are swollen
roots for food
storage in plants,
storage in biennial
plants… they are
not reproductive
organs
12
3.
Modified Leaves
Plantlets
• Some plants produce
small plants on the side
of their leaves.
• When they reach a
certain size,they fall off
and grow into new
plants.
• e.g. cacti
13
4. Modified Buds
Bulbs
A bulb (an underground bud) has a reduced stem,
roots, fleshy leaves swollen with stored food and a
main bud in the centre which grows into a new plant
e.g. onion, daffodil, tulip
14
15
16
Vegetative propagation may form new plants from
the following structures:
1. stems, such as runners in strawberries
2. roots, such as root tubers in dahlias
3. leaves, in cacti
4. buds, in bulbs such as onions or daffodils
17
Comparison of reproduction by
seed (sexual) and by vegetative
propagation (asexual)
18
The advantages of seed (sexual)
reproduction are:
1. variation in offspring
2. more disease resistance
3. less overcrowding due to seed dispersal
4. dormant seeds survive in soil
Advantage to seed formation
Sexual (seed)
Asexual (vegetative)
Cross pollination ensures
variation (allows evolution)
No variations –
can be advantage in
commercial horticulture
More resistant to disease
All plants are of same species
susceptible to disease
Dispersal reduces competition
Overcrowding and competition
Seeds can remain dormant and No seeds formed –
survive unfavourable conditions no dormancy
20
The advantages of vegetative (asexual)
reproduction are:
1. it is a simple process
2. no external agents are needed
3. young plants show fast growth
4. there is little waste
Advantage to vegetative propagation
Sexual (seed)
Asexual (vegetative)
Complex process
Simple process
Depends on outside agents
for seed dispersal
No outside agents needed
Slow growth of young plants
to maturity
Rapid growth
Wasteful e.g. petals, pollen,
fruit
No waste
22
Vegetative propagation
Artificial methods used in agriculture &
horticulture to propagate / grow new
plants that are identical to the parent
23
1. Cuttings
• Parts of a plant (usually
shoots) that are removed
from the parent plant
• rooted in well-watered
compost, soil or rooting
powder &
• allowed to form into a new
plant
• e.g. busy lizzie, geranium
24
25
2. Grafting
• Involves fixing /
binding together the
cut surfaces of 2 plants
(similar) so they grow
as one.
• Useful qualities from
both plants combined
into one e.g. rose
flower and thorn-less
stem e.g. apple trees.
26
27
28
3. Layering
• A branch of a plant is bent over and pinned
down into the soil at a node.
• It is covered over with soil & eventually new
roots & shoots develop.
• Useful for the propagation of woody plants
e.g. blackberry, gooseberry.
29
30
Micro- propagation (Tissue Culture)
• Some cells are removed
from plant are placed in a
dish with nutrients &
growth regulators
• They grow into a group of
similar cells called a callus
• Which develops into a
small plant & then placed
into compost.
31
• Entire plants can be grown from a small
piece of stem, leaf or root tissue
• Used in mass production of house plants
and crops such as bananas and strawberries.
• Provides a larger number of plants more
quickly than cuttings
32
Micropropagation (Tissue Culture)
33
Artificial methods of vegetative propagation
include:
1. cuttings – shoots that are removed from a
plant and allowed to form new plants
2. grafting – a section from one plant is
attached to a section of another plant
3. layering – a branch of a plant is fixed into
the soil to allow it to form roots and a new
plant
4. micropropagation – the growth of new
plants from tiny pieces of a parent plant
Cloning
• All offspring genetically identical - produced
asexually
• Clones are produced by mitosis
• All the offspring from the various methods
of vegetative reproduction (both natural
and artificial) mentioned are examples of
clones.
35
Dolly the clone
36
• Since 1996, when pioneering Scots cloned Dolly
the sheep from an adult sheep cell, scientists
have cloned mice, cows, goats, pigs, rabbits, cats,
rats, deer, mules, horses, and dogs.
• Yet despite all the success, cloning remains really,
really hard to do.
• Nature makes clones--genetic duplicates--all the
time. We call them identical twins. But twins
grow according to the DNA code from embryonic
stem cells--cells that are supposed to divide and
grow into complete adult beings.
• Cloners try to get the DNA from adult cells to do
the same thing.
37
Advantages of Cloning
Potential benefits to modern medicine –
1. cells can be manipulated to mimic other types of
cells, new ways to treat diseases like cancer and
Alzheimer’s.
2. Cloning also offers hope to persons needing
organ transplants - producing more animals that
can act as suitable donors. Pig livers have been
successfully transplanted to human beings.
38
Disadvantages of Cloning
1. The Element of Uncertainty- in the cause of
Dolly, many embryos were destroyed - 277 eggs
before the desired result was achieved.
2. Inheriting diseases - Cloning creates a copy of
the original. A human clone would therefore
inherit the genetic traits of its predecessor.
3. The Potential for Abuse - clones could be grown
in a farm-like fashion simply for harvesting
organs or stem cells, devalue human life ????
39
END
40
Definition
Asexual reproduction
• does not involve the manufacture or union of sex
cells or gametes e.g. binary fission, fragmentation,
spore formation and budding
• It involves only one parent and offspring are
genetically identical (have the same genetic
content) to the parent
41