Transcript Artificial Clones in Plants

Artificial Clones in Plants
• Many horticultural cultivars (cultivated
varieties) are clones derived from single
individuals and propagated artificially:
– Grapes like Black Hamburg
– Potatoes like King Edwards, Santé, Desiré, Jersey
Royals to name but a few
– Bananas
– Apples like Bramley, Cox’s orange pippin,
Worcester permain, Egremont russet
• It is generally easy to propagate plants
asexually, though some are easier than others.
– The geranium and spider plants are ridiculously
easy.
• Common propagation methods are:
– Cuttings
– Grafts
Cuttings
• With stem cuttings, a stem is cut below a node and the
lower leaves are removed.
– This reduces water loss and so prevents undue stress for
the cutting.
• The stem is placed into gritty compost.
– Dip in hormone rooting powder
– Often the synthetic auxin naphthalene acetic acid (NAA)
• It is not transported away from the application site
• So exerts its rooting effect for longer
• Cuttings of gooseberry, currants and vines easily ‘strike’
or produce roots if they are taken in the autumn and
simply placed in soil.
Cutting of tomato plant:
• Stem cutting normally
placed in compost but
here simply placed in
water and left
• After a few days roots
appear
Grafts
• Pieces of plant material with a bud are grafted onto a
root stock.
• Grafted material might be:
– A shoot section with a terminal bud
• Placed into a V-shaped slit in the root stock
– A side bud
• Placed into a T-shaped slit in the bark of the root stock
• The root stock might be:
– ‘Wild’
• Provides vigour to the graft
– Dwarf so the grafted portion does not grow too tall
• Makes harvest easier
Scion or graft with
buds which can
grow once the graft
has taken
Root stock with Vshaped slit to
accept the graft
Scion or graft with a
bud which can grow
once the graft has
taken
Root stock with Tshaped slit in the
bark to accept the
graft
Cordon
apples
grafted onto dwarfing
rootstocks
Detail
of trained
the union
of a cordon-trained
apple grafted
onto a dwarfing rootstock
If you look near the base of a tree the graft
‘scar’ will often be evident
Apples and roses
readily produce viable
seed.
Why are they
generally propagated
by grafting?
• Sexual reproduction introduces
variation
– Meiosis
• Cross-over and independent
segregation
Apples from a tree grown from a pip
taken from a Katy apple. They share
some of the original characteristics
but they are not identical.
– Random fusion of male and
female gametes
• Seedlings give rise to plants that
are genetically different to
parent, so fruit is different
• Grafted plants
– Fruit identical, quicker to fruit,
root stock can dwarf plant
Artificial Propagation – Tissue Culture
• Tissue culture can be used to produce large
amounts of genetically identical plants from
small amounts of plant material.
• It has widespread horticultural and
conservation applications:
Horticultural
Conservation
 Production of large
numbers of plants, all
with required
characteristics
 Quickly and cheaply
 Production of large
numbers of endangered
plants
 Remove incentive to
collect from the wild
Horticultural Applications
• Where would keen gardeners and plant
lovers be without plug pots, miniature
roses and Phalaenopsis orchids?
Conservation Applications
• Large numbers of plants can be cloned from
endangered species
– Flood the market with cheap plants
– Little incentive for ‘poachers’ to collect material from the
wild (e.g. cycads)
• Alternatively, cloned plants can be used to restock
– An English elm reintroduction began in March 2010
– Micropropagation techniques used by the Conservation
Foundation to produce clones of surviving elms
• Read about the Great British Elm Experiment at
http://www.conservationfoundation.co.uk/project_info.php?id=2
Meristem Culture
• Meristematic tissue is capable of cell division
– Found in buds and in the cambium
• If buds are excised, they can be grown into
plantlets
– Meristematic tissue is largely virus free
– So cloned plants should be disease free
– Useful for cleaning diseased stock like potatoes
and soft fruit like strawberries
• The excised buds are surface sterilised
– Dip into disinfectant for a few seconds
• Place into a nutrient medium where
– They produce roots and grow
• It is really like taking cuttings, but on a micro
scale
• More buds can be taken from the plantlets
– Sub-culture
– Produce large numbers of identical plants
Callus Culture
• Meristematic tissue is removed from a donor
plant and surface sterilised.
• The explant is then placed onto a nutrient growth
medium.
– Meristematic cells divide
– Produce a mass of undifferentiated cells
– Wound or callus tissue
• The callus can be divided up and be transferred
onto fresh medium for further growth and
bulking up.
• Alternatively clumps of callus can be
transferred to medium with an appropriate
mix of hormones
– Stimulate differentiation of the callus into roots
and shoots
• Auxin to stimulate root formation
• Cytokinin to stimulate shoot formation
• Finally, the plantlets are transferred to fresh
medium in a greenhouse for growing on into
miniature plants.
Cell Culture
• Cells from callus culture can be transferred into a
liquid medium in a bioreactor.
– Can produce a range of useful plant metabolites
– Red dye shikonin is produced by Lithospermum
erythrorhizon
• High value and is produced in large amounts as a secondary
metabolite when cultured
– Shikonin also has medicinal uses
• e.g. it is a component of Chinese herbal medicine, is antiinflammatory, has anti-tumour properties, promotes wound
healing and inhibits HIV
– Shikonin was the first plant secondary metabolite to
be produced by cell culture.
Apical bud removed and surface sterilised
Apical bud placed onto nutrient
medium and incubated. It grows
and produces a rooted plantlet.
Explant surface sterilised,
produces callus in culture
Callus differentiates
with hormone
treatment
Rooted plantlets
grown on
Callus put into
cell suspension
culture
Plants for sale or planting
to restock in the wild
Pros and Cons of Cloning Plants in
Agriculture
• Discuss the potential advantages and
disadvantages of cloning plants in agriculture,
and then complete the summary table.
• You should consider:
–
–
–
–
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Cost
Genetic uniformity
Desirable qualities (e.g. good flowers, fruit or yield)
Ability to produce plants in sufficient numbers
Specific examples of potential benefit (e.g. producing
disease-free material, production of genetically
modified plants)
Advantages of Plant Cloning
Identical so have the desired
characteristics present in the
parent plant, e.g. crop with high
yield, taste, nutrient quality,
harvest at the same time.
Large numbers of identical
plants can be produced quickly
and cheaply.
Can be used with plants that
are incapable of normal sexual
reproduction, e.g. banana plant
is sterile (triploid).
Can be used with transgenic or
GM plants. Meristematic tissue
generally disease free.
Disadvantages of Plant Cloning
Genetically uniformity may
make them susceptible to
disease, e.g. English elm and
Dutch elm disease, potato
blight.
Labour intensive and trained
staff needed for tissue culture
and micropropagation.
Aseptic conditions needed for
micropropagation.
Single clones, so could
propagate genetic disease or
transfer pathogen if stock
contaminated.