(1) Methods of cloning
plants
Reminders: A chromosome as a thread-like structure of
DNA, carrying genetic information in the form of genes.
A gene is a length of DNA that codes for a protein. An
allele as a version of a gene.
Reminder that in the biological
science of genetics, inheritance is the transmission of genetic
information from one generation to the next generation by chromosomes of
DNA.
Note that selective breeding
involves sexual reproduction, producing variable offspring -
genetically varied.
This means the offspring might
not inherit the desired characteristics you want.
Plant tissue culture produces
genetically identical offspring (clones)
of the parent plant - ensuring you know what their characteristics
will be.
Plant stem cells from meristems can be used to make
clones - so identical genetic copies of a plant can be grown quickly
and cheaply.
See
Hormone control of plant growth and uses of plant hormones
gcse biology revision notes
This means plant growers can grow
crops of identical plants that have been genetically engineered
to have more desirable features for farmers e.g. increased
size of wheat grain, more disease resistant - but GM crops are also a
controversial topic too!
Cloning has an important application
in preserving rare species of plants - to grow more of those in
danger of becoming extinct.
There are two ways of producing cloned plants.
1.1
Plant tissue culture technique
Tissue culture involves growing cells on, or
in, an artificial growth medium like an agar jelly or liquid broth.
This enables you to grow whole plants from the
cells of an individual plant - this can be done quickly, in
relatively little space and all year round.
Method
You first select tissue cells from a plant which has
the
desirable characteristics you are interested in to clone - it can be a GM plant
too.
They might be from a crop with good pesticide
resistance, a tasty fruit/vegetable, an attractive flower.
The best tissue cells are obtained from
fast-growing root or shoot tips - meristem tissues.
Here you put a few plant cells from the
meristems into a dish of an artificial growth medium (agar gel)
that contains nutrients and growth hormones including
auxins. The agar supports the tiny plants.
The growth should be under aseptic (sterile)
conditions to prevent growth of harmful microbes or fungus.
See
Hormone control of plant growth and uses of plant hormones
The auxins promote growth by promoting cell
division and cells grow quickly, elongating into new whole plants, all of
which are clones of the original parent plant.
As the tissues grow shoots and roots they can
be carefully be removed into potting compost and grown to full
maturity.
These cloned plants can be grown very quickly
using little space in a controlled nutrient medium and can be
cultured at any time of the year - seasons don't count anymore!
Remember these are clones - genetically
identical plants.
This tissue culture technique is used by or
for:
(i) biology scientists (botanists in this
case) to preserve rare plants in danger of extinction that are difficult to reproduce
naturally - especially important now that many habitats are
under threat from human activity in the landscape and
unfavourable climate changes.
(ii) Horticulturalists can produce lots of
stock of plants in their nurseries very efficiently and quickly.
(iii) You can use tissue culture to create
genetically identical lines of plants with beneficial traits
e.g. fruit taste, fruit yield, pesticide resistance - but these
are NOT genetic modifications.
See also
Hormone control of plant growth and uses of plant hormones
1.2
Using cuttings from plants
This is a traditional older method, and
simpler to apply than the tissue culture described above.
Many experienced gardeners take cuttings
(small sections of tissue) from
good healthy parent plants and then plant the cuttings in compost
containing hormones to
produce genetically identical copies of the parent plants.
Method
The best tissue for this technique is
obtained by slicing cuttings from fast-growing root or shoot tips (meristems
tissues) or a cutting with
a bud on it.
But it can be just a
leaf and stem
dipped in hormone powder to encourage rooting.
The cutting then grows into a new plant in
composting material.
Hormone rooting powders are used to
promote growth and they contain synthetic auxin hormones like
NAA which promotes growth of new roots from the cutting.
See also
Hormone control of plant growth and uses of plant hormones
The samples should be kept in moist
conditions until ready for use.
Again, these plants can be produced quickly
and cheaply both by professional or amateur gardeners.
1.3
Cloning using genetic engineering
e.g. using the genetic modification of plant cells
using a bacterium, then cloning the plant cells to produce a
commercially viable plant - all described in the diagram above!
Cloning of GM plant cells
for desired characteristic is described in
more detail
in another section
Important note on cloning:
After plant or animal cells have been
genetically modified, it is essential that they transfer the
newly introduced genes.
Cells are first screened e.g. with an
antibiotic, to kill cells that do not have the inserted gene.
The cells can then be successfully cloned
and collected for use.
Key points -
Summary of ideas
and other methods specifically about cloning plants
Based on
the syllabus-specifications for students taking the AQA, Edexcel and OCR
GCSE level biology examinations (~US grades 9-10).
Cloning plants is an important technique in agriculture
and horticulture, allowing for the reproduction of genetically identical
plants with desirable traits. Here are the main methods:
1.
Tissue Culture (Micropropagation)
This method involves growing new plants from small
sections of a parent plant, called explants. These are
placed in a sterile nutrient-rich agar medium containing plant
hormones to stimulate growth.
Tissue culture is useful for producing large numbers of
identical plants quickly and preserving rare species.
2.
Plant Cuttings
A simple and widely used method where a branch
or stem is cut from the parent plant, its lower leaves are
removed, and it is planted in damp compost.
Rooting hormones
may be applied to encourage root development.
This technique is commonly used by gardeners and
farmers.
3.
Genetic Engineering & Cloning
Genetic engineering allows scientists to modify plant
DNA to introduce desirable traits, such as disease resistance
or higher yield.
Once modified, the plant can be cloned
using tissue culture or other methods to produce genetically identical
copies.
4.
Grafting
A method where a cutting (scion) from
one plant is attached to the rootstock of another. This
is commonly used in fruit trees to combine the best traits of two
plants.
5.
Bulbs, Runners, and Tubers
Some plants naturally clone themselves through
structures like bulbs (onions), runners (strawberries), and
tubers (potatoes).
These grow into genetically identical
offspring.
Note that each method has advantages depending on the
plant species and purpose.
Tissue culture is ideal for large-scale production, while
cuttings and grafting are simpler for home gardening.
Summary of learning objectives and key words or phrases
Be able to describe three different methods of cloning
plants using plant tissue culture, using plant cuttings, GM genetic
engineering for cloning plant cells to produce new identical plants.
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