M6, C22 Cloning and Biotechnology

Question 1

where can new plants propagate from

Answer 1

stem
leaf
buds
root

Question 2

Where does natural plant cloning / vegetative propogation occur?

Answer 2

Bulbs - leaf bases swell with stored food from photosynthesis. Buds form internally which develop into new shoots.

Runners - a lateral stem grows away from the parent plant and roots develop where the runners hit the ground.

Rhizomes - a specialised horizontal stem running underground, often swollen with stored food. Buds develop and form new vertical shoots which become independent plants.

Stem tubers - the tip of an underground stem becomes swollen with stored food to form a tuber or storage organ. Buds develop to produce new shoots.

Question 3

What are the advantages and disadvantages of using cuttings

Answer 3

faster than using seeds
guarantees quality of the plant
offspring are genetically identical

lack of genetic variation - disease or climate change could wipe them all out

Question 4

How do you produce a clone from a cutting

Answer 4

1) Use a scalpel to cut a piece of stem from the parent plants between 5 and 10 cm.
2) Remove the leaves from the lower end of your cutting, leaving one at the tip.
3) Dip the lower end of the cutting in rooting powder, which contains hormones that induce root formation.
4) Then plants your cutting in a pot containing well-drained compost.
5) Provide your cutting with a warm and moist environment by covering in a plastic bag or putting in propagator.
6) When your cutting has formed its own roots and is strong enough, plant it elsewhere to continue growing.

Question 5

define micropropagation

Answer 5

the process of making large numbers of genetically identical offspring from a single parent plant using tissue cultures techniques

Question 6

when is micropropagation used

Answer 6

When the desirable plant…

• doesn’t readily produce seeds
• doesn’t respond well to natural cloning
• is very rare
• has been genetically modified or selectively bred with difficulty
• is required to be ‘pathogen-free’ by growers

Question 7

what is the process of micropropagation using tissue culture

Answer 7

1) Take a small sample of tissue from the plant you want to clone. (The meristem tissue from shoot tips and axial buds is often dissected out in sterile conditions to avoid contamination by fungi and bacteria. Usually virus free).
2) Sterilise the sample by immersing in sterilising agents. The latter isn’t rinsed off. The material removed is called the explant.
3) The explant is placed in a sterile culture medium containing a balance of plant hormones (auxins and cytokinins) which stimulate mitosis. The cells multiply, forming a mass of identical cells called a callus.
4) The callus is divided up and individual cells or clumps from the callus are transferred to a new culture medium containing a different mixture of hormones and nutrients which stimulates the development of plantlets.
5) The plantlets are potted into compost where they grow into small plants.
6) The young plants are planted out to grow and produce a crop.

Question 8

What are the reasons for micropropagation?

Answer 8

• Allows for the rapid production of large numbers of plants which will yield good crops.
• Culturing meristem tissue produces disease-free plants.
• Makes it possible to produce viable numbers of plants after genetic modification of plant cells.
• Provides a way of producing very large numbers of new plants which are seedless and meets consumer tastes.
• Provides a way of growing plants which are naturally relatively infertile or difficult to grow from seed.
• Provides a way of reliably increasing the numbers of rare or endangered plants.

Question 9

what are the reasons against micropropagation?

Answer 9

• produces a monoculture (many plants that are genetically identical) so all are susceptible to the same diseases or changes in growing conditions.
• relatively expensive process and requires skilled workers.
• the explants and plantlets are vulnerable to infection
• if the source material is infected with a virus, all clones will also be infected.
• in some cases, large numbers of new plants are lost during the process

Question 10

Give some different ways vegetative propagation is used in horticulture

Answer 10

1) Cuttings
2) Grafting - joining the shoot of one plant to the stem and root of another
3) Layering - bending a stem of a growing plant downwards so it enters the soil an grows a new plant
4) Split up bulbs
5) Remove young plants from runners
6) Cut up rhizomes (horizontal roots grown underground which produce own shoots)