6.4.2: Clones in plants Flashcards
What is the easiest way to create clones?
- Through making cuttings.
- A stem is cut between two leaf joints (nodes)
- The cut end of the stem is then placed into moist soil.
- New roots will grow from the tissues in the stem, usually from the node, but they may grow from the other parts of the burried stem.
What could help to encourage plants to take root more easily?
- Dipping the cut stem in rooting hormone which stimulates root growth.
- Wounding or removing bark from the cut end of the stem, as this encourages the plant to produce a callus.
Cuttings can also be made successfully from other parts of a plant:
- Root cuttings, in which a section of the root is burried just below the soil surface, and produces new shoots.
- Scion cuttings, which are doromant woody twigs.
- Leaf cuttings, in which a leaf is placed in moist soil. The leaves develop new stems and new roots. Some leaves may produce many new plants from one cutting
Why are many commercially grown houseplants coned using tissue culture techniques rather than cloning by taking cuttings?
- Large-scale cloning by taking cuttings can be time-consuming and needs a lot of space.
- Also, some plants do not respond well to takig cuttings.
What is tissue culture?
- A series of techniques used to grow cells, tissues or organs from a small sample of cells or tissue.
- It is carried out on a nutrient medium under sterile conditiond.
- Application of a growth substance at the correct time can encourage the cells in the growing tissue to differentiate.
What is micropropagation?
-Taking small pieces of plant tissue (the explant) and using plant growth substances to encourage it to grow and develop into a whole new plant.
There are 6 stages to micropropagation
Step 1:
suitable plant material selected and cut into small pieces. These are called explants. Explants could be pieces of leaf, stem, root or bud. Merisem tissue often used as it is always free from virus infection.
There are 6 stages to micropropagation
Step 1: suitable plant material selected and cut into small pieces. These are called explants. Explants could be pieces of leaf, stem, root or bud. Merisem tissue often used as it is always free from virus infection.
Step 2:
The explants are sterilised using dilute bleach or alcohol. This is essential to kill any bacteria and fungi, as these would thrive in the conditions supplied to help the plant grow well.
There are 6 stages to micropropagation
Step 2: The explants sre sterilised using dilute bleach or alcohol. This is essential to kill ant bacteria and fungi, as these would thrive in the conditions supplied to help the plant grow well.
Step 3:
The explants are placed on a sterile growth medium (usually agar gel) containing suitable nutrients such as glucose, amino acids and phosphates. The gel also contains high concentrations of the plant growth substances auxin and cytokinin. This stimulates the cells of each explant to divide by mitosis to form a callus (mass of undifferentiated totipotent cells)
There are 6 stages to micropropagation
Step 3: The explants are placed on a sterile growth medium (usually agar gel) containing suitable nutrients such as glucose, amino acids and phosphates. The gel also contains high concentrations of the plant growth substances auxin and cytokinin. This stimulates the cells of each explant to divide by mitosis to form a callus (mass of undifferentiated totipotent cells)
Step 4:
Once a callus has formed, it is divided to produce a larger number of small clumps of undifferentiated cells.
There are 6 stages to micropropagation
Step 4: Once a callus has formed, it is divided to produce a larger number if small clumps of undifferentiated cells.
Step 5:
These small clumps of cells are stimulated to grow, divide and differentiate into different plant tissues. This is achieved by moving the cells to different growth media. Each medium contains different ratios of auxin and cytokinin. The first medium contains the ratio 100 auxin: 1 cytokinin, and this stimulates roots to form. The second media contains the ratio 4 auxin: 1 cytokinin, which stimulates the shoots to form.
There are 6 stages to micropropagation
Step 5: These small clumps of cells are stimulated to grow, divide and differentiate into different plant tissues. This is achieved by moving the cells to different frowth media. Each medium contains different ratios of auxin and cytokinin. The first medium contains the ratio 100 auxin: 1 cytokinin, and this stimulates roots to form. The second media contains the ratio 4 auxin: 1 cytokinin, which stimulates the shoots to form.
Step 6:
Once tiny plantlets have been formed, these are transferred to a geenhouse to be grown in compost or soil and acclimatised to normal growing conditions.
What are the advantsages of artificial cloning?
- Quicker than producing plants from seed.
- Clan be carried out when sexual reproduction is not possible e.g. plants that have lost their ability to breed sexually (bananas).
- Plants that are difficult to grow from seed can be reproduced e.g. orchids for the horticultural industry.
- Plants selected will be genetically identical to the parent plant. They will have the desirable characteristics.
- If the original plat had an unusual combination of characteristics due to selective breeding or genetic modification, this characteristic can be retained without the risk of losing the combination through sexual reproduction.
- New plants are are all uniform in their phenotype which makes them easier to grow and harvest.
- Using the apical bud (meristem) as an explant for tissue culture ensures the new plants are free from viruses.
What are the disadvantages to artificial cloning?
- Tissue culture is labour intensive.
- Expensive to set up facilities to perform tissue culture successfully.
- Tissue culture can fail due to microbial contamination.
- All cloned offspring are genetically identical and are therefore susceptible to the same pests/diseases.
- No genetic variation, except that introduced by mutation.
