Cloning in plants
There are two main types of cloning in plants: natural cloning and artificial cloning. In both cases, the offspring are genetically identical to the parent plant.
Natural cloning
Stem tubers - An underground storage organ. Contains buds that divide by mitosis to form more genetically identical tubers. Tubers are storage organs that store starch. An example of a tuber is a potato.
Bulbs - Another type of storage organ, so also another store of starch. Formed from swollen leaves. The buds are internal and grow into roots or shoots depending on their position in the plant.
Runners - Lateral stems that grow from the parent plant that form roots when they touch the ground and develop into new plants. New plants can be cut off the runner stem and potted so that they can grow separately from the main plant.
Artificial cloning
Cuttings - The plant stem is cut at an angle between the nodes. It is important that a stem without a flower is chosen so that the energy can be concentrated into growing roots. The cut stem is dipped into rooting powder, which contains auxins. Auxins are plant hormones that stimulate cell elongation in the stems. The leaves on the stem are reduced to two or four so that the rate of transpiration is reduced by reducing the number of stomata. The cutting is placed in watered soil. It is important that the soil is not completely saturated with water as this will reduce the oxygen that can reach the roots, reducing the aerobic respiration that occurs. The cutting is then covered with a bag to increase the humidity. This further reduces the transpiration of the cutting.
Micropropagation - Meristem tissue is removed from the shoot tip and axial buds. The meristem tissue contains stem cells. The removed stem cells are called explants. The explants are sterilised and placed in a sterile culture medium that contains auxins and cytokinins to stimulate growth. Everything must be sterilised to prevent contamination of the explants, so they do not grow containing disease, and so that all nutrients are used by the plants for growth and not other microorganisms like bacteria. The explants grow into a callus, which is a mass of identical cells. The callus is then divided to grow into tiny genetically identical plantlets. The plantlets are potted into watered compost to grow into small plants and then planted out.
Advantages
Allows for the rapid production of a large number of individuals, useful for industry
Propagation of individuals with desirable characteristics, for example nice flowers.
Numbers of rare species can be increased, like endangered species.
Production of large numbers of genetically modified or selectively bred individuals.
Propagation of seedless plants, which ensures the production of sterile plants.
Allows for the growth of infertile plants, for example, orchids.
Increases the number of rare/endangered plants.
Quicker than growing from seed. In seeds, many hormones need to be produced and starch stores hydrolysed to allow the plant to grow, which takes a lot more time.
Allows for the growth of pathogen-free individuals as everything is sterilised before use.
Disadvantages
There is a lack of genetic variation, so a monoculture is formed. This means that a disease that kills one of the plants has the potential to kill all the other plants that have been grown.
Population is at a greater risk of environmental change.
The explants are vulnerable to infection.
If the parent plant is infected with microorganisms, the offspring will be too.
The complex aseptic procedures required for sterilisation of the explants is expensive, and requires skilled workers.