Vegetative propagation, tissue culture and cloning
In vegetative propagation, new plants grow from a root, stem or leaf. Laboratories also raise plants by tissue culture, and the sheep Dolly was made by cloning.
Natural vegetative propagation
| Plant part | Special structure | Examples |
|---|---|---|
| Root | Adventitious roots (roots that grow from unusual places) | Sweet potato, dahlia |
| Stem | Runner: a stem that grows along the ground and strikes roots | Lawn grass |
| Stem | Sucker: a side shoot that grows up from an underground stem | Chrysanthemum |
| Stem | Bulb | Onion |
| Stem | Tuber: a swollen underground stem with buds (eyes) | Potato |
| Stem | Rhizome: a thick underground stem | Ginger, canna |
| Leaf | Adventitious buds in the notches of the leaf edge | Bryophyllum |
Artificial vegetative propagation (used by farmers and nurseries)
| Method | How it is done | Examples |
|---|---|---|
| Cutting | A piece of branch is cut and planted in soil; it forms roots and grows | Rose, money plant |
| Layering | A branch is bent to the ground and part of it is buried; it strikes roots there and is then cut free | Jasmine, grapevine |
| Gootee (air layering) | A ring of bark is removed from a branch. The spot is covered with moist soil and tied. Roots form there, and the branch is then cut off and planted | Litchi, pomegranate |
| Grafting | A cut shoot of the wanted plant (the scion) is fitted into a slit in the stem of a rooted plant (the stock). It is tied, and the two join and grow as one | Citrus, mango |
Why people use vegetative propagation
People took the idea from nature. Farmers and nursery owners use these methods to multiply a plant they like, such as a mango tree with sweet fruit. The new plants are like the parent, because they grow from its own body. They often flower and fruit sooner than plants grown from seed. Plants that make few or no good seeds, such as banana and many roses, can still be grown.
Tissue culture (micropropagation) and cloning
Every living plant cell is **totipotent**: it can grow into a whole plant. This is because all the cells of a plant came from one zygote, so all carry the same genes, and genes control growth.
- 1Take a small piece of a plant, such as a bit of leaf or of carrot root.
- 2Grow its cells in a nutrient solution. They form a lump of undifferentiated cells, the callus.
- 3Add the right hormones and nutrients. The callus forms tiny new plants, called plantlets.
- 4Plant them out. Raising plants in this way is micropropagation: many plants from one tiny piece.Used for plants such as orchids and chrysanthemum
- 5Cloning in animals: the nucleus of an udder cell of a sheep was put into an egg cell whose own nucleus had been removed.
- 6★The egg grew into an embryo inside a surrogate mother (a female that carries another's embryo). The lamb, Dolly, was an exact genetic copy, a clone, of the sheep that gave the nucleus.
★ key step
Activity: grow a money plant from a cutting
- 1Cut a healthy piece of money plant stem, or a champa branch, about 15 to 20 cm long. It should have a few nodes: the points where leaves join the stem.
- 2Remove the lowest leaves, so that one or two nodes are bare.
- 3Stand the cutting in a bottle of water, or plant it in moist soil with the bare nodes covered.
- 4Keep it in bright light but out of strong sun. Change the water every few days, or keep the soil moist.
- 5Observe after one or two weeks: white roots grow from the nodes, and later new leaves appear.
- 6★Conclusion: a whole new plant grew from a piece of stem. This is vegetative propagation by cutting.
★ key step
Nurseries across India sell grafted mango and lemon saplings that fruit in a few years and keep the parent's taste. Tissue culture labs supply farmers with large numbers of healthy, identical banana plantlets.
2 marks: “Which stem structure helps each of these to propagate: potato, onion, ginger and lawn grass?” Potato: tuber. Onion: bulb. Ginger: rhizome. Lawn grass: runner.
2 marks: “What is a callus? How is it used in tissue culture?” An undifferentiated mass of cells grown from a small piece of plant in a nutrient solution. With the right hormones and nutrients, it forms new plantlets.
3 marks: “A potato sprouts new plants from its eyes on its own, while a farmer grafts mango plants. How do artificial methods differ from natural ones, and how do they help farmers? Give two points.” Natural: new plants arise by themselves from roots, stems or leaves. Artificial: people cut, layer, gootee or graft plants on purpose. Benefits: many plants of a chosen kind, raised quickly; they keep the parent's qualities; plants with few seeds can be grown.
Potato Tuber, Onion Bulb, Ginger Rhizome, Grass Runner.