Plant Tissue Culture
Investigating the Practical Applications of Vegetative Propagation
Aug 26, 2009
As early as 1902, the German botanist Gottlieb Haberlandt suggested that all living plant cells are totipotent. That is, he believed each cell possesses the potential to develop into an entire plant. However, he was never able to prove it experimentally.
The Beginnings of Plant Tissue Culture
In the late 1950s, F.C. Steward isolated small bits of phloem tissue from carrot root and placed them in a liquid growth medium in a rotating flask. The growth medium he used contained sucrose, certain vitamins, and coconut milk, which Steward knew to be rich in plant growth compounds (although the nature of these compounds was not then understood).
In the rotating flask, individual cells continuously broke away from the growing cell mass and floated free in the medium. These individual cells were able to grow and divide and some even formed clumps with roots. When these cell clumps were transferred to agar plates, the clumps produces shoots.
When the clumps with roots and shoots were planted in soil, they developed into normal carrot plants eventually flowering and producing seed. Thus, yet another type of vegetative propagation known as tissue culture became available.
The Process of Plant Tissue Culture
Tissue culture involves the production of new plants from pieces of tissue placed on sterile nutrient growth medium. The cell clumps (known as a callus) that develop eventually grow into tiny plantlets with roots and stems. When these plantlets are transplanted into soil, they grow into full-sized plants.
A great advantage of tissue culture is that millions of identical plants can be grown from only a small amount of tissue. Tissue culture is used in the commercial production of orchids, houseplants, cut flowers, fruit plants, and ornamental trees, shrubs, and non-woody plants.
Most of the time, plantlets produced from a single callus are genetically identical, or clones; however, mutations sometimes occur giving rise to a plantlet with different characteristics. Variants that develop by this technique may have useful traits.
In one study at a New Jersey biotechnology company, 230 tomato plantlets were generated from callus that developed from tomato leaf tissue. When mature, 13 plants showed unique traits, including larger fruit, tangerine-colored fruit, and denser (fleshier) fruit. Mutant traits developed this way are passed on to the offspring of these plants and can lead to commercially successful new varieties.
In addition to searching for new traits, scientists can select for specific mutant types by exposing developing callus cells to certain poisonous substances. Those cells that survive have genes that provide resistance to the poison. The resulting plants and their offspring should also show resistance to this chemical.
A useful application of this technique is in the development of crop varieties, corn, for example, that are resistant to herbicides (weed killers). This permits widespread herbicide application to a cultivated crop without damage to the crop plant. This technique is agriculturally significant because weed control is a meaningful way to increase crop yields, since weeds compete with crops for nutrients, harbor pests, and clog irrigation systems.
Why Use Plant Tissue Culture?
Plant tissue culture methods offer certain advantages over traditional methods of vegetative propagation allowing plant scientists to:
- Produce exact copies (clones) of plants that have desired traits such a large flowers or tasty fruits.
- Quickly produce many mature plants without the need of pollination and seed formation.
- Clean a particular plant of viral and bacterial infections thus producing disease-free stock for agriculture or horticulture.
- Develop whole plants from genetically modified cells.
- Produce plants that are difficult to grow from seeds.
Plant tissue culture combined with genetic engineering techniques has given plant scientists the ability to create new plant species at will.
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