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Plant Tissue Culture

• in vitro propagation

• Rapid (compared to outdoors)

• Asexual

Used for1. Micropropagation 2. Regeneration

Vegetative (asexual) Propagation Occurs in Nature

• Layering - a drooping lower branch contacts the soil (pressed down by snow or vegetation); roots form at point of soil contact forming a new genetically identical tree

• When trees of some species are cut down, new shoots emerge from the stump

• strawberries spread through sending out above-ground horizontal shoots called runners, also called stolons.

• in vitro propagation (in tubes/petri plates etc.)• Rapid• Asexual

Example: A Potato plant is superior because it has good moisture and starch content. (good for french fries!)

I. Micropropagation - Many genetically identical plants are produced from ONE PLANT

A single node will produce a shoot within 4-6 weeks that has 4-6 nodes. 

Each plantlet can be "subcultured" to produce another 4-6 plants each.

Micropropagation

• Hundreds of thousands of plants could be developed from one node

• Since these are produced from axillary buds, the plantlets will be clones of the mother plant.

Micropropagation of almost all the fruit crops and vegetables is possible

• Some examples: dwarfing sweet cherry, Shade trees, Ornamental shrubs, Roses, Clematis, Lilacs, Saskatoon berries, Nutraceutical Plants, Rhododendron, Azalea, mustard, corn, soybeans, wheat, rice, cotton, tomato, potato, citrus, turf, legumes

Advantages of Micropropagation• economical in time and space

• greater output -can produce millions of uniformly flowering and yielding plants– African Biotechnologies - fruit crops banana

and indoor pot flowers- 6 million pieces per year

• disease free

• elite plants with exceptional characteristics

Advantages Cont’d

• facilitates safer movements of germplasm across nations - In vitro germplasm assures the exchange of pest and disease free material

• great for – vegetatively reproduced crops – crops which produce few seeds or highly

heterozygous seeds.

II. Regeneration - The process whereby a part of a plant can be turned into a whole new plant

African violet leaf sprouting new shoots

Regeneration is possible because plant cells can be made totipotent using hormones.

• differentiated tissue: stems, leaves, roots, etc.• undifferentiated (embryonic) cells are totipotent:

can become a whole new plant by differentiating into a whole new plant.

Cytokinins induce the production of shoots

Auxins induce the production of roots

The action of the different hormones / regulators is not consistent:

• Different plants will respond to the same chemical differently.

• Different plant parts from the same plant can respond differently

Plant Hormones are naturally occurring chemicals that influence plant growth. Growth Regulators are synthetic versions of hormones.

Steps involved in Tissue Regeneration

• tissue must be sterile - completely free of any microoganisms; done using aseptic technique

1 Starting tissue is called an explant: differentiated cells (these cells have developed to be part of specialized tissue (root, leaf, stem, ovary, cotyledon, etc.).

Explants are plated on a sterile petri dish containing hormones and nutrients that promote the explant cells to develop into Callus - a mass of undifferentiated cells.

Callus cells are totipotent

Tobacco Regeneration

3. Individual cells (or clumps of cells) of the callus are transferred aseptically to a different petri dish containing sterile medium that encourages the undifferentiated callus cells to become shoots and roots.

One mass of callus cells can be divided and transferred to many plates for development into shoots and roots.

4. Once shoots and roots have developed, they are transferred to soil and grown to maturity.

• Plants that develop from existing terminal or axillary buds are true clones of the "mother plant".

• Meristematic buds tend to be protected from variations caused by environmental factors.

• Little or no variation usually occurs when this method of tissue culture is used.

Micropropagation vs. Regeneration

• Regeneration using callus can produce variants of the original plant

• Non-meristematic cells are not protected from variations caused by the environment.

• When these cells experience a mutation, the plants that are produced from them will also show a difference from the “mother plant”.

Micropropagation vs. Regeneration (cont’d)

Tissue Culture is also used when plants are Genetically Engineered

Plants that receive a new gene are called Transgenic plants or GMOs

A Genetically Engineered Plant has a New Gene

• Squash gets coat proteins from Cucumber or zucchini virus to prevent viral disease (to vaccinate the squash)

• Corn gets a gene from bacteria that allows it to survive in the presence of weedkiller (one that is less harmful to environment that other herbicides).

• Corn gets a gene from different bacteria that allows it to produce its own pesticide (protects against insects).

After a new gene is given to a plant, scientists must figure out how to regenerate the transformed plant cell.