Hybridization of Plants
Hybridization of plants is done to encourage the development of a more desirable plant through the mixing of genetic material from two plants. Manipulating plants genetically dates back to the experiments of Gregor Mendal in the latter half of the eighteenth century. Mendel observed that the offspring of certain plants had physical characteristics similar to the physical characteristics of the plant's parents or ancestors. He examined pea plants to quantify their physical traits in an attempt to predict the traits that would occur n later generations.
It is because of Mendel's work that there are two known factors for each genetic trait, one dominant and the other recessive. The interaction of factors with similar factors from anther plant determines whether the dominant or recessive characteristic is expressed in the offspring.
Mendel's work lead to selective breeding. For a century the creation of a new and hybrid plant was accomplished by mechanically grafting limbs of plants together, or obtaining pollen from a plant and using it to fertilize another plant. The development of tissue culture changed the method and speed at which hybridization is accomplished. Tissue culture is a method of biological research in which fragments of tissue from an animal or plant are transferred to an artificial environment where they can continue to function. The cultured tissue may consist of a single cell, a population of cells or a whole part of a plant.
Through tissue culture, clumps of cells that are more or less different from one another can be obtained. Also, new genetic material can be implanted into the cultured cells and these genetically transformed cells can be induced to divide and grow into complete plants in which every cell will contain the new genetic information.
One method of introducing new genetic material into plant cells is known as somatic cell hybridization. The technique involves taking cultures of the so-called somatic cells (cells concerned with structure or functions other than reproduction) of two different plants and trying to make the cells fuse with one another.
The technique is laborious. To obtain a plant cell, it is often necessary to destabilize it from its neighbors. This can be accomplished by removing the cell wall that surrounds the cell, generating what is called a protoplast. Protoplasts are obtained by mechanical rupture of the walls, of, more commonly, by enzymatic digestion of the wall. Without its cell wall, a protoplast is delicate and must be protected to guard against loss of viability. Embedding the protoplast in a sugar matrix, such as alginate, has been a successful strategy. It is at this stage that the protoplasts can be induced to fuse with protoplasts from another species to from hybrid cells. Chemical agents such as polyethyleneglycol can be added to encourage fusion of the protoplast membranes. Successful fusion also involves fusion of the cell nuclei, forming a hybrid cell containing a mixture of nuclear material--a heterokaryon. Subsequently, heterokaryons are exposed to nutrients--if performed successfully, the cell wall reforms and cell division begins. After several weeks of growth, clumps of cells that have formed can be removed and plated out on a solid source of growth nutrients. Further growth yields a transgenic plant.
Transgenic plants are now also generate using molecular biological techniques of DNA hybridization, whereby the DNA encoding the trait of interest and a gene conferring resistance to an antibiotic or herbicide is inserted into the plant genome. Bacterial vectors can accomplish insertion. The plant tissues are then transferred to a growth substance containing the antibiotic or herbicide. Plants that develop are those that successfully integrated the exogenous DNA.
Uses for transgenic plants are numerous, and include nutritionally improved food crops, plants expressing therapeutic proteins and aesthetically pleasing ornamental plants.
This is the complete article, containing 613 words
(approx. 2 pages at 300 words per page).
