Chimera (plant)
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Chimeras (or "chimaeras") in botany are usually single organisms composed of two genetically different types of tissue. They occur in plants, on the same general basis as with animal chimeras. However, unlike animal chimeras, both types of tissues may have originated from the same zygote, and the difference is often due to mutation during ordinary cell division.
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[edit] Types of plant chimera
[edit] Variegated plants
The best-known plant chimeras are those cultivated for their variegation. Generally the genetic difference is due to mutation in meristematic tissue of a normal plant. For most variegation, the mutation involved is the loss of the chloroplasts in the mutated tissue, so that part of the plant tissue has no green pigment and no photosynthetic ability. This mutated tissue is unable to survive on its own but is kept alive by its partnership with the normal, photosynthesising tissue.
[edit] Thornless plants
Other types of chimera are valued by gardeners and other horticulturists because the skin tissue lacks the spine-producing characteristic of the underlying tissue.
[edit] Graft-chimeras
A distinct type of plant chimera is the graft-chimera (or, incorrectly, graft-hybrid), involving tissues from two genetically different parents, different cultivars or different species (which may belong to different genera). The tissues may be partially fused together following grafting to form a single growing organism that preserves both types of tissue in a single shoot. The first such known chimera was probably the Bizzaria which is a confusion of the Florentine Citron and the sour orange. Perhaps the best-known example of this is +Laburnocytisus 'Adamii', caused by a fusion of a Laburnum and a broom.
[edit] Propagation
Because chimeras have more than one type of genetic material, while they may produce viable offspring from seed, these will not be true to type. All propagation that preserves the variation has to be by cuttings or division. Some types of cuttings, such as root cuttings, will produce entirely new growing points, usually from the inner one of the two types of tissue, so that these cannot be used either.
[edit] Derivation
The word chimera in these senses is a reference to the monstrous chimera of ancient Greek mythology, a legendary beast made up of parts of several different animals.
