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Cytoplasm Transfer - Conventionally, cytoplasm transfer from one strain into another is achieved by the backcross method, which requires 6-7 years. Cytoplasm can be transferred in one year only by somatic hybridization using one of the following two schemes:
(1) fusion between especially treated protoplasts of two strains, and
(2) fusion between protoplast of one strain and cytoplasts of another strain. In addition,
(3) cytoplasm can also be transferred by ordering a symmetric hybrid into a backcross programme.
In the first scheme, protoplast of the strain/species into which the cytoplasm is to be transferred (parent A) is treated with a suitable concentration of iodoacetate. This treatment inactivates the mitochondria of these protoplasts; therefore, this approach achieves substitution of mitochondria of this strain species, by that of the other fusion partner.

The protoplasts of the other species/strain (parent B) are irradiated with a suitable dose of y- or X-rays to inactivate their nuclei. The somatic hybrids obtained by fusion of the protoplasts of parent A and parent B would contain the nucleus of parent A, and mitochondria of parent B; their chloroplasts could be either from parent A or B or, sometimes, a recombinant between the two. This approach not only transfers the mitochondria in one year only, but also transfers them across sexually incompatible species.

Cybrids, in essence, contain nucleus from one species but cytoplasm from, both the species involved in fusion. This approach has been used to transfer cytoplasmic male sterility and triazine resistance in tobacco, cabbage, rice, potato and Petunia.

Cybrids also provide opportunity for combining mitochondria of one species with chloroplasts of another species, and of generating recombinant organelles, especially mitochondria. This may be an important objective in several cases.

For example, B. napus alloplasmic lines carrying radish (Raphanus sativus) cytoplasm (Ogura cytoplasm) are male sterile but show chlorophyll deficiency under low temperatures. Cybrids were produced between CMS (Ogura cytoplasm) B. napus and normal male fertile B napus.

Some of the cybrid regenerants were male sterile but did not show chlorophyll deficiency under low temperatures; these cybrids contained radish mitochondria and B. napus chloroplasts.

 
 

 
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