When the cell wall of the plant cell is mechanically or enzymatically (cellulase and pectinase) removed the naked cells are known as protoplast. The protoplast remains biologically active and in tissue culture the somatic cell protoplasts are induced to fuse to produce somatic hybrids and cybrids.
The protoplast fusion is induced by polyethylene glycol (PEG) or by application of pulses of high voltage electric current. When protoplasts of two different cell lines are induced to fuse, it results in coalescence of cytoplasms. The nuclei of two protoplasts may or may not fuse even after fusion of cytoplasms.
The resulting binucleate cells are known as heterokaryons or hetcrocytcs. When the two nuclei are fused a somatic hybrid is produced. But, when cytoplasm is fused and one of the two nuclie is lost a cybrid or cytoplasmic hybrid or heteroplast is produced. The fused protoplasts are grown on suitable nutrients medium. The protoplasts regain cells walls, divide to form callus and finally develop to plant lets.
Both hybrids and cybrids have their utility in crop improvement. Through protoplast fusion somatic hybrids of genetically different cell lines or species can be produced. These genetically different cell lines are otherwise not sexually compatible for sexual hybridization procedures.
In the field of pest and disease resistance and transfer of some qualitative and quantitative characters somatic hybridization through protoplast fusion has shown good results.
Some genetic factors are carried in cytoplasmic inheritance, like male sterility in some plants, susceptibility and resistance to some pathotoxins and drugs etc. Therefore, production of cybrids can help in transfer of cytoplasmic genetic information. Cybrid technology has been successfully applied to Rice, carrot, Brassica sp. Citrus, tobacco and sugar beet. Anther culture and production of haploids
Anther; the male reproductive organ after microsporogenesis contains pollens or microspores which are haploid anthers or pollens are cultured to raise haploid plants these haploids may not be of any commercial use but can be subjected to colchicine treatment to double their chromosome number so that completely homozygous diploid plants can be obtained.
The haploid plants can also be useful in screening of recessive mutation because in diploids or polyploids screening of recessive mutation is not possible.