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23.3 CHLOlDPLASl DNA VARlAIlON
Whilst there are many examples of nuclear and mltochondrial DNA variations resulting from
tissue culture, there are very few examples d corresponding changes in the chloroplast DNA.
Day and Ellis (1984) found upto 80% deletion in the major chloroplast DNA molecules in whed
albino plants regenerated from pollen. Sun et al. (1979) observed aiblno plank derived from
anther cultures of rice to contain little or no 23s and 16s RNA and highly reduced levels d
fraction 1 protein.
224 VARlAblm IN DNA MaHYUllON
The role of DNA methylation in controlling gene expression hos been extensively reviewed by
Doedler (1983). Brown and L6rz (1986) observed gross methyidion changes in R2 generation
of maize plank on digestion wlth the i~s~hiZC4ner restriction endonucleases Hpall and Mspi.
They also observed tissue culture induced changes in gene methylation in both nwmd as well
as variant plants. Brown (1989) observed the changes to persist through seveml generations
of sefflng. Phlllips et al. (1992) observed a reduction in methylatton in 34% of the R1 families
studied.
in soybean Quemada et al. (1987) hydrolyzed the 5s gene (CCGG sequences) by both Hpall
and Mrpi. They presumed that DNA tisrue cultured plants Iwked methyidion (CCGG) which
is found In the intact plants (CmeCGG). They propose that tisrue culture condtions prevent
mthyiatlon of thew ritw resullng in suscepltbillty to Hpall or that a mil promon of cells
wmin the Intact plant lack these methyl group and these c.lb are selected during cell
culture. They also obrerve that upon prolonged culluro some cells again became rodstant
to Hpall wggestlng rmuthylatlon d internal cylorine of th. CCGG tehanuclooHde.