title: Somaclonal variation is induced de novo via the tissue culture process: a study quantifying mutated cells in Saintpaulia.
abstract: BACKGROUND
  The origin of somaclonal variation has not been questioned previously, i.e., "pre-existing mutations" in explants and "newly induced mutations" arising from the tissue culture process have not been distinguished. This is primarily because there has been no reliable molecular method for estimating or quantifying variation.
  
  
  RESULTS
  We adopted a petal-variegated cultivar of Saintpaulia 'Thamires' (Saintpaulia sp.) as the model plant. Based on the difference between the pre- and post-transposon excision sequence of the promoter region of flavonoid 3', 5'-hydoroxylase (F3'5'H), we estimated mutated (transposon-excised) cell percentages using a quantitative real-time PCR. Mutated cell percentages in leaf laminae used as explants was 4.6 and 2.4% in highly or low variegation flower plants, respectively, although the occurrences of blue color mutants in their regenerants were more than 40%. Preexisting mutated cell percentages in cultured explants were considerably lower than the mutated plant percentage among total regenerants via tissue culture.
  
  
  CONCLUSIONS
  The estimation of mutated cell percentages became possible using the quantitative real-time PCR. The origins of mutations were successfully distinguished; it was confirmed that somaclonal variations are mainly caused by newly generated mutations arising from tissue culture process.
authors.affiliation: Graduate School of Agriculture, Kyoto University, Sakyo-ku, Kyoto, Japan.
authors.forename: Mitsuru
authors.initials: M
authors.lastname: Sato
authors.forename: Munetaka
authors.initials: M
authors.lastname: Hosokawa
authors.forename: Motoaki
authors.initials: M
authors.lastname: Doi
mesh_terms: D002999:Clone Cells; D035264:Flowers / Q000235:genetics; D018506:Gene Expression Regulation, Plant; D014644:Genetic Variation; D019686:Lamiaceae / Q000235:genetics*; D008954:Models, Biological; D009154:Mutation / Q000235:genetics*; D010641:Phenotype; D010858:Pigmentation / Q000235:genetics; D018515:Plant Leaves / Q000235:genetics; D060888:Real-Time Polymerase Chain Reaction; D012038:Regeneration / Q000502:physiology; D015203:Reproducibility of Results; D046509:Tissue Culture Techniques / Q000379:methods*