Normalization of the DNA content of telophase cells from wheat calli by nutrient modifications.

Cytophotometric analyses were conducted to determine whether the DNA content of wheat callus varied by tissue culture medium or age of callus. Wheat,Triticum aestivum L. line PCYT-20, was cultured on three variations of the Murashige and Skoog (1962) growth medium. At the end of 2, 4, 6 and 8 weeks, samples were collected and prepared for Feulgen cytophotometry. Standards for the DNA measurements were readings from 100 telophase nuclei in wheat meristematic root tips. Amounts of DNA per nucleus present in telophase cells from callus grown on single-strength MS indicated that ploidy level increased 52%, 74% and 39%, respectively, over time from 2, 4, and 6 weeks as compared to the double-strength MS medium, and 29%, 60% and 32%, respectively, when coconut water was added to the single-strength MS culture medium. The shape of the mitotically-active cells in callus was more variable than in root tips cells. Callus grown on double-strength MS medium produced more shoots than callus grown on single-strength MS. Double-strength MS medium and, to a lesser extent, additional sucrose and organic nitrogen overcame the effects of 2,4-D on DNA amplification. Improved media may reduce the somaclonal variation induced by tissue culture.