Increased nuclear DNA content in developing cotton fiber cells

The nuclear DNA content of developing cotton fiber cells (Gossypium hirsutum, cv. MD51ne) increases similar to 24% after 2 d postanthesis (dpa). The amount of nuclear DNA at 2 dpa is 5.4 +/- 0.27 pg. At 3-4 dpa it increases to 6.7 +/- 0.24 pg and by 5 dpa it is 6.8 +/- 0.70 pg. These values were obtained by nuclear fluorescence after staining with Hoechst 33258. Human oral squamous cell nuclei were used as a DNA standard. Nuclear DNA content increases in fibers growing on either fertilized or unfertilized ovules. The increase also is detectable in Feulgen stained nuclei using two-wavelength cytospectrophotometry. All measurements were made on isolated fiber cell nuclei using a newly developed method tailored to cotton fiber cells. The results imply that during the early stages of development fiber cell nuclei either selectively amplify certain sequences or enter S-phase replicating a portion of their genome.