CHROMATIN COMPOSITION IN MAIZE F1 HYBRIDS

Recent studies have demonstrated unexpected nuclear DNA content in Fl hybrids of maize. Flow cytometry was used to determine what portions o f the nuclei were affected. Nuclei were isolated from eight maize inbr ed lines and seven Fl hybrids. The nuclei were stained with PI and wer e analyzed on a flow cytometer-cell sorter. The PI/DAPI ratios were ca lculated for each line. From these ratios, the amount of heterochromat in and euchromatin was estimated for different maize inbreds and speci fic Fl hybrids. The inheritance pattern of both heterochromatin and eu chromatin in Fl hybrids was studied. Tn some Fl hybrids, there was inc reased heterochromatin amount with no increase in total DNA. In other hybrids, total DNA increase was associated with an increase in the amo unt of heterochromatin. C-banding analysis was performed to determine if variation in knob number was responsible for this variation. The kn ob number in each Fl hybrid was as predicted from the parental lines e xcept in two hybrids. In addition, relative abundance of the knob sequ ence present in the G1 nuclei of Fl hybrids was determined by sorting nuclei and hybridizing with knob DNA sequences. The hybridization resu lts indicated that the amount of knob DNA increases. The increase in k nob DNA is not enough, however, to account for the rotal increase in h eterochromatin and/or total nuclear DNA. These results demonstrate the role of heterochromatinization when two parental genomes are combined in a F1 hybrid genome. Chromatin structure changes within hybrid nucl ei appear to be necessary far proper organization of the Fl genome.