CHROMOSOME ENDOREDUPLICATION IN ENDOSPERM CELLS OF 2 MAIZE GENOTYPES AND THEIR PROGENIES

Chromosome endoreduplication is a very common process in higher plants but its function and genetic control are still to be clarified. In ou r experiments we analyzed, by Feulgen cytophotometry, chromosome endor eduplication in endosperm cells of two maize genotypes, IHP and ILP, h aving high and low protein content in their seed, respectively. Chromo some endoreduplication occurs in both lines within 24 days after polli nation, attaining a maximum ploidy level of 384C (7 DNA replication ro unds) in IHP and of 192C (6 replication rounds) in ILP. In the mature seed, endosperms of the two lines show different mean ploidy level. In reciprocal crosses between IHP and ILP the F-1 endosperms have mean p loidy levels analogous to that of the maternal parent, showing that th e difference in ploidy level between the two genotypes is maintained. After selfing of the F-1 plants, the difference in ploidy level betwee n the two F-2 populations is reduced. In F-2 the mean ploidy level is as variable as in F-1, indicating the absence of genetic segregation. From our data, it is apparent that both the genetic constitution (cyto plasmic and nuclear) of the maternal parent and the genotype of the in dividual endosperms influence the ploidy level. An analysis of the pro tein content in endosperms carried out on the same seed sample as anal yzed cytophotometrically showed that the protein content increases, du ring seed development, parallel to chromosome endoreduplication and va ries, in the two lines, in reciprocal crosses and their progeny, accor ding to the same trend as mean ploidy level, suggesting a correlation between the two parameters.