The nature of the genetic control of Endosperm Balance Number based on aneuploid analysis of Datura

The genetic control of Endosperm Balance Number (EBN), a mechanism of effec tive ploidy that controls seed development, was studied using aneuploidy. T he Endosperm Balance Number hypothesis proposes that each species has an ef fective ploidy (EBN) in the endosperm and that it is the effective ploidies , rather than the numerical (actual) ploidies, that must be in a 2:1 matern al to paternal ratio for normal endosperm development. Experiments were con ducted in Datura stramonium L. (2n=4x=48) to determine if more than one chr omosome but less, than the whole genome could change the EBN of the female. Triploids were crossed with tetraploids to produce aneuploids. Most plump seeds gave rise to 2n=4x=48 chromosome plants. Six plants had between 38 an d 47 chromosomes. Karyotyping of these plants supported the conclusion that only two chromosomes (1.2 and 19.20), when extra, were necessary to change the EBN of the central cell.