Cytological Variation Exacerbated by Transformation Process in Transgenic Cereal and Grass Plants

Recent results reveal that high frequencies of cytogenetic abnormalities occur in transgenic barley, oat and orchardgrass plants generated from either immature embryos or highly regenerative, green tissues via microprojectile bombardment, compared with nontransgenic plants: barley (45% vs. 0%), oat (58% vs. 0-6.3%) and orchardgrass (70% vs. 0%). Further analysis of cytological status of transgenic plants of wheat, tall fescue and another set of oat plants generated by a different tissue culture method also indicated that higher cytological variation occurred in transgenic plants of wheat, tall fescue and oat compared with nontransgenic plants: wheat (36% vs. 0%), oat (31% vs. 7%) and tall fescue (50% vs. 17%). The most common cytological variation in the transgenic hexaploid species (2n = 6x = 42), oat, wheat and tall fescue, was aneuploidy, followed by deletion of chromosomal segments; no changes in ploidy level were observed. In contrast, ploidy changes were the major cytological variation in diploid transgenic barley (2n = 2x = 14) and tetraploid transgenic orchardgrass (2n = 4x = 28) plants. These data indicate that additional stresses imposed by the transformation process in addition to those encountered with the in vitro culture process alone affect cytological variation in transgenic plants. Another conclusion from these studies is that the nature of the chromosomal aberration, e.g., strict ploidy changes or aneuploidy, appears to be dependent upon the fundamental genomic state of the particular plant species used for in vitro culture and transformation.