Increased chromosomal variation in transgenic versus nontransgenic barley (Hordeum vulgare L.) plants

Plants from in vitro culture can exhibit somaclonal variation, two characte ristics of which are structural rearrangements and variation in chromosome number. These characteristics were studied in barley (Hordeum vulgare L. cv . Golden Promise) callus and plants derived from nontransgenic and transgen ic callus of approximately the same age; chromosomes were studied in cells from callus and root tips from plants. Analysis of these data revealed grea ter variation in ploidy in transgenic compared with nontransgenic plants. O f 59 independent transgenic lines, only 32 (54%) had normal diploid complem ents of 2n = 2x = 14, while 27 (46%) were tetraploid (2n = 4x = 28) or aneu ploid around the tetraploid level (i.e., 26, 27, 29 and 30 chromosomes); no aneuploidy around the diploid number was observed. Nontransgenic plants re generated after in vitro culture alone had a much lower percentage of tetra ploids (0-4.3%). Most diploid plants had normal gross morphology, while tet raploid plants had abnormal morphological features. Ploidy determinations w ere made on randomly selected cells from callus of immature embryos culture d for 0 to 14 d. The number of tetraploid cells in 1-d- to 7-d-old callus w as around 2 to 4%; in callus comparable in age to that used to regenerate b oth the transgenic and the nontransgenic sets of plants, 23% of the cells w ere tetraploid. This percentage is lower than the percentage (46%) of tetra ploid plants from the transgenic lines; however, it is considerably higher than the percentage (0-4.3%) of tetraploid plants from nontransgenic callus . Therefore, although chromosomal variation and abnormalities occur in call us and nontransgenic plants, the extent of ploidy changes in transgenic pla nts is exacerbated, perhaps due to the additional stresses that occur durin g transformation.