Increased Chromosomal Variation in Transgenic versus Nontransgenic Barley (Hordeum vulgare L.) Plants

Abstract

Plants from in vitro culture can exhibit somaclonal variation, two characteristics 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 transgenic callus of approximately the same age; chromosomes were studied in cells from callus and root tips from plants. Analysis of these data revealed greater variation in ploidy in transgenic compared with nontransgenic plants. Of 59 independent transgenic lines, only 32 (54%) had normal diploid complements of 2n = 2x = 14, while 27 (46%) were tetraploid (2n = 4x = 28) or aneuploid around the tetraploid level (i.e., 26, 27, 29 and 30 chromosomes); no aneuploidy around the diploid number was observed. Nontransgenic plants regenerated after in vitro culture alone had a much lower percentage of tetraploids (0–4.3%). Most diploid plants had normal gross morphology, while tetraploid plants had abnormal morphological features. Ploidy determinations were made on randomly selected cells from callus of immature embryos cultured for 0 to 14 d. The number of tetraploid cells in 1‐d‐ to 7‐d‐old callus was around 2 to 4%; in callus comparable in age to that used to regenerate both the transgenic and the nontransgenic sets of plants, 23% of the cells were tetraploid. This percentage is lower than the percentage (46%) of tetraploid 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 callus and nontransgenic plants, the extent of ploidy changes in transgenic plants is exacerbated, perhaps due to the additional stresses that occur during transformation.

Estimating a binomial proportion from several independent samples

“…Using data from all four cultivars, the average proportion of hairy roots expressing GUS is p-A if the arithmetic average method is adopted, in comparison to a larger estimate of p-W with the weighted average method. The difference in the overall proportion estimates is c. 2%, which is relatively large in comparison to the published data found from other available sources (Chen et al 2000;Choi et al 2000;Paderson & Brink 2000). This is because for most of the published data the differences between sample sizes n i and between the individual sample proportion estimates are small, so that differences betweenp-A andp-W are also small.…”

“…In practice, p-W has been advocated both in quality control (Pitt 1994) and in some statistical textbooks (Ott 1993 ;Ott & Mendenhall 1994), whereas p-A has not been found to be recommended in any text books. Even among recent publications of the same journal, some researchers have used the weighted method (Chen et al 2000;Choi et al 2000;Paderson & Brink 2000). Others, however, still adopt the arithmetic average approach (Narayanan et al 1999;Casler & van Santen 2000;Ismail et al 2000).…”

Barley

“…Golden Promise indicate that callus and plants derived from nontransgenic and transgenic callus of approximately the same age had varying levels of ploidy variation after performing chromosomal analysis. Nontransgenic plants regenerated after in vitro culture had a lower percentage of ploidy variation (0-4.3%), compared to transgenics of which 46% were tetraploid or aneuploid around the tetraploid level (Choi et al, 2000); tetraploid plants had abnormal morphological features. Ploidy determinations were also made on randomly selected cells from callus of immature embryos and the number of tetraploid cells in 1-day and 7-day-old cultures was 2-4%.…”

“…The report also shows that somaclonal variation was accentuated by the transformation procedure. This supposition is based on chromosomal analyses of callus and plants from in vitro-cultured nontransgenic and transgenic barley lines (Choi et al, 2000; see also Section 2.1.1). A higher percentage (78%) of karyotypically abnormal cells was observed in transgenic barley callus cultures, compared with 15% of cytologically abnormal cells in nontransgenic callus and aspects of the transformation process, i.e., osmotic treatment and selection pressure, appeared to have triggered the cytological abnormalities (Choi et al, 2001).…”

Field Supervisory Test of DREB-Transgenic Populus: Salt Tolerance, Long-Term Gene Stability and Horizontal Gene Transfer

“…The fixed integration of foreign genes into the genomes of trees and their subsequent stable expression are essential for the further use of transgenic trees in forest tree breeding programs [1,2]. Unstable expression of a transgene in receptor plants can be due to both intrinsic factors, including a long lifecycle, difficulty in transformation and the general absence of sexual propagation before field release [3,4] and to the effects of the environment and stress [5].…”