Ploidy levels in transgenic tomato plants determined by chloroplast number.

We determined germline ploidy of primary tomato transformants by counting meiotic chromosomes. We then determined the number of chloroplasts in stomatal cells by cytological staining. A correlation of these values indicated that diploid transformants had significantly fewer chloroplasts than tetraploid transformants. By maximum likelihood, we estimate that less than 1% of diploid transformants will have chloroplast values in the tetraploid range. Transformed plants generally had more chloroplasts than plants derived from seed. Also, there was more variability between transformed than seed derived plants. Less than 5% of transformed plants were chimeric when comparing leaf and pollen ploidy levels. Of 129 transgenic plants examined, 29 (22%) were polyploid.