BREAKAGE OF CHROMOSOMES IN Tradescantia WITH A CALCIUM DEFICIENCY

Abstract

Clonal divisions of a single plant of Tradescantia paludosa were grown in culture solutions containing 2.5, 10 (suboptimal) and 250 (optimal) ppm of Ca. Plants grown at the lowest concentration for 3 months were transferred to solns. lacking Ca. Plants grown in 10 ppm for 3 months were transferred to 2.5 ppm. For 10 out of 14 plants grown in 250 ppm the pH of the Initial soln. was 5.8, for the other 4 plants the soln. was adjusted to pH 5.5 each week. Buds were collected during the 6th and 7th months for chromosomal observations. Anthers from plants in the lowest Ca concn. had only abortive cells with no microspore divisions, but anthers from plants grown at the other 2 Ca levels had complete division cycles. There were 9.7% more chromosomal aberrations in plants grown in suboptimal Ca than in those grown in optimal Ca., with a highly significant difference between the 2 groups. Observations for micronuclei at a stage just before prophase indicated that plants in suboptimal Ca had 4.42 more micronuclei than those in optimal Ca and that most of the micronuclei were due to chromosomal structural changes. Pollen grains containing micronuclei were 17.3 times more frequent in plants grown in suboptimal Ca than in those grown in optimal Ca. There was a correlation between frequencies of pollen grains with micronuclei and aborted grains for the former group, none for the latter. In other studies of plants grown in low Ca, the proportional increase of X-ray-induced chromosome fragments and interstitial deletions was higher than the increase of dicentric and centric rings. It was concluded that bivalent cations such as Ca and Mg may bind together the chromosomal nucleoprotein, providing structural stability.