Breakage of Chromosomes by Oxygen

Abstract

Dry pollen grains of Tradescantia paludosa were exposed in various ways to O2 gas of 99.5% purity, then cultured on a lactose-agar-colchicine medium in a moist chamber. Flower heads were treated in a similar fashion, and entire plants were exposed to O2 under bell jars. Control expts. showed no chromosomal effect by methods of handling. The frequency of aberrations was approx. the same whether O2 was flushed through the cells at normal pressure or whether there was repeated evacuation and gas admission. An expt. using 100% pure O2 indicated that the aberrations were due to the O2 and not to the .4% of contaminants. As the O2 pressure was increased the effect was also increased. Long exposure times or high pressures affected the chromosomes so drastically that only fragments were found in most dividing nuclei. The results of keeping pollen in complete darkness for 30 min. before treatment and 3 hrs. afterwards showed that the O2 effect was independent of light. An increase in O2 concn. gave an increase in chromosomal aberrations, with chromatid and isochromatid deletions appearing to increase as a power of O2 concn. By interpolation an equal effect was produced by 65% 02 for 1 hr. and 350r of X-rays. The effect of air (20% O2) at 5 atm. was less than that of 100% O2 at 1 atm. There appeared to be an exponential relationship between effect of O2 and length of time of exposure. In microspores and microsporocytes chromosomal aberrations were induced by growing plants for 4 days in a slow constant flow of O2 and by exposing the inflorescences for 3 hrs. to O2 at 100 lbs. pressure, but there was a high degree of killing of treated buds.