II.30. The effect of sodium azide on the cell cycle of the embryonic barley shoot.
By 0. W. Pearson, R. A. Nilan, and C. Sander. Program in Genetics, Department of Agronomy and Soils, Washington State University, Pullman, Washington 99163, USA.
Sodium azide has been utilized recently both as an agent for the study of repair of radiation induced genetic damage and as a mutagen in embryonic shoots in barley caryopses (seeds). However, the effect of this agent on the cell cycle and optimum time of treatment during the cell cycle in these studies is not known. Therefore, a detailed study of the effect of azide on the cell cycle was conducted.
Himalaya barley seeds were treated for 2 hours with 10-4, 5 x 10-4, and 10--3 M oxygenated sodium azide solutions at pH 3. The principle effect on the cell cycle due to sodium azide treatment was a delay in the initiation of metabolism following germination. This resulted in a uniform delay in the following parameters: mitotic activity (Figure 1), seedling growth, and ATP and DNA syntheses.
This delay was interpreted as being due to an ATP deficiency which when alleviated allows the cells to progress normally through mitosis and on through succeeding cell cycles.
Genetic damage caused by sodium azide was not reflected in the seedling heights as the reduction in height was due entirely to mitotic delay. No variation occurred in the progression of cells through mitosis between various regions of the shoot within the first 29 hours of germination.
The data obtained by chemical analysis of the DNA content was inconclusive as far as determining where in the cell cycle the delay occurred. Further investigation with a microspectrophotometer to determine the exact cell stage will be necessary in order to resolve this problem.
