The recent literature has repeatedly reported that silver nitrate (AgNO3) might increase the frequency of the differentiation of friable calli of maize and the other cereals. As a result of this, it led to the increase of somatic embryogenesis. The amount of silver nitrate employed in the reports ranged from 0.5 to 100µM. In order to make further experiments on this effect, two maize callus lines, 87-54 and SAN1, from anther culture in vitro, were chosen. The medium N6 with eight percent sucrose; 1mg/l kinetin and 0.5mg/l 2,4-D, was prepared. For each callus line, 15 dishes of medium were inoculated; five of them were controls without AgNO3, five, with 50µM AgNO3, and the other five, 100µM AgNO3. On the average, each dish had 30 pieces of actively growing callus. They were kept in a temperature range of 65 to 75 F. Six weeks later, friable calli appeared on both callus lines grown on the medium with both 50 and 100µM AgNO3. None was found for those on the control medium. Then the calli were subcultured on the same but freshly prepared medium. Two weeks after transfer, white and compact pro-embryos occurred in many of the calli for those on both 50 and 100µM AgNO3 media. None were observed on the controls. By actual counting of the number of pro-embryos, it was concluded that medium with 50µM AgNO3 was more effective in callus differentiation as well as pro-embryo induction than that with 100µM AgNO3.
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