Nitrogen in the plant cell culture media is provided by either ammonia or nitrate salt. In the media

• utilization of ammonium cause culture pH to drop while utilization of nitrate cause culture pH to rise
• utilization of nitrate cause culture pH to drop while utilization of ammonium cause culture pH to rise
• utilization of both ammonium and nitrate result in rise in pH
• utilization of both ammonium and nitrate result in drop in pH