The effect of the source of inorganic nitrogen on growth and enzymes of nitrogen assimilation in soybean and wheat cells in suspension cultures.

Soybean (Glycine max L. cv. Mandarin) and wheat (Triticum monococcum L.) cells were grown in media with NO3 (-) plus NH4 (+) (B5) and NO3 (-) without NH4 (+) (B5-NH4) as nitrogen sources. Changes in pH, [NO3 (-)] and [NH4 (+)] in media, and dry weight, protein content, nitrate reductase (NR) and glutamate dehydrogenase (GDH) in the cells were followed for about 170 h. With both NH4 (+) and NO3 (-) in the medium, NH4 (+) was utilized very quickly. Soybean cells grew poorly in the absence of NH4 (+) while wheat cells grew equally well on media with or without NH4 (+). When soybean cells were grown in medium with NO3 (-) plus NH4 (+), dry weight and NR activity remained relatively low for several hours after which both increased rapidly. This coincided with the time NH4 (+) was depleted from the medium. In the absence of NH4 (+), soybean cell growth and NR activity remained low. NR activity in wheat cells, and GDH activity in soybean and wheat cells, did not vary significantly in the presence or absence of NH4 (+).