Nitrogen Metabolism in Plant Cell Suspension Cultures

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Abstract
Tobacco cells (Nicotiana tabacum) are capable of growth on ammonia as a sole N soucre only when succinate, malate, fumarate, citrate, .alpha.-ketoglutarate, glutamate or pyruvate is added to the growth medium. A ratio between the molar concentrations of ammonia to succinate (as a complementary organic acid) in the growth medium of 1.5 was optimal. Succinate had no effect on the rate of uptake of ammonia from the medium into the cells although it affected the intracellular concentration of ammonia. The changes were not sufficient to explain inhibition of growth as being due to ammonia toxicity. The radioactivity from 14C-succinate was incorporated into malate, glutamate and aspartate within 2 min. Apparently the role of organic acids is neither connected to ammonium transport nor to relief of ammonia toxicity, but may be related to the need for additional C skeletons for synthesis of amino acids.