FREE AMINO-ACID LEVELS AND THE REGULATION OF NITRATE UPTAKE IN MAIZE CELL-SUSPENSION CULTURES

The ability of individual amino acids to regulate nitrate uptake and i nduction was studied in a Zea mays embryo cell line grown in suspensio n culture, The maize cells exhibited a marked preference for absorbing amino acids over nitrate when both were present in culture medium. Th e addition of an individual amino acid (2 mM glutamine, glycine, aspar tic acid, or arginine) to the culture medium with 1 mM nitrate complet ely inhibited nitrate uptake and resulted in a cycle of low levels of nitrate influx followed by efflux to the growth medium. Glutamine was readily absorbed by the cells and was particularly effective in suppor ting optimum cell growth in the absence of an inorganic nitrogen sourc e as compared to the three other amino acids evaluated, However, neith er glutamine nor any of the remaining 19 proteinaceous amino acids app eared to be solely responsible for regulation of nitrate uptake and in duction. The ability of amino acids to regulate nitrate uptake and ass imilation appears to be more related to their overall levels in the ce ll rather than to an accumulation of a specific amino acid.