Effects of glutamine and K-glutamate on assimilation of [15N]-nitrate during auxin treatment for root formation in vitro (Pinus pinaster)

In order to establish the relationship of nitrogen nutrition to root formation in vitro, efficiency of various forms of nitrogen supply was investigated in micropropagated shoots of Pinus pinaster. Nitrate (3.3 m M as N) containing medium supplemented with glutamine (2 m M as N) resulted in optimal rooting (control medium) whereas the rooting response was inhibited by the presence of glutamate (2 m M as N) in the medium. Study of ¹⁵NO⁻₃ behaviour in shoots cultured on the control medium showed a marked increase of ¹⁵N incorporation during the second half of a period of auxin treatment (total duration 16 days). The majority of the nitrogen incorporated from the medium was accumulated into protein in the rooting zone. Autoradiography of [³H]-thymidine in this reacting zone showed strong DNA synthesis at this time. Addition of glutamate both prevented the root formation process and resulted in a marked slowdown of nitrate uptake and decrease of protein synthesis.