Phytohormone-induced GABA production in transformed root cultures of Datura stramonium: An in vivo¹⁵N NMR study

Primary nitrogen metabolism in transformed root cultures of Datura stramonium was observed by in vivo15N NMR. Treatment of the root cultures with the plant growth regulators α-naphthaleneacetic acid (NAA) and kinetin caused a de-differentiation of the root tissue, together with perturbation of primary and secondary nitrogen metabolism. The levels of newly-synthesized glutamine and glutamate during ammonium assimilation were depleted relative to control cultures, whereas GABA biosynthesis was enhanced. Although GABA production could be stimulated by a decrease in cytoplasmic pH (whether imposed artificially or induced by hypoxia), observation of the roots during phytohormone treatment by31P NMR showed that the cytoplasmic pH remained stable, indicating that the perturbation of nitrogen metabolism in the de-differentiated roots must be due to other causes.