Evaluation of sole nitrogen sources for shoot and leaf disc cultures of sugarbeet

Use of single nitrogen sources in nutrient media is essential to ascertaini ng the relative role and regulation of nitrogen assimilatory steps, and may help identify and understand highly productive media for micropropagation and adventitious shoot formation. Eight endogenous nitrogen-containing ions or compounds in sugarbeet (nitrate, ammonium, glutamine, glutamate, urea, proline, glycine betaine and choline) were examined for ability to serve as sole nitrogen source for shoot or leaf disc culture of sugarbeet (Beta vul garis L.) model clone REL-1. The most productive concentrations of nitrate, ammonium, urea, and glutamine as sole nitrogen sources were moderately sup portive of shoot multiplication (64, 70, 81 and 71%, respectively) and fres h weight increase (65, 41, 54 and 41%, respectively) compared to shoot cult ure growth with the Murashige-Skoog nitrogen mix of 40 mM nitrate and 20 mM ammonium. Glutamate and proline were at best poorly supportive, and glycin e betaine and choline were non-supportive. Callus initiation from leaf disc s was supported only by nitrate, ammonium, urea, glutamine and proline (50, 100, 100, 100 and 80%, respectively, at the best concentrations, of that o n Murashige-Skoog medium). Subsequent shoot regeneration from the intact di sc callus in those cultures only occurred on media with nitrate, urea, glut amine, or proline (12, 3, 28 and 3% as many shoots, respectively, as on Mur ashige-Skoog medium). Overall, the Murashige-Skoog nitrogen mix was superio r or equal to any single nitrogen source. However, single nitrogen source m edia with nitrate, ammonium, urea, glutamine or proline should have signifi cant utility for shoot or leaf disc cultures of mutants with impaired nitro gen assimilation, in comparative physiology studies, or in dual cultures wi th pathogens of limited ability to use any of these forms of nitrogen.