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.