Variability in components of harmful nitrogen during growth of sugarbeet genotypes

In quality assessment and in breeding, (alpha-amino-N is taken as the only representative for all components of harmful nitrogen of sugarbeet. The aim of the present study was therefore to investigate whether the selection for a low (alpha-amino-N content in the beet affects also other soluble N compounds or other organs. Furthermore, the physiological mechanisms underlying the changes in the a-amino-N content should be elucidated. Two genotypes were grown in field trials at three locations. They were choosen with respect to their different a-amino-N concentration in the beet. The results indicate that a reduction of the (alpha-amino-N content by selection does probably not affect all components of harmful nitrogen, but predominantly glutamine metabolism. Effects on the concentrations of nitrate, protein and betaine were not evident. Differences in the concentrations of glutamine and (alpha-amino-N in the beet were due to differences in the activity of glutamine synthetase in beet and crown. Interestingly, genotypic differences were hardly observed in the blades and stems of the leaves. The genotypic differences in beet and crown increased with increasing plant age but they were measurable already at the first harvest time point (I I I days after sowing).