Influence of nitrogen nutrition on the amount of hordein, protein Z and β-amylase messenger RNA in developing endosperms of barley

Abstract

The amount of mRNA encoding hordein, protein Z and β-amylase was analyzed in developing endosperms of the barley variety Bomi and the high-lysine mutant Risø 56. Spikes were cultured in liquid media containing different amounts of ammonium nitrate and endosperms harvested between 15 and 25 days after anthesis. Levels of mRNA were determined by in vitro translations. In addition, B hordein and protein Z mRNA species were titrated by molecular hybridization to cDNAs encoding B hordein and protein Z polypeptides, respectively. Increasing amounts of mRNAs were found in response to increasing nitrogen application. The amount of mRNA for C hordein and protein Z increased linearly with increasing nitrogen concentrations in the medium, whereas the rise in β-amylase mRNA was slight. A concentration of 0.5g×l−1 nitrogen stimulated the transcription of B hordein mRNA, but further increases of nitrogen supply up to 2 g×l−1 resulted in little additional B hordein mRNA production. At high nitrogen levels C hordein and protein Z mRNA are preferentially transcribed whereby these proteins serve as major nitrogen sinks. Hordein and protein Z mRNA are effectively augmented by application of nitrogen after the onset of grain filling and storage protein synthesis. Removal of nitrogen in the medium during grain filling led to a short term decrease in the amounts of these mRNAs. Thus it is possible to modulate the mRNA levels by changing the nitrogen concentration in the medium. The absence of mRNA for B hordein polypeptides in the high-lysine mutant Risø 56, (hor 2 ca), does not influence the effect of nitrogen on the expression of the C hordein, protein Z and β-amylase genes.