NITROGEN FERTILIZATION INCREASES AMMONIUM ACCUMULATION DURING SENESCENCE OF BARLEY LEAVES.

NADIA ROLNY; MARIELA BAYARDO; JUAN JOSÉ GUIAMET; LORENZA COSTA

ACTA PHYSIOLOGIAE PLANTARUM

SPRINGER HEIDELBERG

Lugar: HEIDELBERG; Año: 2015

0137-5881

Leaf senescence is a developmental process characterized by two events: 1-completedegradation of chloroplasts and, 2-nitrogen remobilization to other parts of the plant.During senescence chloroplast proteins are degraded into amino acids and ammonium.Most of the ammonium is re-assimilated into amino acids for export from the senescingleaf, whereas a minor part is lost as NH3 emitted from the leaves. The amount ofammonia emitted depends of the amount of NH3accumulated in the substomatal cavityof mesophylls cells, which is continuously re-supplied with NH41+ from the cytoplasm.Ammonia accumulation in tissues could increase the possibility of loss of N as NH3emitted. In this report we analyzed the effect of N fertilization on nitrogen metabolismduring senescence of barley leaves during the vegetative and reproductive stages ofdevelopment. During senescence of barley leaves protein degradation was accompaniedby transient ammonia accumulation at both, vegetative and reproductive stages ofdevelopment. The peak of ammonium occurred immediately after major proteindegradation in all samples analyzed, thereafter levels of ammonium clearly decreased.N accumulated as ammonium during senescence of barley leaves represented a highpercentage of protein-N, i.e., approximately 5% in primary leaves and 16% in flagleaves. A significant increase of ammonium peak concentration was observed whendoses of N fertilizer increased, mainly at the reproductive stage, where the percentage ofN accumulated as ammonium reached near 35% of protein-N. Cytosolic glutaminesynthetase (GS1) transcript levels were up regulated during senescence of the flag leaf,but they were down regulated by increases in N availability. These results suggest thatthe decreases of ammonia levels after its peak may be more closely related to NH3emission than to GS assimilation.