Nitrogen fertilization increases ammonium accumulation during senescence of barley leaves

ROLNY N.; BAYARDO M.; GUIAMET J.J.; COSTA M.L.

ACTA PHYSIOLOGIAE PLANTARUM

SPRINGER HEIDELBERG

Lugar: HEIDELBERG; Año: 2016 vol. 38 p. 1 - 11

0137-5881

Abstract Leaf senescence is a developmental processcharacterized by two events: (1) dismantling of the photosyntheticapparatus and, (2) nitrogen remobilization toother parts of the plant. Ammonium accumulation duringsenescence of barley leaves was produced by chloroplastproteins degradation. Although most of the ammonium isremobilized as amino acids from senescing leaves, a minorpart is lost as NH3 emitted across stomata. The amount ofammonia emitted depends on the amount of NH3 accumulatedin the substomatal cavity, which is continuouslyre-supplied with NH41? from the cytoplasm of neighboringcells. Ammonia accumulation in tissues could increase thepossibility of loss of N as NH3 emitted. In this report weanalyzed the effect of N fertilization on nitrogen metabolismduring senescence of barley leaves during the vegetativeand reproductive stages of development. Duringsenescence of barley leaves protein degradation wasaccompanied by transient ammonium accumulation at bothstages of development. The peak of ammonium occurredimmediately after major protein degradation in all samplesanalyzed, thereafter levels of ammonium clearly decreased.N accumulated as ammonium during senescence of barleyleaves represented a high percentage of protein-N, i.e.,approximately 16 % in primary leaves and 23 % in flagleaves. A significant increase of ammonium peakconcentration was observed when doses of N fertilizerincreased, mainly at the reproductive stage, where thepercentage of N accumulated as ammonium reached near35 % of protein-N at that stage. Vascular cytosolic glutaminesynthetase (Hv GS1_1) transcript levels wereupregulated during senescence of the flag leaf, but theywere downregulated by increases in N availability. Theseresults suggest that the decreases of ammonia levels afterits peak may be more closely related to NH3 emission thanto N re-assimilation by GS.