A combined 15N tracing/proteomics study in Brassica napus reveals the chronology of proteomics events associated with N remobilisation during leaf senescence induced by nitrate limitation or starvation.

Our goal was to identify the leaf proteomic changes which appeared during N remobilisation that were associated or not associated with senescence of oilseed rape in response to contrasting nitrate availability. Remobilisation of N and leaf senescence status were followed using (15)N tracing, patterns of chlorophyll level, total protein content and a molecular indicator based on expression of senescence-associated gene 12/Cab genes. Three phases associated with N remobilisation were distinguished.

A proteomic profiling approach to reveal a novel role of Brassica napus drought 22 kD/water-soluble chlorophyll-binding protein in young leaves during nitrogen remobilization induced by stressful conditions.

Despite its water-soluble chlorophyll-binding protein (WSCP) function, the putative trypsin inhibitor (TI) activity of the Brassica napus drought 22 kD (BnD22) protein and its physiological function in young leaves during leaf nitrogen (N) remobilization promoted by stressful conditions remains an enigma. Therefore, our objectives were to determine (1) if BnD22 is related to the 19-kD TI previously detected in B. napus young leaves, and (2) if the levels of BnD22 transcripts, BnD22 protein, and TI activity in young leaves are associated with plant responses to stress conditions (N starvation and methyl jasmonate [MeJA] treatments) that are able to modulate leaf senescence.

N-protein mobilisation associated with the leaf senescence process in oilseed rape is concomitant with the disappearance of trypsin inhibitor activity.

Brassica napus L. (oilseed rape) is an important crop plant characterised by low nitrogen (N) use efficiency. This is mainly due to a weak N recycling from leaves that is related to incomplete protein degradation.