Leaf senescence and nitrogen remobilization efficiency in oilseed rape (Brassica napus L.)

Abstract

Despite its worldwide economic importance for food (oil, meal) and non-food (green energy and chemistry) uses, oilseed rape has a low nitrogen (N) use efficiency (NUE), mainly due to the low N remobilization efficiency (NRE) observed during the vegetative phase when sequential leaf senescence occurs. Assuming that improvement of NRE is the main lever for NUE optimization, unravelling the cellular mechanisms responsible for the recycling of proteins (the main N source in leaf) during sequential senescence is a prerequisite for identifying the physiological and molecular determinants that are associated with high NRE. The development of a relevant molecular indicator (SAG12/Cab) of leaf senescence progression in combination with a (15)N-labelling method were used to decipher the N remobilization associated with sequential senescence and to determine modulation of this process by abiotic factors especially N deficiency. Interestingly, in young leaves, N starvation delayed senescence and induced BnD22, a water-soluble chlorophyll-binding protein that acts against oxidative alterations of chlorophylls and exhibits a protease inhibitor activity. Through its dual function, BnD22 may help to sustain sink growth of stressed plants and contribute to a better utilization of N recycled from senescent leaves, a physiological trait that could improve NUE. Proteomics approaches have revealed that proteolysis involves chloroplastic FtsH protease in the early stages of senescence, aspartic protease during the course of leaf senescence, and the proteasome β1 subunit, mitochondria processing protease and SAG12 (cysteine protease) during the later senescence phases. Overall, the results constitute interesting pathways for screening genotypes with high NRE and NUE.

Nitrogen use efficiency in rapeseed. A review

“…phase sequentially, multiple overlapping source-sink situations are possible in rapeseed. This asynchrony between N source availability in old leaves and N requirements in seeds, along with incomplete protein hydrolyzation in the source organs, can lead to noteworthy N losses from fallen leaves (Aufhammer et al 1994;Diepenbrock 2000;Rossato et al 2001;Malagoli et al 2005a;Ulas et al 2013;Avice and Etienne 2014). Leaf senescence is therefore a critical stage at the intersection of N uptake and N remobilization in the reproductive organs (Schulte auf'm Erley et al 2007).…”

<b>Different nitrogen and boron levels influence the grain production and oil content of a sunflower cultivar

“…Because crops are demanded in such large amounts, the agricultural sector relies greatly on N and often improperly uses it, which threatens air, water and soil quality (Xu, Fan, & Miller, 2012). The search for genotypes that efficiently use N by optimizing N fertilization has been the subject of several studies on important agronomical crops (Avice & Etienne, 2014). N is essential for sunflower grain production and oil extraction (Rasool, Hassan, & Jahangir, 2013).…”

Changes in Leaf Characteristics with Tree Age in <i>Dryobalanops beccarii</i> Dyer in a Restored Forest of Sarawak, Malaysia

“…The N, P and Mg are key nutrients that influence a number of important leaf traits, which vary in the use and allocation between leaves. These N, P and Mg are highly mobile and always being remobilized in young leaves (Avice and Etienne, 2014;Fischer, 2008;Mediavilla and Escudero, 2003), causing deficiency symptom in old leaves. The inadequate supply of N, P and Mg in soil may reduce the N, P and Mg in the leaves over time.…”

“…The mobility of each macronutrient differs depending on the degree of deficiency in the leaves (Avice and Etienne, 2014;Fischer, 2008). The mobile macronutrients such as N, P, K and Mg are readily translocated from old leaves to new growth, leading to deficiencies in older leaves.…”