The challenge of remobilisation in plant nitrogen economy. A survey of physio‐agronomic and molecular approaches

Abstract

SummaryIn this article, we discuss the ways in which our understanding of the controls of nitrogen remobilisation in model species and crop plants have been increased through classical physiological studies and the use of transgenic plants or mutants with modified capacities for nitrogen or carbon assimilation and recycling. An improved understanding of the transition between nitrogen assimilation and nitrogen recycling will be vital, if improvements in crop nitrogen use efficiency are to reduce the need for excessive input of fertilisers and improve or stabilise yield. In this review, we present an overall view of past work and more recent studies on this topic, using different plants systems and models depicting the biochemical and molecular events occurring during the transition between sink leaves and source leaves. These models may provide a way to identify the nature of the metabolic or developmental signals triggering in a coordinate manner nitrogen and carbon recycling during leaf senescence.Another way of developing crop varieties with improved nitrogen use efficiency, and identifying key elements controlling the process of nitrogen remobilisation, is the use of quantitative genetics. We present and discuss recent findings on the genetic variability and basis of nitrogen use efficiency in crops in general and in maize in particular. A genetic approach using maize recombinant inbred lines was undertaken allowing the detection of Quantitative Trait Loci (QTLs) for morphological traits, grain yield and its components under high nitrogen or low nitrogen input. Co‐mapping was observed between genes encoding enzymes involved in nitrogen assimilation (nitrate reductase, glutamine synthetase) and these Quantitative Trait Loci. All coincidences were consistent with the expected physiological function of the corresponding enzyme activities. This work strongly suggests that in maize, nitrogen use efficiency can be improved both by marker‐assisted selection and genetic engineering.

Improving Nitrogen Use Efficiency in Crops for Sustainable Agriculture

“…Recently the hypothesis that GDH plays an important role in controlling glutamate homeostasis has been put forward [142]. This function, which may have a signaling role at the interface of C and N metabolism, may be of importance under certain phases of plant growth and development when there is an important release or accumulation of ammonia [144][145][146].…”

Absorption et assimilation du nitrate et recyclage de l’azote organique chez les plantes : intérêt pour le colza

“…Le mécanisme envisagé est un système de transport actif secondaire, comme défini pré-cédemment. L'absorption du nitrate entraîne en général une alcalinisation du milieu exté-rieur, ce qui suggère que des protons pénè-trent dans la cellule en même temps que les ions NO 3 -, ou bien que ces derniers sont échangés contre des ions OH -, ce qui revient au même. Les études électrophysiologiques ont montré de plus que le transport de nitrate est associé à une dépolarisation membranaire, le système est donc électrogène.…”

“…En effet, son affinité très faible pour l'ammonium est incompatible avec un rôle majeur dans l'assimilation primaire de l'azote. Il est supposé que la GDH jouerait plutôt un rôle prépondérant dans la désamination du glutamate et la formation d'a-cétoglutarate ; cette hypothèse est cohé-rente avec l'induction de l'activité observée pendant la germination et la sénescence, deux périodes pendant lesquelles le catabolisme des acides aminés est important [3].…”

Spectral Remote Sensing of the Responses of Soybean Plants to Environmental Stresses

“…Increasing leaf photosynthetic rates appear to be a straightforward way of increasing crop yields. Considerable physiological research has been carried out to select and breed for genotypes with superior photosynthetic rates, and was successful in identifying such cultivars in maize, wheat and soybean (Masclaux et al, 2001;Habash et al, 2001;Sinclair et al, 2000). In soybean, the trait is inherited quantitatively (Sall & Sinclair, 1991).…”