In winter wheat (Triticum aestivum L.), post-anthesis nitrogen uptake and remobilisation to the grain correlates with agronomic traits and nitrogen physiological markers
Introduction
To attain maximum yields, modern cereals cultivars require large amounts of fertilizers since the genotypes currently cultivated in developed countries were mostly selected under non-limiting fertilization conditions (Bänziger et al., 1997, Presterl et al., 2003). Among all the fertilizers applied in the field, nitrogen (N) is the most important for plant growth, plant productivity and grain quality (Frink et al., 1999). However, in developed economies, N use efficiency (NUE; defined as grain dry matter per unit of N available from the soil, fertilizer included), is very low and estimated to be approximately 33% (Raun and Johnson, 1999). Thus, in Asia, Europe and Northern America, intensive agricultural practices (Singh, 2005) have led to both higher production costs and a greater risk from environmental hazards such as ground and surface water pollution by nitrate leaching (Mariotti, 1996). Reducing the amount of N fertilizers applied to the field without producing a N deficiency, will be the main challenge faced by breeders in selecting for cereal cultivars that absorb and/or metabolise N more efficiently.
In wheat, grain N content rather than yield components is largely influenced by the amount of N taken up after anthesis and by the amount of remobilised N originating from pre-anthesis uptake since these two sources of N are used for storage protein synthesis (Dupont and Altenbach, 2003). After anthesis, leaves become a source of N. N in leaves is recycled following protein hydrolysis and exported in the form of amino acids to grains (Feller and Fischer, 1994, Masclaux et al., 2000). Sixty to 95% of grain N comes from the remobilisation of N stored in roots and shoots before anthesis (Van Sanford and MacKown, 1986, Palta and Fillery, 1995a, Palta and Fillery, 1995b). A less important fraction of seed N comes from post-flowering N uptake and N translocation to the grain. After flowering, both the size and the N content of the grain can be significantly reduced under N deficient conditions (Dupont and Altenbach, 2003). However, it is still not clear whether it is plant N availability (including the N taken up after anthesis and the remobilised N originating from uptake before anthesis), or storage protein synthesis that limit the determination of grain yield in general and grain protein deposition in particular.
In wheat grown in the field, remobilisation efficiency of the N taken up before anthesis (NRE) was shown to be variable depending on the genotypes examined (Cox et al., 1985, Van Sanford and MacKown, 1987). However, Barbottin et al. (2005) showed that when there are no environmental factors limiting grain filling, the differences in the amount of remobilised N originating from uptake before anthesis were mainly due the capacity of the plant to store N in sink organs until this period. Remobilisation of the N stored before anthesis and N uptake after anthesis are generally estimated by calculating the difference between the amount of total N present at anthesis and the amount of total N present at harvest in the different parts of the plant. However, the results obtained by this method (called apparent remobilisation method) can be subject to large experimental errors due to the necessity to combine data obtained at two different sampling dates. The use of 15N stable isotope labelling is a good alternative that generally allows the estimation of N uptake after anthesis and N remobilisation of pre-anthesis stored N from source organs in a less biased and more precise manner. This was achieved by applying 15N nitrate to maize plants grown in hydroponics (Cliquet et al., 1990) or by infiltrating 15N-urea to the leaves of wheat plants grown the field (Palta and Fillery, 1995a, Palta and Fillery, 1995b). In order to characterize genotypic differences for N remobilisation of the N stored before anthesis and post-anthesis N uptake in wheat, field experiments were conducted on 2 years using post-flowering 15N labelling at high and low levels of N fertilization on five cultivars of winter wheat selected for their different sensitivity to a N stress (Le Gouis et al., 2000). When 15N is applied just after flowering, we showed that both N uptake after flowering and N remobilisation of pre-anthesis stored N can be estimated with a greater accuracy and reproducibility compared to the method measuring the difference between the amount of N present at flowering and the amount of N amount present at maturity. In addition, a critical and statistical analysis of the 15N-labelling technique was performed in comparison with the more traditional N balance method.
To identify physiological traits that may be involved in the control of NUE, we have monitored in parallel the changes in biochemical markers representative of the transition between primary N assimilation during vegetative growth (including nitrate and ammonia assimilation in shoots and roots) and N remobilisation (amino acids released following protein hydrolysis in source organs) during the grain filling period. These biochemical markers including N metabolites (total N, nitrate, ammonium and amino acids) and nitrate reductase (NR), glutamine synthetase (GS) and glutamate dehydrogenase (GDH) activity have been successfully used both in wheat (Kichey et al., 2006) and in maize (Hirel et al., 2005b) to depict the transition sink organs to source organs in the two crop species.
Correlations between the relative values of the physiological markers for N assimilation and recycling, yield and its components, and the capacity of the plant to absorb N after flowering and remobilise the N accumulated before anthesis were then evaluated. We have then determined whether there was any significant genetic correlation between these three classes of traits under low and high N fertilization conditions. In addition, we have examined the influence of the level of N fertilization on these genetic correlations.
Section snippets
Agronomic studies and 15N-labelling experiments
The winter wheat cultivars Arche, Récital, Renan, Shango and Soissons commonly cultivated in France and differing for their response to N deficiency (Le Gouis et al., 2000) were sown on 16 October 2001 and 15 October 2002 at Estrées-Mons INRA experimental station (Somme, northern France) at a density of 250 seeds m−2.
The soil classified as a deep loam soil (Orthic Luvisol, FAO, 2006) contained an average of 190 g clay kg−1, 730 g silt kg−1, 52 g sand kg−1 and 19 g organic matter kg−1 with a pH of 8.1 and its
Estimation of post-anthesis N uptake and remobilisation of N accumulated before anthesis
The repeatability of the estimations of post-anthesis uptake of N was highly improved in 2002 using 15N-labelling (Table 1). In 2003, the apparent remobilisation method and the 15N-labelling method gave approximately the same results. Both in 2002 and 2003, the estimation of the amount of N accumulated before anthesis and further remobilised to the grain was more repeatable using 15N-labelling (Table 1). On average, both methods gave almost the same mean quantities of N taken up after anthesis
Discussion
The amount of N taken up after anthesis and of N remobilised coming from pre-anthesis uptake during grain filling by the five cultivars was different. Both N absorption and N translocation efficiencies were also variable. The changes in metabolite content and enzyme activities representative of N assimilation and N remobilisation during the grain filling period demonstrated that they were subjected to genotypic variability. By the mean of correlation studies we have examined the relationship
Conclusion
In this study we showed that 15N-labeling performed in the field at flowering is a valuable tool to estimate the genetic variability for N uptake, N assimilation and N recycling in different wheat cultivars. This technique combined with the measurement of physiological traits such as GS and NR activities revealed that both enzymes are potential markers to estimate the proportion of N absorbed or N remobilised invested in grain yield elaboration or grain N content. The best way to help breeders
Acknowledgments
Financial support by the Conseil Régional de Picardie (IBFBio project no. 2001.3) is greatly acknowledged. We thank Olivier Delfosse (INRA Laon, France) for realizing the 15N and total N analyses.
References (54)
- et al.
Cumulative effects of cropping systems on the structure of the tilled layer in northern France
Soil Till. Res.
(2002) A rapid and sensitive method for the quantification of microgram quantities of protein utilizing the principle of protein–dye binding
Anal. Biochem.
(1976)- et al.
Field trials with isotopically labeled nitrogen fertilizer
- et al.
Spike dry matter and nitrogen accumulation before anthesis in wheat as affected by nitrogen fertilizer: relationship to kernels per spike
Field Crop Res.
(1999) - et al.
Molecular and biochemical impacts of environmental factors on wheat grain development and protein synthesis
J. Cereal Sci.
(2003) Physiological mechanisms influencing plant nitrogen isotope composition
Trends Plant Sci.
(2001)- et al.
Genetic differences for nitrogen uptake and nitrogen utilisation efficiencies in winter wheat
Eur. J. Agron.
(2000) - et al.
Glutamine synthetase of pea leaves. I. Purification, stabilisation and pH optima
Arch. Biochem. Biophys.
(1973) - et al.
Source:sink ratio and leaf senescence in maize. I. Dry matter accumulation and partitioning during grain filling
Field Crop Res.
(1999) - et al.
Source:sink ratio and leaf senescence in maize. II. Nitrogen metabolism during grain filling
Field Crop Res.
(1999)
Nitrogen redistribution from the roots in post-anthesis plants of spring wheat
Plant Soil
Copper enzymes in isolated chloroplasts, polyphenol oxidase in Beta vulgaris L.
Plant Physiol.
Efficiency of high-nitrogen environment for improving maize for low-nitrogen environment
Crop Sci.
Nitrogen remobilisation during grain filling in wheat: genotypic and environmental effects
Crop Sci.
Variations of wheat leaf C and N isotope compositions after crop fertilization
Compte Rendu de l’Académie des Sciences de Paris
Rapid colorimetric determination of nitrate in plant tissue by nitration of salicylic acid
Commun. Soil Sci. Plant Anal.
Estimation of carbon and nitrogen allocation during stalk elongation by 13C and 15N tracing in Zea mays L.
Plant Physiol.
Genetic variation for nitrogen assimilation and translocation in wheat. II. Nitrogen assimilation in relation to grain yield and protein
Crop Sci.
Nitrogen metabolism in senescing leaves
CRC Crit. Rev. Plant Sci.
Overexpression of nitrate reductase in tobacco delays drought-induced decreases in nitrate reductase activity and mRNA
Plant Physiol.
Nitrogen fertilizer: retrospect and prospect
Proc. Natl. Acad. Sci. U.S.A.
An approach of the genetics of nitrogen use efficiency in maize
J. Exp. Bot.
Modelling postsilking N-fluxes in maize (Zea mays) using 15N-labelling field experiments
New Phytol.
Expression of a conifer glutamine synthetase gene in transgenic poplar
Planta
Prospects for improving nitrogen use efficiency: insights by 15N-labelling experiments
Phytochem. Rev.
Physiology of maize. I. A comprehensive and integrated view of nitrogen metabolism in a C4 plant
Physiol. Plant.
Cited by (342)
Chronic ozone exposure affects nitrogen remobilization in wheat at key growth stages
2024, Science of the Total EnvironmentYield and quality traits of wheat and rapeseed in response to source-sink ratio and heat stress in post-flowering
2024, European Journal of AgronomyEarly share of <sup>15</sup>N-labelled fertilizer between trees and crop in young temperate alley-cropping system
2024, European Journal of AgronomyTowards circular economy: Potential of microalgae – bacterial-based biofertilizer on plants
2024, Journal of Environmental Management