Search

Plant nitrogen nutrition is an essential topic in biology that should be included in scientific education. Nitrogen availability is one of the primary limiting factors for plant growth, and these organisms are the primary support for the pluricellular terrestrial life, since they are the fundamental group of autotrophs. For this reason, the use of nitrogen fertilizers is in the basis of the Green Revolution that led to an extraordinary increase in the food production during the twentieth century. To illustrate the importance of plant nitrogen nutrition, a new laboratory experience for students is presented in this manuscript. The aim of the following laboratory teaching activity is training of students through the evaluation of metabolic, biochemical, and molecular markers that are related to the nitrogen nutritional status of plants. For this purpose, cherry tomato plants (Solanum lycopersicum var. cerasiforme) were used, since they exhibit rapid growth and good differential biomass accumulation in response to changes in the nitrogen supply. The proposed laboratory experiment enables the development of the entire protocol for postgraduate students or in a reduced version for students from lower educational levels. © 2019 International Union of Biochemistry and Molecular Biology, 47(4):450-458, 2019., (© 2019 International Union of Biochemistry and Molecular Biology.)

Nitrogen (N) is frequently a limiting factor for tree growth and development. Because N availability is extremely low in forest soils, trees have evolved mechanisms to acquire and transport this essential nutrient along with biotic interactions to guarantee its strict economy. Here we review recent advances in the molecular basis of tree N nutrition. The molecular characteristics, regulation, and biological significance of membrane proteins involved in the uptake and transport of N are addressed. The regulation of N uptake and transport in mycorrhized roots and transcriptome-wide studies of N nutrition are also outlined. Finally, several areas of future research are suggested., (© The Author 2017. Published by Oxford University Press on behalf of the Society for Experimental Biology. All rights reserved. For permissions, please email: journals.permissions@oup.com.)

PpDof 5 is a regulator of the expression of glutamine synthetase (GS; EC 6.3.1.2) genes in photosynthetic and non-photosynthetic tissues of maritime pine. We have used Arabidopsis thaliana as a model system to study PpDof 5 function in planta, generating transgenic lines overexpressing the pine transcription factor. The overexpression of PpDof 5 resulted in a substantial increase of lignin content with a simultaneous regulation of carbon and nitrogen key genes. In addition, partitioning in carbon and nitrogen compounds was spread via various secondary metabolic pathways. These results suggest pleiotropic effects of PpDof 5 expression on various metabolic pathways of carbon and nitrogen metabolism. Plants overexpressing PpDof 5 exhibited upregulation of genes encoding enzymes for sucrose and starch biosynthesis, with a parallel increase in the content of soluble sugars. When the plants were grown under nitrate as the sole nitrogen source, they exhibited a significant regulation of the expression of genes involved mainly in signaling, but similar growth rates to wild-type plants. However, plants grown under ammonium exhibited major induction of the expression of photosynthetic genes and differential expression of ammonium and nitrate transporters. All these data suggest that in addition to controlling ammonium assimilation, PpDof 5 could be also involved in the regulation of other pathways in carbon and nitrogen metabolism in pine trees., (© 2015 Scandinavian Plant Physiology Society.)

Quantitative trait loci (QTLs) for the main steps of nitrogen (N) metabolism in the developing ear of maize (Zea mays L.) and their co-localization with QTLs for kernel yield and putative candidate genes were searched in order to identify chromosomal regions putatively involved in the determination of yield. During the grain-filling period, the changes in physiological traits were monitored in the cob and in the developing kernels, representative of carbon and N metabolism in the developing ear. The correlations between these physiological traits and traits related to yield were examined and localized with the corresponding QTLs on a genetic map. Glycine and serine metabolism in developing kernels and the cognate genes appeared to be of major importance for kernel production. The importance of kernel glutamine synthesis in the determination of yield was also confirmed. The genetic and physiological bases of N metabolism in the developing ear can be studied in an integrated manner by means of a quantitative genetic approach using molecular markers and genomics, and combining agronomic, physiological and correlation studies. Such an approach leads to the identification of possible new regulatory metabolic and developmental networks specific to the ear that may be of major importance for maize productivity., (© 2012 INRA. New Phytologist © 2012 New Phytologist Trust.)

During the grain-filling period of maize, the changes in metabolite content, enzyme activities, and transcript abundance of marker genes of amino acid synthesis and interconversion and carbon metabolism in three lines F2, Io, and B73 have been monitored in the cob and in the kernels. An integrative statistical approach using principal component analysis (PCA) and hierarchical clustering of physiological and transcript abundance data in the three maize lines was performed to determine if it was possible to link the expression of a physiological trait and a molecular biomarker to grain yield and its components. In this study, it was confirmed that, in maize, there was a genetic and organ-specific control of the main steps of nitrogen (N) and carbon metabolism in reproductive sink organs during the grain-filling period. PCA analysis allowed the identification of groups of physiological and molecular markers linked to either a genotype, an organ or to both biological parameters. A hierarchical clustering analysis was then performed to identify correlative relationships existing between these markers and agronomic traits related to yield. Such a clustering approach provided new information on putative marker traits that could be used to improve yield in a given genetic background. This can be achieved using either genetic manipulation or breeding to increase transcript abundance for the genes encoding the enzymes glutamine synthetase (GS), alanine amino transferase (AlaAT), aspartate amino transferase (AspAT), and Δ1-pyrroline-5-carboxylate synthetase (P5CS).

Nitrogen (N) metabolism was characterized in the developing ear of glutamine synthetase deficient mutants (gln1-3, gln1-4 and gln1-3/gln1-4) of maize exhibiting a reduction in kernel yield. During the grain-filling period, the metabolite contents, enzyme activities and steady-state levels of transcripts for marker genes of amino acid synthesis and interconversion were monitored in the cob and kernels. The ear of gln1-3 and gln1-3/gln1-4 had a higher free amino acid content and a lower C/N ratio, when compared to the wild type. The free ammonium concentrations were also much higher in gln1-3/gln1-4, and Asn accumulation was higher in gln1-3 and gln1-3/gln1-4. The level of transcripts of ZmAS3 and ZmAS4, two genes encoding asparagine synthetase, increased in the 'aborted kernels' of gln1-3 and gln1-3/gln1-4. The results show that N metabolism is clearly different in developing and 'aborted kernels'. The data support the hypothesis that N accumulated in 'aborted kernels' is remobilized via the cob to developing kernels using Asn as a transport molecule. The two genes ZmAS3 and ZmAS4 are likely to play an important role during this process., (© 2010 INRA. Plant Biotechnology Journal © 2010 Society for Experimental Biology and Blackwell Publishing Ltd.)

*The main steps of nitrogen (N) metabolism were characterized in the developing ear of the two maize (Zea mays) lines F2 and Io, which were previously used to investigate the genetic basis of nitrogen use efficiency (NUE) in relation to yield. *During the grain-filling period, we monitored changes in metabolite content, enzyme activities and steady-state levels of transcripts for marker genes of amino acid synthesis and interconversion in the cob and the kernels. *Under low N fertilization conditions, line Io accumulated glutamine, asparagine and alanine preferentially in the developing kernels, whereas in line F2, glutamine and proline were the predominant amino acids. Quantification of the mRNA-encoding enzymes involved in asparagine, alanine and proline biosynthesis confirmed that the differences observed between the two lines at the physiological level are likely to be attributable to enhanced expression of the cognate genes. *Integrative analysis of physiological and gene expression data indicated that the developing ear of line Io had higher N use and transport capacities than line F2. Thus, in maize there is genetic and environmental control of N metabolism not only in vegetative source organs but also in reproductive sink organs.

A pine asparagine synthetase gene expressed in developing seedlings has been identified by cloning its cDNA (PsAS1) from Scots pine (Pinus sylvestris L.). Genomic DNA analysis with PsAS1 probes and a sequence-based phylogenetic tree are consistent with the possibility of more than one gene encoding asparagine synthetase in pine. However, the parallel patterns of free asparagine content and PsAS1 products indicate that the protein encoded by this gene is mainly responsible for the accumulation of this amino acid during germination and early seedling development. The temporal and spatial patterns of PsAS1 expression together with the spatial distribution of asparagine content suggest that, early after germination, part of the nitrogen mobilized from the megagametophyte is diverted toward the hypocotyl to produce high levels of asparagine as a reservoir of nitrogen to meet later specific demands of development. Furthermore, the transcript and protein analyses in seedlings germinated and growth for extended periods under continuous light or dark suggest that the spatial expression pattern of PsAS1 is largely determined by a developmental program. Therefore, our results suggest that the spatial and temporal control of PsAS1 expression determines the re-allocation of an important amount of seed-stored nitrogen during pine germination.