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      Nitrogen supply influences photosynthesis establishment along the sugarcane leaf

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      Scientific Reports
      Nature Publishing Group UK

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          Abstract

          Nitrogen (N) is a major component of the photosynthetic apparatus and is widely used as a fertilizer in crops. However, to the best of our knowledge, the dynamic of photosynthesis establishment due to differential N supply in the bioenergy crop sugarcane has not been reported to date. To address this question, we evaluated physiological and metabolic alterations along the sugarcane leaf in two contrasting genotypes, responsive (R) and nonresponsive (NR), grown under high- and low-N conditions. We found that the N supply and the responsiveness of the genotype determined the degree of senescence, the carboxylation process mediated by phosphoenolpyruvate carboxylase (PEPcase) and differential accumulation of soluble sugars. The metabolite profiles indicated that the NR genotype had a higher respiration rate in the youngest tissues after exposure to high N. We observed elevated levels of metabolites related to photosynthesis in almost all leaf segments from the R genotype under high-N conditions, suggesting that N supply and the ability to respond to N influenced photosynthesis. Therefore, we observed that N influence on photosynthesis and other pathways is dependent on the genotype and the leaf region.

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          Nitrogen uptake, assimilation and remobilization in plants: challenges for sustainable and productive agriculture.

          Productive agriculture needs a large amount of expensive nitrogenous fertilizers. Improving nitrogen use efficiency (NUE) of crop plants is thus of key importance. NUE definitions differ depending on whether plants are cultivated to produce biomass or grain yields. However, for most plant species, NUE mainly depends on how plants extract inorganic nitrogen from the soil, assimilate nitrate and ammonium, and recycle organic nitrogen. Efforts have been made to study the genetic basis as well as the biochemical and enzymatic mechanisms involved in nitrogen uptake, assimilation, and remobilization in crops and model plants. The detection of the limiting factors that could be manipulated to increase NUE is the major goal of such research. An overall examination of the physiological, metabolic, and genetic aspects of nitrogen uptake, assimilation and remobilization is presented in this review. The enzymes and regulatory processes manipulated to improve NUE components are presented. Results obtained from natural variation and quantitative trait loci studies are also discussed. This review presents the complexity of NUE and supports the idea that the integration of the numerous data coming from transcriptome studies, functional genomics, quantitative genetics, ecophysiology and soil science into explanatory models of whole-plant behaviour will be promising.
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            Important roles of drought- and cold-inducible genes for galactinol synthase in stress tolerance in Arabidopsis thaliana.

            Raffinose family oligosaccharides (RFO) accumulating during seed development are thought to play a role in the desiccation tolerance of seeds. However, the functions of RFO in desiccation tolerance have not been elucidated. Here we examine the functions of RFO in Arabidopsis thaliana plants under drought- and cold-stress conditions, based on the analyses of function and expression of genes involved in RFO biosynthesis. Sugar analysis showed that drought-, high salinity- and cold-treated Arabidopsis plants accumulate a large amount of raffinose and galactinol, but not stachyose. Raffinose and galactinol were not detected in unstressed plants. This suggests that raffinose and galactinol are involved in tolerance to drought, high salinity and cold stresses. Galactinol synthase (GolS) catalyses the first step in the biosynthesis of RFO from UDP-galactose. We identified three stress-responsive GolS genes (AtGolS1, 2 and 3) among seven Arabidopsis GolS genes. AtGolS1 and 2 were induced by drought and high-salinity stresses, but not by cold stress. By contrast, AtGolS3 was induced by cold stress but not by drought or salt stress. All the GST fusion proteins of GST-AtGolS1, 2 and 3 expressed in Escherichia coli had galactinol synthase activities. Overexpression of AtGolS2 in transgenic Arabidopsis caused an increase in endogenous galactinol and raffinose, and showed reduced transpiration from leaves to improve drought tolerance. These results show that stress-inducible galactinol synthase plays a key role in the accumulation of galactinol and raffinose under abiotic stress conditions, and that galactinol and raffinose may function as osmoprotectants in drought-stress tolerance of plants.
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              Genome-wide reprogramming of primary and secondary metabolism, protein synthesis, cellular growth processes, and the regulatory infrastructure of Arabidopsis in response to nitrogen.

              Transcriptome analysis, using Affymetrix ATH1 arrays and a real-time reverse transcription-PCR platform for >1,400 transcription factors, was performed to identify processes affected by long-term nitrogen-deprivation or short-term nitrate nutrition in Arabidopsis. Two days of nitrogen deprivation led to coordinate repression of the majority of the genes assigned to photosynthesis, chlorophyll synthesis, plastid protein synthesis, induction of many genes for secondary metabolism, and reprogramming of mitochondrial electron transport. Nitrate readdition led to rapid, widespread, and coordinated changes. Multiple genes for the uptake and reduction of nitrate, the generation of reducing equivalents, and organic acid skeletons were induced within 30 min, before primary metabolites changed significantly. By 3 h, most genes assigned to amino acid and nucleotide biosynthesis and scavenging were induced, while most genes assigned to amino acid and nucleotide breakdown were repressed. There was coordinate induction of many genes assigned to RNA synthesis and processing and most of the genes assigned to amino acid activation and protein synthesis. Although amino acids involved in central metabolism increased, minor amino acids decreased, providing independent evidence for the activation of protein synthesis. Specific genes encoding expansin and tonoplast intrinsic proteins were induced, indicating activation of cell expansion and growth in response to nitrate nutrition. There were rapid responses in the expression of many genes potentially involved in regulation, including genes for trehalose metabolism and hormone metabolism, protein kinases and phosphatases, receptor kinases, and transcription factors.
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                Author and article information

                Contributors
                lucia@lgf.ib.unicamp.br
                Journal
                Sci Rep
                Sci Rep
                Scientific Reports
                Nature Publishing Group UK (London )
                2045-2322
                2 February 2018
                2 February 2018
                2018
                : 8
                Affiliations
                ISNI 0000 0001 0723 2494, GRID grid.411087.b, Departamento de Genética, Evolução, Microbiologia e Imunologia, , Instituto de Biologia, Universidade Estadual de Campinas, ; 13083-862 Campinas, Brazil
                Article
                20653
                10.1038/s41598-018-20653-1
                5797232
                29396510
                56e8def3-1efd-4641-840b-c509d69c5b46
                © The Author(s) 2018

                Open Access This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The images or other third party material in this article are included in the article’s Creative Commons license, unless indicated otherwise in a credit line to the material. If material is not included in the article’s Creative Commons license and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this license, visit http://creativecommons.org/licenses/by/4.0/.

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