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Nitrogen (N) nutrition impacts on primary carbon metabolism and can lead to changes in δ13C of respired CO2. However, uncertainty remains as to whether (1) the effect of N nutrition is observed in all species, (2) N source also impacts on respired CO2 in roots and (3) a metabolic model can be constructed to predict δ13C of respired CO2 under different N sources. Here, we carried out isotopic measurements of respired CO2 and various metabolites using two species (spinach, French bean) grown under different NH4+:NO3− ratios. Both species showed a similar pattern, with a progressive 13C‐depletion in leaf‐respired CO2 as the ammonium proportion increased, while δ13C in root‐respired CO2 showed little change. Supervised multivariate analysis showed that δ13C of respired CO2 was mostly determined by organic acid (malate, citrate) metabolism, in both leaves and roots. We then took advantage of nonstationary, two‐pool modelling that explained 73% of variance in δ13C in respired CO2. It demonstrates the critical role of the balance between the utilisation of respiratory intermediates and the remobilisation of stored organic acids, regardless of anaplerotic bicarbonate fixation by phosphoenolpyruvate carboxylase and the organ considered. Summary statement: Phaseolus vulgaris and Spinacia oleracea grown under varying NH4+:NO3− ratio show 13C‐depletion in leaf‐respired CO2 as NH4+ proportion increases. Supervised multivariate analysis shows that δ13C of respired CO2 is mostly determined by malate‐citrate metabolism in leaves and roots of both species. [ABSTRACT FROM AUTHOR]

Summary statement: Day respiration is a net flux resulting from several CO2‐generating and CO2‐fixing reactions, not only related to catabolism but also to anabolism. We review pieces of evidence that decarboxylating reactions are partly fed by carbon sources disconnected from current photosynthesis and how they reflect various metabolic pathways. [ABSTRACT FROM AUTHOR]

Water deficit causes substantial yield losses that climate change is going to make even more problematic. Sustainable agricultural practices are increasingly developed to improve plant tolerance to abiotic stresses. One innovative solution amongst others is the integration of plant biostimulants in agriculture. In this work, we investigate for the first time the effects of the biostimulant –Leafamine®–a protein hydrolysate on greenhouse lettuce (Lactuca sativa L.) grown under well-watered and water-deficit conditions. We examined the physiological and metabolomic water deficit responses of lettuce treated with Leafamine® (0.585 g/pot) or not. Root application of Leafamine® increased the shoot fresh biomass of both well-watered (+40%) and deficit-irrigated (+20%) lettuce plants because the projected leaf area increased. Our results also indicate that Leafamine® application could adjust the nitrogen metabolism by enhancing the total nitrogen content, amino acid (proline) contents and the total protein level in lettuce leaves, irrespective of the water condition. Osmolytes such as soluble sugars and polyols, also increased in Leafamine®-treated lettuce. Our findings suggest that the protective effect of Leafamine is a widespread change in plant metabolism and could involve ABA, putrescine and raffinose. [ABSTRACT FROM AUTHOR]

Isotopic analyses of plant samples are now of considerable importance for food certification and plant physiology. In fact, the natural nitrogen isotope composition (δ15N) is extremely useful to examine metabolic pathways of N nutrition involving isotope fractionations. However, δ15N analysis of amino acids is not straightforward and involves specific derivatization procedures to yield volatile derivatives that can be analysed by gas chromatography coupled to isotope ratio mass spectrometry (GC-C-IRMS). Derivatizations other than trimethylsilylation are commonly used since they are believed to be more reliable and accurate. Their major drawback is that they are not associated with metabolite databases allowing identification of derivatives and by-products. Here, we revisit the potential of trimethylsilylated derivatives via concurrent analysis of δ15N and exact mass GC-MS of plant seed protein samples, allowing facile identification of derivatives using a database used for metabolomics. When multiple silylated derivatives of several amino acids are accounted for, there is a good agreement between theoretical and observed N mole fractions, and δ15N values are satisfactory, with little fractionation during derivatization. Overall, this technique may be suitable for compound-specific δ15N analysis, with pros and cons. [ABSTRACT FROM AUTHOR]

It is common practice to manipulate CO2 and O2 mole fraction during gas‐exchange experiments to suppress or exacerbate photorespiration, or simply carry out CO2 response curves. In doing so, it is implicitly assumed that metabolic pathways other than carboxylation and oxygenation are altered minimally. In the past few years, targeted metabolic analyses have shown that this assumption is incorrect, with changes in the tricarboxylic acid cycle, anaplerosis (phosphoenolpyruvate carboxylation), and nitrogen or sulphur assimilation. However, this problem has never been tackled systematically using non‐targeted analyses to embrace all possible affected metabolic pathways. Here, we exploited combined NMR, GC–MS, and LC–MS data and conducted non‐targeted analyses on sunflower leaves sampled at different O2/CO2 ratios in a gas exchange system. The statistical analysis of nearly 4,500 metabolic features not only confirms previous findings on anaplerosis or S assimilation, but also reveals significant changes in branched chain amino acids, phenylpropanoid metabolism, or adenosine turn‐over. Noteworthy, all of these pathways involve CO2 assimilation or liberation and thus affect net CO2 exchange. We conclude that manipulating CO2 and O2 mole fraction has a broad effect on metabolism, and this must be taken into account to better understand variations in carboxylation (anaplerotic fixation) or apparent day respiration. It is generally assumed that metabolic pathways other than carboxylation and oxygenation are altered minimally by changing CO2 and O2 conditions during gas exchange. Using isotope‐assisted metabolomics analyses, we show that manipulating CO2 and O2 has a broad effect on different major metabolic pathways, and this must be taken into to better interpret variations in carboxylation (anaplerotic fixation) or apparent day respiration. [ABSTRACT FROM AUTHOR]

Nitrogen (N) nutrition impacts on primary carbon metabolism and can lead to changes in δ 13 C of respired CO 2 . However, uncertainty remains as to whether (1) the effect of N nutrition is observed in all species, (2) N source also impacts on respired CO 2 in roots and (3) a metabolic model can be constructed to predict δ 13 C of respired CO 2 under different N sources. Here, we carried out isotopic measurements of respired CO 2 and various metabolites using two species (spinach, French bean) grown under different NH 4 + :NO 3 - ratios. Both species showed a similar pattern, with a progressive 13 C-depletion in leaf-respired CO 2 as the ammonium proportion increased, while δ 13 C in root-respired CO 2 showed little change. Supervised multivariate analysis showed that δ 13 C of respired CO 2 was mostly determined by organic acid (malate, citrate) metabolism, in both leaves and roots. We then took advantage of nonstationary, two-pool modelling that explained 73% of variance in δ 13 C in respired CO 2 . It demonstrates the critical role of the balance between the utilisation of respiratory intermediates and the remobilisation of stored organic acids, regardless of anaplerotic bicarbonate fixation by phosphoenolpyruvate carboxylase and the organ considered., (© 2024 The Author(s). Plant, Cell & Environment published by John Wiley & Sons Ltd.)

We describe here a method to study and manipulate photorespiration in intact illuminated leaves. When the CO 2 /O 2 mole fraction ratio changes, instant sampling is critical, to quench leaf metabolism and thus trace rapid metabolic modification due to gaseous conditions. To do so, we combine 13 CO 2 labeling and gas exchange, using a large custom leaf chamber to facilitate fast sampling by direct liquid nitrogen spraying. Moreover, the use of a high chamber surface area (about 130 cm 2 ) allows one to sample a large amount of leaf material to carry out 13 C-nuclear magnetic resonance (NMR) analysis and complementary analyses, such as isotopic analyses by high-resolution mass spectrometry (by both GC and LC-MS). 13 C-NMR gives access to absolute 13 C amounts at the specific carbon atom position in the labeled molecules and thereby provides an estimate of 13 C-flux of photorespiratory intermediates. Since NMR analysis is not very sensitive and can miss minor metabolites, GC or LC-MS analyses are useful to monitor metabolites at low concentrations. Furthermore, 13 C-NMR and high-resolution LC-MS allow to estimate isotopologue distribution in response to 13 CO 2 labeling while modifying photorespiration activity., (© 2024. The Author(s), under exclusive license to Springer Science+Business Media, LLC, part of Springer Nature.)

It is common practice to manipulate CO 2 and O 2 mole fraction during gas-exchange experiments to suppress or exacerbate photorespiration, or simply carry out CO 2 response curves. In doing so, it is implicitly assumed that metabolic pathways other than carboxylation and oxygenation are altered minimally. In the past few years, targeted metabolic analyses have shown that this assumption is incorrect, with changes in the tricarboxylic acid cycle, anaplerosis (phosphoenolpyruvate carboxylation), and nitrogen or sulphur assimilation. However, this problem has never been tackled systematically using non-targeted analyses to embrace all possible affected metabolic pathways. Here, we exploited combined NMR, GC-MS, and LC-MS data and conducted non-targeted analyses on sunflower leaves sampled at different O 2 /CO 2 ratios in a gas exchange system. The statistical analysis of nearly 4,500 metabolic features not only confirms previous findings on anaplerosis or S assimilation, but also reveals significant changes in branched chain amino acids, phenylpropanoid metabolism, or adenosine turn-over. Noteworthy, all of these pathways involve CO 2 assimilation or liberation and thus affect net CO 2 exchange. We conclude that manipulating CO 2 and O 2 mole fraction has a broad effect on metabolism, and this must be taken into account to better understand variations in carboxylation (anaplerotic fixation) or apparent day respiration., (© 2020 John Wiley & Sons Ltd.)

Breast cancer is the most common cancer in women worldwide. Despite the information provided by anatomopathological assessment and molecular markers (such as receptor expression ER, PR, HER2), breast cancer therapies and prognostics depend on the metabolic properties of tumor cells. However, metabolomics have not provided a robust and congruent biomarker yet, likely because individual metabolite contents are insufficient to encapsulate all of the alterations in metabolic fluxes. Here, we took advantage of natural 13 C and 15 N isotope abundance to show there are isotopic differences between healthy and cancer biopsy tissues or between healthy and malignant cultured cell lines. Isotope mass balance further suggests that these differences are mostly related to lipid metabolism, anaplerosis and urea cycle, three pathways known to be impacted in malignant cells. Our results demonstrate that the isotope signature is a good descriptor of metabolism since it integrates modifications in C partitioning and N excretion altogether. Our present study is thus a starting point to possible clinical applications such as patient screening and biopsy characterization in every cancer that is associated with metabolic changes.