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Carbon isotope discrimination (∆) in leaf biomass (∆ BL ) and tree rings (∆ TR ) provides important proxies for plant responses to climate change, specifically in terms of intrinsic water-use efficiency (iWUE). However, the nonphotosynthetic 12 C/ 13 C fractionation in plant tissues has rarely been quantified and its influence on iWUE estimation remains uncertain. We derived a comprehensive, ∆ based iWUE model (iWUE com ) which includes nonphotosynthetic fractionations (d) and characterized tissue-specific d-values based on global compilations of data of ∆ BL , ∆ TR and real-time ∆ in leaf photosynthesis (∆ online ). iWUE com was further validated with independent datasets. ∆ BL was larger than ∆ online by 2.53‰, while ∆ BL and ∆ TR showed a mean offset of 2.76‰, indicating that ∆ TR is quantitatively very similar to ∆ online . Applying the tissue-specific d-values (d BL  = 2.5‰, d TR  = 0‰), iWUE estimated from ∆ BL aligned well with those estimated from ∆ TR or gas exchange. ∆ BL and ∆ TR showed a consistent iWUE trend with an average CO 2 sensitivity of 0.15 ppm ppm -1 during 1975-2015. Accounting for nonphotosynthetic fractionations improves the estimation of iWUE based on isotope records in leaf biomass and tree rings, which is ultimate for inferring changes in carbon and water cycles under historical and future climate., (© 2024 The Author(s). New Phytologist © 2024 New Phytologist Foundation.)

Although primarily studied in relation to photorespiration, serine metabolism in chloroplasts may play a key role in plant CO 2 fertilization responses by linking CO 2 assimilation with growth. Here, we show that the phosphorylated serine pathway is part of a 'photosynthetic C 1 pathway' and demonstrate its high activity in foliage of a C 3 tree where it rapidly integrates photosynthesis and C 1 metabolism contributing to new biomass via methyl transfer reactions, imparting a large natural 13 C-depleted signature. Using 13 CO 2 -labelling, we show that leaf serine, the S-methyl group of leaf methionine, pectin methyl esters, and the associated methanol released during cell wall expansion during growth, are directly produced from photosynthetically-linked C 1 metabolism, within minutes of light exposure. We speculate that the photosynthetic C 1 pathway is highly conserved across the photosynthetic tree of life, is responsible for synthesis of the greenhouse gas methane, and may have evolved with oxygenic photosynthesis by providing a mechanism of directly linking carbon and ammonia assimilation with growth. Although the rise in atmospheric CO 2 inhibits major metabolic pathways like photorespiration, our results suggest that the photosynthetic C 1 pathway may accelerate and represents a missing link between enhanced photosynthesis and plant growth rates during CO 2 fertilization under a changing climate., (© 2024. The Author(s).)

Day respiration (R d ) is the metabolic, nonphotorespiratory process by which illuminated leaves liberate CO 2 during photosynthesis. R d is used routinely in photosynthetic models and is thus critical for calculations. However, metabolic details associated with R d are poorly known, and this can be problematic to predict how R d changes with environmental conditions and relates to night respiration. It is often assumed that day respiratory CO 2 release just reflects 'ordinary' catabolism (glycolysis and Krebs 'cycle'). Here, we carried out a pulse-chase experiment, whereby a 13 CO 2 pulse in the light was followed by a chase period in darkness and then in the light. We took advantage of nontargeted, isotope-assisted metabolomics to determine non-'ordinary' metabolism, detect carbon remobilisation and compare light and dark 13 C utilisation. We found that several concurrent metabolic pathways ('ordinary' catabolism, oxidative pentose phosphates pathway, amino acid production, nucleotide biosynthesis and secondary metabolism) took place in the light and participated in net CO 2 efflux associated with day respiration. Flux reconstruction from metabolomics leads to an underestimation of R d , further suggesting the contribution of a variety of CO 2 -evolving processes. Also, the cornerstone of the Krebs 'cycle', citrate, is synthetised de novo from photosynthates mostly in darkness, and remobilised or synthesised from stored material in the light. Collectively, our data provides direct evidence that leaf day respiration (i) involves several CO 2 -producing reactions and (ii) is fed by different carbon sources, including stored carbon disconnected from current photosynthates., (© 2024 The Authors. Plant, Cell & Environment published by John Wiley & Sons Ltd.)

Our ability to predict temperature responses of leaf respiration in light and darkness (R L and R Dk ) is essential to models of global carbon dynamics. While many models rely on constant thermal sensitivity (characterized by Q 10 ), uncertainty remains as to whether Q 10 of R L and R Dk are actually similar. We measured short-term temperature responses of R L and R Dk in immature and mature leaves of two evergreen tree species, Castanopsis carlesii and Ormosia henry in an open field. R L was estimated by the Kok method, the Yin method and a newly developed Kok-iterC c method. When estimated by the Yin and Kok-iterC c methods, R L and R Dk had similar Q 10 (c. 2.5). The Kok method overestimated both Q 10 and the light inhibition of respiration. R L /R Dk was not affected by leaf temperature. Acclimation of respiration in summer was associated with a decline in basal respiration but not in Q 10 in both species, which was related to changes in leaf nitrogen content between seasons. Q 10 of R L and R Dk in mature leaves were 40% higher than in immature leaves. Our results suggest similar Q 10 values can be used to model R L and R Dk while leaf development-associated changes in Q 10 require special consideration in future respiration models., (© 2023 The Authors New Phytologist © 2023 New Phytologist Foundation.)

Evaluating leaf day respiration rate (RL), which is believed to differ from that in the dark (RDk), is essential for predicting global carbon cycles under climate change. Several studies have suggested that atmospheric CO2 impacts RL. However, the magnitude of such an impact and associated mechanisms remain uncertain. To explore the CO2 effect on RL, wheat (Triticum aestivum) and sunflower (Helianthus annuus) plants were grown under ambient (410 ppm) and elevated (820 ppm) CO2 mole fraction ([CO2]). RL was estimated from combined gas exchange and chlorophyll fluorescence measurements using the Kok method, the Kok-Phi method, and a revised Kok method (Kok-Cc method). We found that elevated growth [CO2] led to an 8.4% reduction in RL and a 16.2% reduction in RDk in both species, in parallel to decreased leaf N and chlorophyll contents at elevated growth [CO2]. We also looked at short-term CO2 effects during gas exchange experiments. Increased RL or RL/RDk at elevated measurement [CO2] were found using the Kok and Kok-Phi methods, but not with the Kok-Cc method. This discrepancy was attributed to the unaccounted changes in Cc in the former methods. We found that the Kok and Kok-Phi methods underestimate RL and overestimate the inhibition of respiration under low irradiance conditions of the Kok curve, and the inhibition of RL was only 6%, representing 26% of the apparent Kok effect. We found no significant long-term CO2 effect on RL/RDk, originating from a concurrent reduction in RL and RDk at elevated growth [CO2], and likely mediated by acclimation of nitrogen metabolism., Competing Interests: Conflict of interest statement. None declared., (© American Society of Plant Biologists 2022. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com.)

C 4 photosynthesis involves a series of biochemical and anatomical traits that significantly improve plant productivity under conditions that reduce the efficiency of C 3 photosynthesis. We explore how evolution of the three classical biochemical types of C 4 photosynthesis (NADP-ME, NAD-ME and PCK types) has affected the functions and properties of mitochondria. Mitochondria in C 4 NAD-ME and PCK types play a direct role in decarboxylation of metabolites for C 4 photosynthesis. Mitochondria in C 4 PCK type also provide ATP for C 4 metabolism, although this role for ATP provision is not seen in NAD-ME type. Such involvement has increased mitochondrial abundance/size and associated enzymatic capacity, led to changes in mitochondrial location and ultrastructure, and altered the role of mitochondria in cellular carbon metabolism in the NAD-ME and PCK types. By contrast, these changes in mitochondrial properties are absent in the C 4 NADP-ME type and C 3 leaves, where mitochondria play no direct role in photosynthesis. From an eco-physiological perspective, rates of leaf respiration in darkness vary considerably among C 4 species but does not differ systematically among the three C 4 types. This review outlines further mitochondrial research in key areas central to the engineering of the C 4 pathway into C 3 plants and to the understanding of variation in rates of C 4 dark respiration., (© 2021 The Authors. New Phytologist © 2021 New Phytologist Foundation.)

The prevalence of phylogenetic constraints in Rubisco evolution has been emphasised recently by (Bouvier et al., 2021), who argued that phylogenetic inheritance limits Rubisco adaptation much more than the biochemical trade-off between specificity, CO 2 affinity and turn-over. In this Opinion, we have critically examined how a phylogenetic signal can be computed with Rubisco kinetic properties and phylogenetic trees, and we arrive at a different conclusion. In particular, Rubisco's adaptation is partly driven by C 4 vs. C 3 photosynthetic conditions in Angiosperms, apparent phylogenetic signals being mostly due to either homoplasy, computation artefacts or the use of nearly identical sister species. While phylogenetic inheritance of an ancestral enzyme form probably has some role in Rubisco's adaptation landscape, it is a minor player, at least compared to microenvironmental conditions such as CO 2 and O 2 concentrations., (Copyright © 2021 Elsevier GmbH. All rights reserved.)

Leaf protein synthesis is an essential process at the heart of plant nitrogen (N) homeostasis and turnover that preferentially takes place in the light, that is, when N and CO 2 fixation occur. The carbon allocation to protein synthesis in illuminated leaves generally accounts for ca. 1 % of net photosynthesis. It is likely that protein synthesis activity varies with photosynthetic conditions (CO 2 /O 2 atmosphere composition) since changes in photorespiration and carbon provision should in principle impact on amino acid supply as well as metabolic regulation via leaf sugar content. However, possible changes in protein synthesis and translation activity when gaseous conditions vary are virtually unknown. Here, we address this question using metabolomics, isotopic techniques, phosphoproteomics and polysome quantitation, under different photosynthetic conditions that were varied with atmospheric CO 2 and O 2 mole fraction, using illuminated Arabidopsis rosettes under controlled gas exchange conditions. We show that carbon allocation to proteins is within 1-2.5 % of net photosynthesis, increases with photosynthesis rate and is unrelated to total amino acid content. In addition, photosynthesis correlates to polysome abundance and phosphorylation of ribosomal proteins and translation initiation factors. Our results demonstrate that translation activity follows photosynthetic activity, showing the considerable impact of metabolism (carboxylation-oxygenation balance) on protein synthesis., (Copyright © 2019 Elsevier B.V. All rights reserved.)

Net photosynthetic assimilation in C 3 plants is mostly viewed as a simple balance between CO 2 fixation by Rubisco-catalyzed carboxylation and CO 2 production by photorespiration (and to a lower extent, by day respiration) that can be easily manipulated during gas exchange experiments using the CO 2  : O 2 ratio of the environment. However, it now becomes clear that it is not so simple, because the photosynthetic response to gaseous conditions involves 'ancillary' metabolisms, even in the short-term. That is, carbon and nitrogen utilization by pathways other than the Calvin cycle and the photorespiratory cycle, as well as rapid signaling events, can influence the observed rate of net photosynthesis. The potential impact of such ancillary metabolisms is assessed as well as how it must be taken into account to avoid misinterpretation of photosynthetic CO 2 response curves or low O 2 effects in C 3 leaves., (© 2019 The Authors. New Phytologist © 2019 New Phytologist Trust.)

In gas-exchange experiments, manipulating CO 2 and O 2 is commonly used to change the balance between carboxylation and oxygenation. Downstream metabolism (utilization of photosynthetic and photorespiratory products) may also be affected by gaseous conditions but this is not well documented. Here, we took advantage of sunflower as a model species, which accumulates chlorogenate in addition to sugars and amino acids (glutamate, alanine, glycine and serine). We performed isotopic labelling with 13 CO 2 under different CO 2 /O 2 conditions, and determined 13 C contents to compute 13 C-allocation patterns and build-up rates. The 13 C content in major metabolites was not found to be a constant proportion of net fixed carbon but, rather, changed dramatically with CO 2 and O 2 . Alanine typically accumulated at low O 2 (hypoxic response) while photorespiratory intermediates accumulated under ambient conditions and at high photorespiration, glycerate accumulation exceeding serine and glycine build-up. Chlorogenate synthesis was relatively more important under normal conditions and at high CO 2 and its synthesis was driven by phosphoenolpyruvate de novo synthesis. These findings demonstrate that carbon allocation to metabolites other than photosynthetic end products is affected by gaseous conditions and therefore the photosynthetic yield of net nitrogen assimilation varies, being minimal at high CO 2 and maximal at high O 2 ., (© 2018 The Authors. New Phytologist © 2018 New Phytologist Trust.)

Cold nights impact grapevine flower development and fruit set. Regulation at the female meiosis stepmay be of considerable importance for further understanding on how flower reacts to cold stress. In this study, the impact of chilling temperature (0 °C overnight) on carbon metabolism was investigated in the inflorescencesof two cultivars, Pinot noir (Pinot) and Gewurztraminer (Gewurtz.). Fluctuations in photosynthetic activity and carbohydrate metabolism were monitored by analyzing gas exchanges, simultaneous photosystem I and II activities, andcarbohydrate content. Further, the expression of PEPc, PC, FNR, ISO, OXO, AGPase, amylases and invertase genes, activities of various enzymes, as well as metabolomic analysis were attained. Results showed that the chilling night has different impacts depending on cultivars. Thus, in Gewurtz., net photosynthesis (Pn) was transiently increased whereas, in Pinot, the Pn increase was persistent and concomitant with an inhibition of respiration. However, during the days following the cold night, photosynthetic activity was decreased, and the cyclic electron flow was inhibited in Gewurtz., suggesting lower efficient energy dissipation. Likewise, metabolomic analysis revealed that several metabolites contents (namely alanine, GABA, lysine and succinate)were distinctly modulated in the two cultivars. Taking together, these results reflect a photosynthetic metabolism alteration or internal CO2 conductance in Gewurtz. explaining partly why Pinot is less susceptible to cold stress., (Copyright © 2015 Elsevier Ireland Ltd. All rights reserved.)

Cellulose is one of the most important organic compounds in terrestrial ecosystems and represents a major plant structural polymer. However, knowledge of the regulation of cellulose biosynthesis is still rather limited. Recent studies have shown that the phosphorylation of cellulose synthases (CESAs) may represent a key regulatory event in cellulose production. However, the impact of environmental conditions on the carbon flux of cellulose deposition and on phosphorylation levels of CESAs has not been fully elucidated. Here, we took advantage of gas exchange measurements, isotopic techniques, metabolomics, and quantitative phosphoproteomics to investigate the regulation of cellulose production in Arabidopsis rosette leaves in different photosynthetic contexts (different CO2 mole fractions) or upon light/dark transition. We show that the carbon flux to cellulose production increased with photosynthesis, but not proportionally. The phosphorylation level of several phosphopeptides associated with CESA1 and 3, and several enzymes of sugar metabolism was higher in the light and/or increased with photosynthesis. By contrast, a phosphopeptide (Ser126) associated with CESA5 seemed to be more phosphorylated in the dark. Our data suggest that photosynthetic activity affects cellulose deposition through the control of both sucrose metabolism and cellulose synthesis complexes themselves by protein phosphorylation., (© The Author 2014. Published by Oxford University Press on behalf of the Society for Experimental Biology. All rights reserved. For permissions, please email: journals.permissions@oup.com.)

Photosynthetic CO2 assimilation is the carbon source for plant anabolism, including amino acid production and protein synthesis. The biosynthesis of leaf proteins is known for decades to correlate with photosynthetic activity but the mechanisms controlling this effect are not documented. The cornerstone of the regulation of protein synthesis is believed to be translation initiation, which involves multiple phosphorylation events in Eukaryotes. We took advantage of phosphoproteomic methods applied to Arabidopsis thaliana rosettes harvested under controlled photosynthetic gas-exchange conditions to characterize the phosphorylation pattern of ribosomal proteins (RPs) and eukaryotic initiation factors (eIFs). The analyses detected 14 and 11 new RP and eIF phosphorylation sites, respectively, revealed significant CO2-dependent and/or light/dark phosphorylation patterns and showed concerted changes in 13 eIF phosphorylation sites and 9 ribosomal phosphorylation sites. In addition to the well-recognized role of the ribosomal small subunit protein RPS6, our data indicate the involvement of eIF3, eIF4A, eIF4B, eIF4G and eIF5 phosphorylation in controlling translation initiation when photosynthesis varies. The response of protein biosynthesis to the photosynthetic input thus appears to be the result of a complex regulation network involving both stimulating (e.g. RPS6, eIF4B phosphorylation) and inhibiting (e.g. eIF4G phosphorylation) molecular events.

Leaf respiration is a major metabolic process that drives energy production and growth. Earlier works in this field were focused on the measurement of respiration rates in relation to carbohydrate content, photosynthesis, enzymatic activities or nitrogen content. Recently, several studies have shed light on the mechanisms describing the regulation of respiration in the light and in the dark and on associated metabolic flux patterns. This review will highlight advances made into characterizing respiratory fluxes and provide a discussion of metabolic respiration dynamics in relation to important biological functions., (Copyright © 2011 Elsevier Ltd. All rights reserved.)

Leaf intrinsic water-use efficiency (WUE), the ratio of photosynthetic rate to stomatal conductance (A/g(s) ), is a key plant trait linking terrestrial carbon and water cycles. A rapid, integrative proxy for A/g(s) is of benefit to crop breeding programmes aiming to improve WUE, but also for ecologists interested in plant carbon-water balance in natural systems. We hypothesize that the carbon isotope composition of leaf-respired CO(2) (δ(13) C(Rl) ), two hours after leaves are transferred to the dark, records photosynthetic carbon isotope discrimination and so provides a proxy for A/g(s) . To test this hypothesis, δ(13) C(Rl) was measured in four barley cultivars grown in the field at two levels of water availability and compared to leaf-level gas exchange (the ratio of leaf intercellular to ambient CO(2) partial pressure, C(i) /C(a) , and A/g(s) ). Leaf-respired CO(2) was more (13) C-depleted in plants grown at higher water availability, varied between days as environmental conditions changed, and was significantly different between cultivars. A strong relationship between δ(13) C(Rl) and δ(13) C of sucrose was observed. δ(13) C(Rl) was converted into apparent photosynthetic discrimination (Δ(13) C(Rl) ) revealing strong relationships between Δ(13) C(Rl) and C(i) /C(a) and A/g(s) during the vegetative stage of growth. We therefore conclude that δ(13) C(Rl) may provide a rapid, integrative proxy for A/g(s) in barley., (© 2011 Blackwell Publishing Ltd.)

Intense efforts are currently devoted to elucidate the metabolic networks of plants, in which nitrogen assimilation is of particular importance because it is strongly related to plant growth. In addition, at the leaf level, primary nitrogen metabolism interacts with photosynthesis, day respiration, and photorespiration, simply because nitrogen assimilation needs energy, reductant, and carbon skeletons which are provided by these processes. While some recent studies have focused on metabolomics and genomics of plant leaves, the actual metabolic fluxes associated with nitrogen metabolism operating in leaves are not very well known. In the present paper, it is emphasized that (12)C/(13)C and (14)N/(15)N stable isotopes have proved to be useful tools to investigate such metabolic fluxes and isotopic data are reviewed in the light of some recent advances in this area. Although the potential of stable isotopes remains high, it is somewhat limited by our knowledge of some isotope effects associated with enzymatic reactions. Therefore, this paper should be viewed as a call for more fundamental studies on isotope effects by plant enzymes.

Discrimination against 13C during photosynthesis is a well-characterised phenomenon. It leaves behind distinct signatures in organic matter of plants and in the atmosphere. The former is depleted in 13C, the latter is enriched during periods of preponderant photosynthetic activity of terrestrial ecosystems. The intra-annual cycle and latitudinal gradient in atmospheric 13C resulting from photosynthetic and respiratory activities of terrestrial plants have been exploited for the reconstruction of sources and sinks through deconvolution by inverse modelling. Here, we compile evidence for widespread post-photosynthetic fractionation that further modifies the isotopic signatures of individual plant organs and consequently leads to consistent differences in delta13C between plant organs. Leaves were on average 0.96 per thousand and 1.91 per thousand more depleted than roots and woody stems, respectively. This phenomenon is relevant if the isotopic signature of CO2-exchange fluxes at the ecosystem level is used for the reconstruction of individual sources and sinks. It may also modify the parameterization of inverse modelling approaches if it leads to different isotopic signatures of organic matter with different residence times within the ecosystems and to a respiratory contribution to the average difference between the isotopic composition of plant organic matter and the atmosphere. We discuss the main hypotheses that can explain the observed inter-organ differences in delta13C., (Copyright 2005 John Wiley & Sons, Ltd)

Rubisco activase ( RCA) is an ancillary photosynthetic protein essential for Rubisco activity. Some data suggest that post-translational modifications (such as reduction of disulphide bridges) are involved in the regulation of RCA activity. However, despite the key role of protein phosphorylation in general metabolic regulation, RCA phosphorylation has not been well characterised. We took advantage of phosphoproteomics and gas exchange analyses with instant sampling adapted to Arabidopsis rosettes to examine the occurrence and variations of phosphopeptides associated with RCA in different photosynthetic contexts ( CO2 mole fraction, light and dark). We detected two phosphopeptides from RCA corresponding to residues Thr 78 and Ser 172, and show that the former is considerably more phosphorylated in the dark than in the light, while the latter show no light/dark pattern. The CO2 mole fraction did not influence phosphorylation of either residue. Phosphorylation thus appears to be a potential mechanism associated with RCA dark inactivation, when Rubisco-catalysed carboxylation is arrested. Since Thr 78 and Ser 172 are located in the N and Walker domains of the protein, respectively, the involvement of phosphorylation in protein-protein interaction and catalysis is likely. [ABSTRACT FROM AUTHOR]