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Sharkey TD. The end game(s) of photosynthetic carbon metabolism. PLANT PHYSIOLOGY 2024; 195:67-78. [PMID: 38163636 PMCID: PMC11060661 DOI: 10.1093/plphys/kiad601] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/18/2023] [Accepted: 10/27/2023] [Indexed: 01/03/2024]
Abstract
The year 2024 marks 70 years since the general outline of the carbon pathway in photosynthesis was published. Although several alternative pathways are now known, it is remarkable how many organisms use the reaction sequence described 70 yrs ago, which is now known as the Calvin-Benson cycle or variants such as the Calvin-Benson-Bassham cycle or Benson-Calvin cycle. However, once the carbon has entered the Calvin-Benson cycle and is converted to a 3-carbon sugar, it has many potential fates. This review will examine the last stages of photosynthetic metabolism in leaves. In land plants, this process mostly involves the production of sucrose provided by an endosymbiont (the chloroplast) to its host for use and transport to the rest of the plant. Photosynthetic metabolism also usually involves the synthesis of starch, which helps maintain respiration in the dark and enables the symbiont to supply sugars during both the day and night. Other end products made in the chloroplast are closely tied to photosynthetic CO2 assimilation. These include serine from photorespiration and various amino acids, fatty acids, isoprenoids, and shikimate pathway products. I also describe 2 pathways that can short circuit parts of the Calvin-Benson cycle. These final processes of photosynthetic metabolism play many important roles in plants.
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Affiliation(s)
- Thomas D Sharkey
- MSU-DOE Plant Research Laboratory, Plant Resilience Institute, and Department of Biochemistry and Molecular Biology, Michigan State University, East Lansing, MI 48824, USA
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Scharte J, Hassa S, Herrfurth C, Feussner I, Forlani G, Weis E, von Schaewen A. Metabolic priming in G6PDH isoenzyme-replaced tobacco lines improves stress tolerance and seed yields via altering assimilate partitioning. THE PLANT JOURNAL : FOR CELL AND MOLECULAR BIOLOGY 2023; 116:1696-1716. [PMID: 37713307 DOI: 10.1111/tpj.16460] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/09/2023] [Revised: 08/25/2023] [Accepted: 08/29/2023] [Indexed: 09/17/2023]
Abstract
We investigated the basis for better performance of transgenic Nicotiana tabacum plants with G6PDH-isoenzyme replacement in the cytosol (Xanthi::cP2::cytRNAi, Scharte et al., 2009). After six generations of selfing, infiltration of Phytophthora nicotianae zoospores into source leaves confirmed that defence responses (ROS, callose) are accelerated, showing as fast cell death of the infected tissue. Yet, stress-related hormone profiles resembled susceptible Xanthi and not resistant cultivar SNN, hinting at mainly metabolic adjustments in the transgenic lines. Leaves of non-stressed plants contained twofold elevated fructose-2,6-bisphosphate (F2,6P2 ) levels, leading to partial sugar retention (soluble sugars, starch) and elevated hexose-to-sucrose ratios, but also more lipids. Above-ground biomass lay in between susceptible Xanthi and resistant SNN, with photo-assimilates preferentially allocated to inflorescences. Seeds were heavier with higher lipid-to-carbohydrate ratios, resulting in increased harvest yields - also under water limitation. Abiotic stress tolerance (salt, drought) was improved during germination, and in floated leaf disks of non-stressed plants. In leaves of salt-watered plants, proline accumulated to higher levels during illumination, concomitant with efficient NADP(H) use and recycling. Non-stressed plants showed enhanced PSII-induction kinetics (upon dark-light transition) with little differences at the stationary phase. Leaf exudates contained 10% less sucrose, similar amino acids, but more fatty acids - especially in the light. Export of specific fatty acids via the phloem may contribute to both, earlier flowering and higher seed yields of the Xanthi-cP2 lines. Apparently, metabolic priming by F2,6P2 -combined with sustained NADP(H) turnover-bypasses the genetically fixed growth-defence trade-off, rendering tobacco plants more stress-resilient and productive.
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Affiliation(s)
- Judith Scharte
- Institut für Biologie und Biotechnologie der Pflanzen, Fachbereich Biologie, Universität Münster, Schlossplatz 7, D-48149, Münster, Germany
| | - Sebastian Hassa
- Institut für Biologie und Biotechnologie der Pflanzen, Fachbereich Biologie, Universität Münster, Schlossplatz 7, D-48149, Münster, Germany
| | - Cornelia Herrfurth
- Albrecht-von-Haller-Institut für Pflanzenwissenschaften and Göttinger Zentrum für Molekulare Biowissenschaften (GZMB), Abteilung Biochemie der Pflanze, Universität Göttingen, Justus-von-Liebig-Weg 11, D-37077, Göttingen, Germany
| | - Ivo Feussner
- Albrecht-von-Haller-Institut für Pflanzenwissenschaften and Göttinger Zentrum für Molekulare Biowissenschaften (GZMB), Abteilung Biochemie der Pflanze, Universität Göttingen, Justus-von-Liebig-Weg 11, D-37077, Göttingen, Germany
| | - Giuseppe Forlani
- Laboratorio di Fisiologia e Biochimica Vegetale, Dipartimento di Scienze della Vita e Biotecnologie, Universitá degli Studi di Ferrara, Via L. Borsari 46, I-44121, Ferrara, Italy
| | - Engelbert Weis
- Institut für Biologie und Biotechnologie der Pflanzen, Fachbereich Biologie, Universität Münster, Schlossplatz 7, D-48149, Münster, Germany
| | - Antje von Schaewen
- Institut für Biologie und Biotechnologie der Pflanzen, Fachbereich Biologie, Universität Münster, Schlossplatz 7, D-48149, Münster, Germany
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Knebl A, Domes R, Yan D, Popp J, Trumbore S, Frosch T. Fiber-Enhanced Raman Gas Spectroscopy for 18O- 13C-Labeling Experiments. Anal Chem 2019; 91:7562-7569. [PMID: 31050402 DOI: 10.1021/acs.analchem.8b05684] [Citation(s) in RCA: 31] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
Abstract
Stable isotopes are used in ecology to track and disentangle different processes and pathways. Especially for studies focused on the gas exchange of plants, sensing techniques that offer oxygen (O2) and carbon dioxide (CO2) sensitivity with isotopic discrimination are highly sought after. Addressing this challenge, fiber-enhanced Raman gas spectroscopy is introduced as a fast optical technique directly combining 13CO2 and 12CO2 as well as 18O2 and 16O2 measurements in one instrument. We demonstrate how a new type of optical hollow-core fiber, the so-called revolver fiber, is utilized for enhanced Raman gas sensing. Carbon dioxide and oxygen isotopologues were measured at concentrations expected when using 13C- and 18O-labeled gases in plant experiments. Limits of detection have been determined to be 25 ppm for CO2 and 150 ppm for O2. The combination of measurements with different integration times allows the creation of highly resolved broadband spectra. With the help of calculations based on density functional theory, the line at 1512 cm-1 occurring in the oxygen spectrum is assigned to 18O16O. The relative abundances of the isotopologues 18O16O and nitrogen 15N14N were in good agreement with typical values. For CO2, fiber-enhanced Raman spectra show the Fermi diad and hotbands of 12C16O2, 13C16O2, and 12C18O16O. Several weak lines were observed, and the line at 1426 cm-1 was identified as originating from the (0 4 0 2) → (0 2 0 2) transition of 12C16O2. With the demonstrated sensitivity and discriminatory power, fiber-enhanced Raman spectroscopy is a possible alternative means to investigate plant metabolism, directly combining 13CO2 and 12CO2 measurements with 18O2 and 16O2 measurements in one instrument. The presented method thus has large potential for basic analytical investigations as well as for applications in the environmental sciences.
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Affiliation(s)
- Andreas Knebl
- Leibniz Institute of Photonic Technology , 07745 Jena , Germany.,Max-Planck-Institute for Biogeochemistry , 07745 Jena , Germany
| | - Robert Domes
- Leibniz Institute of Photonic Technology , 07745 Jena , Germany
| | - Di Yan
- Leibniz Institute of Photonic Technology , 07745 Jena , Germany
| | - Juergen Popp
- Leibniz Institute of Photonic Technology , 07745 Jena , Germany.,Institute of Physical Chemistry & Abbe Center of Photonics , Friedrich Schiller University , 07743 Jena , Germany
| | - Susan Trumbore
- Max-Planck-Institute for Biogeochemistry , 07745 Jena , Germany
| | - Torsten Frosch
- Leibniz Institute of Photonic Technology , 07745 Jena , Germany.,Institute of Physical Chemistry & Abbe Center of Photonics , Friedrich Schiller University , 07743 Jena , Germany
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Abstract
Photosynthesis is fundamental to biomass production, but is a dynamic process sensitive to environmental constraints. In recent years, approaches to increase biomass and grain yield by altering photosynthetically related processes in the plant have received considerable attention. However, improving biomass yield requires a predictive understanding of the molecular mechanisms that allow photosynthesis to be adjusted. The important roles of metabolic reactions external to those directly involved in photosynthesis are highlighted in this review; however, our major focus is on the routes taken to improve photosynthetic carbon assimilation and to increase photosynthetic efficiency and consequently biomass yield.
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