DOCSLIB.ORG

Photosynthesis Energy from the Sun! ! Use Light As an Energy Source for Making ATP (Light Reaction)

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Photosynthesis Energy from the Sun! ! Use Light As an Energy Source for Making ATP (Light Reaction) The Great Tree of Life ! "As buds give rise by growth to fresh buds, and these, if vigorous, branch out and overtop on all sides many a feebler branch, so by generation I believe it has been with the great Tree of Life, which fills with its dead and broken branches the crust of the earth, and covers the surface with its ever branching and beautiful ramifications." -- Charles Darwin, 1859 Origins ! Origins - How did life arise? ! “But if (and Oh! What a big if!) we could conceive in some warm little pond, with all sorts of ammonia and phosphoric salts, light, heat, electricity etc. …” Darwin, Letter to J. Hooker, 1871 1 “Prokaryotes” Organisms that run the world ! Dominant Life forms on Earth "10x the biomass of Eukaryotes "Extreme metabolic diversity "The basis for eukaryotic metabolism “Prokaryotes” Organisms that run the world ! Dominant Life forms on Earth "10x the biomass of Eukaryotes "Extreme metabolic diversity "The basis for eukaryotic metabolism ! Crucial for many global processes "Biogeochemical cycling "It’s a prokaryotic world. We need them, but they don’t need us! 2 “Prokaryotes” vs. Eukaryotes (Briefly) ! Unlike Eukaryotes, prokaryotes have "No nuclear envelope "No membrane bound organelles "Circular DNA, with relatively few genes “Prokaryotes” - Classification ! Formerly all prokaryotes lumped together 3 “Prokaryotes” - Classification ! Formerly all prokaryotes lumped together "Primitive similarities "“Prokaryotes” now considered to be __phyletic #United by primitive similarities ! Three domains of life Prokaryotes - Two Domains Bacteria Archaea Eukarya Organelles, nucleus Linear chromosomes Mitosis and meiosis LUCA(C) DNA/Proteins RNA, ribosomes Circular Chromosome RNA world? Abiogenesis 4 Swapping Genes Lateral (= Horizontal) Gene Transfer ! Unlike most Eukaryotes, “prokaryotes” can laterally transfer genes!!! "Very important for evolution ! Various mechanisms "E.g. transformation, transduction, conjugation. Know general phenomenon, not details The very early history of life 5 The very early history of life The very early history of life ! Earth forms about 4.5 bya ! Life appears “quickly”! ! Environment very different "Volcanoes "Meteor impacts "Very little oxygen ! Glycolysis a widespread and primitive pathway - Implies …? 6 Photosynthesis Energy from the sun! ! Use light as an energy source for making ATP (Light reaction) "O2 as a by-product (usually) ! Use ATP to create sugars from CO2 ! These are now photoautotrophs ! The oxygen revolution: "2.5 billion years ago "Good news, bad news The oxygen revolution: Good news, bad news ! Origin of cyanobacteria "Increased Oxygen levels (eventually) "Oxygen is very reactive - breaks bonds "Bad news for anaerobic organisms ! But, allowed the evolution of aerobic respiration! 7 Aerobic Respiration ! Much greater yield of ATP ! In some ways, the opposite of Photosynthesis "Photosynthesis: #ATP (from Light rxn) +CO2-> Sugar+O2 "Aerobic respiration: #Sugar+O2 -> ATP + CO2 Big Idea: Evolution is a tinkerer ! 1) Pathways for production of ATP in aerobic respiration apparently borrowed from (or at least shared with) photosynthesis! ! 2) Anaerobic origins of photosynthesis apparent even in modern plants "Enzymes used for fixing CO2 are interfered with by O2 - photorespiration "Photorespiration as an “evolutionary relic” 8 Summary ! “Prokaryotes” oldest, most diverse group "All combinations of energy, carbon sources ! Early Earth environment anaerobic "Only anaerobic glycolysis possible - low yield "Very widespread, apparently old ! Photosynthesis -> Oxygen revolution 2.5bya "Bad for anaerobes (major extinction!) "Allowed aerobic respiration!!! ! Big Idea: Evolution as tinkering 9.
Load more

Recommended publications
  • Bioinorganic Chemistry Content
    Bioinorganic Chemistry Content 1. What is bioinorganic chemistry? 2. Evolution of elements 3. Elements and molecules of life 4. Phylogeny 5. Metals in biochemistry 6. Ligands in biochemistry 7. Principals of coordination chemistry 8. Properties of bio molecules 9. Biochemistry of main group elements 10. Biochemistry of transition metals 11. Biochemistry of lanthanides and actinides 12. Modell complexes 13. Analytical methods in bioinorganic 14. Applications areas of bioinorganic chemistry "Simplicity is the ultimate sophistication" Leonardo Da Vinci Bioinorganic Chemistry Slide 1 Prof. Dr. Thomas Jüstel Literature • C. Elschenbroich, A. Salzer, Organometallchemie, 2. Auflage, Teubner, 1988 • S.J. Lippard, J.N. Berg, Bioinorganic Chemistry, Spektrum Akademischer Verlag, 1995 • J.E. Huheey, E. Keiter, R. Keiter, Anorganische Chemie – Prinzipien von Struktur und Reaktivität, 3. Auflage, Walter de Gruyter, 2003 • W. Kaim, B. Schwederski: Bioinorganic Chemistry, 4. Auflage, Vieweg-Teubner, 2005 • H. Rauchfuß, Chemische Evolution und der Ursprung des Lebens, Springer, 2005 • A.F. Hollemann, N. Wiberg, Lehrbuch der Anorganischen Chemie, 102. Auflage, de Gruyter, 2007 • I. Bertini, H.B. Gray, E.I. Stiefel, J.S. Valentine, Biological Chemistry, University Science Books, 2007 • N. Metzler-Nolte, U. Schatzschneier, Bioinorganic Chemistry: A Practical Course, Walter de Gruyter, 2009 • W. Ternes, Biochemie der Elemente, Springer, 2013 • D. Rabinovich, Bioinorganic Chemistry, Walter de Gruyter, 2020 Bioinorganic Chemistry Slide 2 Prof. Dr. Thomas Jüstel 1. What is Bioinorganic Chemistry? A Highly Interdisciplinary Science at the Verge of Biology, Chemistry, Physics, and Medicine Biochemistry Inorganic Chemistry (Micro)- Physics & Biology Spectroscopy Bioinorganic Chemistry Pharmacy & Medicine & Toxicology Physiology Diagnostics Bioinorganic Chemistry Slide 3 Prof. Dr. Thomas Jüstel 2. Evolution of the Elements Most Abundant Elements in the Universe According to Atomic Fraction Are: 1.
    [Show full text]
  • AP Biology Life’S Beginning on Earth According to Scientific Findings (Associated Learning Objectives: 1.9, 1.10, 1.11, 1.12, 1.27, 1.28, 1.29, 1.30, 1.31, and 1.32)
    AP Auburn University AP Summer Institute BIOLOGYJuly 11-14, 2016 AP Biology Life’s beginning on Earth according to scientific findings (Associated Learning Objectives: 1.9, 1.10, 1.11, 1.12, 1.27, 1.28, 1.29, 1.30, 1.31, and 1.32) I. The four steps necessary for life to emerge on Earth. (This is according to accepted scientific evidence.) A. First: An abiotic (non-living) synthesis of Amino Acids and Nucleic Acids must occur. 1. The RNA molecule is believed to have evolved first. It is not as molecularly stable as DNA though. 2. The Nucleic Acids (DNA or RNA) are essential for storing, retrieving, or conveying by inheritance molecular information on constructing the components of living cells.. 3. The Amino Acids, the building blocks of proteins, are needed to construct the “work horse” molecules of a cell. a. The majority of a cell or organism, in biomass (dry weight of an organism), is mostly protein. B. Second: Monomers must be able to join together to form more complex polymers using energy that is obtained from the surrounding environment. 1. Seen in monosaccharides (simple sugars) making polysaccharides (For energy storage or cell walls of plants.) 2. Seen in the making of phospholipids for cell membranes. 3. Seen in the making of messenger RNA used in making proteins using Amino Acids. 4. Seen in making chromosomes out of strings of DNA molecules. (For information storage.) C. Third: The RNA/DNA molecules form and gain the ability to reproduce and stabilize by using chemical bonds and complimentary bonding.
    [Show full text]
  • Plant Sulphur Metabolism Is Stimulated by Photorespiration
    ARTICLE https://doi.org/10.1038/s42003-019-0616-y OPEN Plant sulphur metabolism is stimulated by photorespiration Cyril Abadie1,2 & Guillaume Tcherkez 1* 1234567890():,; Intense efforts have been devoted to describe the biochemical pathway of plant sulphur (S) assimilation from sulphate. However, essential information on metabolic regulation of S assimilation is still lacking, such as possible interactions between S assimilation, photo- synthesis and photorespiration. In particular, does S assimilation scale with photosynthesis thus ensuring sufficient S provision for amino acids synthesis? This lack of knowledge is problematic because optimization of photosynthesis is a common target of crop breeding and furthermore, photosynthesis is stimulated by the inexorable increase in atmospheric CO2. Here, we used high-resolution 33S and 13C tracing technology with NMR and LC-MS to access direct measurement of metabolic fluxes in S assimilation, when photosynthesis and photorespiration are varied via the gaseous composition of the atmosphere (CO2,O2). We show that S assimilation is stimulated by photorespiratory metabolism and therefore, large photosynthetic fluxes appear to be detrimental to plant cell sulphur nutrition. 1 Research School of Biology, Australian National University, Canberra, ACT 2601, Australia. 2Present address: IRHS (Institut de Recherche en Horticulture et Semences), UMR 1345, INRA, Agrocampus-Ouest, Université d’Angers, SFR 4207 QuaSaV, 49071 Angers, Beaucouzé, France. *email: guillaume. [email protected] COMMUNICATIONS BIOLOGY
    [Show full text]
  • Photorespiration Pathways in a Chemolithoautotroph
    bioRxiv preprint doi: https://doi.org/10.1101/2020.05.08.083683; this version posted May 9, 2020. The copyright holder for this preprint (which was not certified by peer review) is the author/funder, who has granted bioRxiv a license to display the preprint in perpetuity. It is made available under aCC-BY-NC 4.0 International license. Photorespiration pathways in a chemolithoautotroph Nico J. Claassens*1, Giovanni Scarinci*1, Axel Fischer1, Avi I. Flamholz2, William Newell1, Stefan Frielingsdorf3, Oliver Lenz3, Arren Bar-Even†1 1Max Planck Institute of Molecular Plant Physiology, Am Mühlenberg 1, 14476 Potsdam-Golm, Germany 2Department of Molecular and Cell Biology, University of California, Berkeley, California 94720, United States. 3Institut für Chemie, Physikalische Chemie, Technische Universität Berlin, Strasse des 17. Juni 135, 10623 Berlin, Germany †corresponding author; phone: +49 331 567-8910; Email: [email protected] *contributed equally Key words: CO2 fixation; hydrogen-oxidizing bacteria; glyoxylate shunt; malate synthase; oxalate metabolism 1 bioRxiv preprint doi: https://doi.org/10.1101/2020.05.08.083683; this version posted May 9, 2020. The copyright holder for this preprint (which was not certified by peer review) is the author/funder, who has granted bioRxiv a license to display the preprint in perpetuity. It is made available under aCC-BY-NC 4.0 International license. Abstract Carbon fixation via the Calvin cycle is constrained by the side activity of Rubisco with dioxygen, generating 2-phosphoglycolate. The metabolic recycling of 2-phosphoglycolate, an essential process termed photorespiration, was extensively studied in photoautotrophic organisms, including plants, algae, and cyanobacteria, but remains uncharacterized in chemolithoautotrophic bacteria.
    [Show full text]
  • Mass Fractionation Laws, Mass-Independent Effects, and Isotopic Anomalies Nicolas Dauphas and Edwin A
    EA44CH26-Dauphas ARI 10 June 2016 9:41 ANNUAL REVIEWS Further Click here to view this article's online features: • Download figures as PPT slides • Navigate linked references • Download citations Mass Fractionation Laws, • Explore related articles • Search keywords Mass-Independent Effects, and Isotopic Anomalies Nicolas Dauphas1,∗ and Edwin A. Schauble2 1Origins Laboratory, Department of the Geophysical Sciences and Enrico Fermi Institute, The University of Chicago, Chicago, Illinois 60637; email: [email protected] 2Department of Earth and Space Sciences, University of California, Los Angeles, California 90095 Annu. Rev. Earth Planet. Sci. 2016. 44:709–83 Keywords First published online as a Review in Advance on isotopes, fractionation, laws, NFS, nuclear, anomalies, nucleosynthesis, May 18, 2016 meteorites, planets The Annual Review of Earth and Planetary Sciences is online at earth.annualreviews.org Abstract This article’s doi: Isotopic variations usually follow mass-dependent fractionation, meaning 10.1146/annurev-earth-060115-012157 that the relative variations in isotopic ratios scale with the difference in Copyright c 2016 by Annual Reviews. mass of the isotopes involved (e.g., δ17O ≈ 0.5 × δ18O). In detail, how- All rights reserved ever, the mass dependence of isotopic variations is not always the same, ∗ Corresponding author and different natural processes can define distinct slopes in three-isotope diagrams. These variations are subtle, but improvements in analytical capa- Access provided by University of Chicago Libraries on 07/19/16. For personal use only. Annu. Rev. Earth Planet. Sci. 2016.44:709-783. Downloaded from www.annualreviews.org bilities now allow precise measurement of these effects and make it possi- ble to draw inferences about the natural processes that caused them (e.g., reaction kinetics versus equilibrium isotope exchange).
    [Show full text]
  • Transport Proteins Enabling Plant Photorespiratory Metabolism
    plants Review Transport Proteins Enabling Plant Photorespiratory Metabolism Franziska Kuhnert, Urte Schlüter, Nicole Linka and Marion Eisenhut * Institute of Plant Biochemistry, Cluster of Excellence on Plant Science (CEPLAS), Heinrich Heine University Düsseldorf, Universitätsstrasse 1, 40225 Düsseldorf, Germany; [email protected] (F.K.); [email protected] (U.S.); [email protected] (N.L.) * Correspondence: [email protected]; Tel.: +49-211-8110467 Abstract: Photorespiration (PR) is a metabolic repair pathway that acts in oxygenic photosynthetic organisms to degrade a toxic product of oxygen fixation generated by the enzyme ribulose 1,5- bisphosphate carboxylase/oxygenase. Within the metabolic pathway, energy is consumed and carbon dioxide released. Consequently, PR is seen as a wasteful process making it a promising target for engineering to enhance plant productivity. Transport and channel proteins connect the organelles accomplishing the PR pathway—chloroplast, peroxisome, and mitochondrion—and thus enable efficient flux of PR metabolites. Although the pathway and the enzymes catalyzing the biochemical reactions have been the focus of research for the last several decades, the knowledge about transport proteins involved in PR is still limited. This review presents a timely state of knowledge with regard to metabolite channeling in PR and the participating proteins. The significance of transporters for implementation of synthetic bypasses to PR is highlighted. As an excursion, the physiological contribution of transport proteins that are involved in C4 metabolism is discussed. Keywords: photorespiration; photosynthesis; transport protein; plant; Rubisco; metabolite; synthetic bypass; C4 photosynthesis Citation: Kuhnert, F.; Schlüter, U.; Linka, N.; Eisenhut, M. Transport Proteins Enabling Plant Photorespiratory Metabolism. Plants 1. Introduction—The Photorespiratory Metabolism 2021, 10, 880.
    [Show full text]
  • Israel Zelitch
    Israel Zelitch Photosynthesis Research 67: 157–176, 2001. 159 © 2001 Kluwer Academic Publishers. Printed in the Netherlands. Personal perspective/Historical corner Travels in a world of small science∗ Israel Zelitch Department of Biochemistry and Genetics, The Connecticut Agricultural Experiment Station, P.O. Box 1106, New Haven, CT 06504, USA Received 1 January 2001; accepted in revised form 26 January 2001 Key words: Robert H. Burris, carbon dioxide assimilation, catalase, glycolate, glyoxylate, James G. Horsfall, Severo Ochoa, photorespiration Abstract As a boy, I read Sinclair Lewis’s Arrowsmith and dreamed of doing research of potential benefit to society. I describe the paths of my scientific career that followed. Several distinguished scientists served as my mentors and I present their profiles. Much of my career was in a small department at a small institution where independent researchers collaborated informally. I describe the unique method of carrying on research there. My curiosity about glycolate metabolism led to unraveling the enzymatic mechanism of the glycolate oxidase reaction and showing the importance of H2O2 as a byproduct. I discovered enzymes catalyzing the reduction of glyoxylate and hydroxypyruvate. I found α-hydroxysulfonates were useful competitive inhibitors of glycolate oxidase. In a moment of revelation, I realized that glycolate metabolism was an essential part of photorespiration, a process that lowers net photosynthesis in C3 plants. I added inhibitors of glycolate oxidase to leaves and showed: (1) glycolate was synthesized only in light as an early product of photosynthetic CO2 assimilation, (2) the rate of glycolate oxidation consumed a sizable fraction of net photosynthesis in C3 but not in C4 plants, and (3) that glycolate metabolism increased greatly at higher temperatures.
    [Show full text]
  • BIOLOGY CLASS X Teacher Resource
    BIOLOGY CLASS X Teacher Resource 1 Team Lead: Umme Farwah Halai Subject Specialist: Saima Pervaiz Reviewer: Muhammad Waseem Ahmed Disclaimer The web based resources are reference materials for teachers. They have been compiled under the supervision of the Ziauddin College of Education for Ziauddin’s Examination Board. 2 GRADE 10 Weightage Sections Chapters in Evaluation Biodiversity Section 1 Biodiversity 03 % Enzymes Section 2 Cell Biology 12 % Bioenergetics Homeostasis Coordination 20 % Section 3 Life Processes Support and Movement Inheritance 14 % Section 4 Continuity in Life Biotechnology 08 % Section 5 Application of Pharmacology Biology SECTION 1 : BIODIVERSITY 3 SUB TOPICS STUDENT LEARNING OUTCOMES REFERENCE MATERIAL CHAPTER Definition and UNDERSTSANDING Introduction of 3 Define biodiversity. Biodiversity Describe the basis of classification of Aims and Principles of Classification living organisms. History of Explain the aims and principles of classification, keeping in view its Classification Systems historical background. Five-Kingdom Explain the basis for establishing 5 Classification System kingdoms. Conservation of Describe the major variety of life on the Biodiversity planet earth. Define the concept of conservation. Explain the impact of human beings on biodiversity. Identify causes of deforestation and its effects on biodiversity. Describe some of the issues of conservation in Pakistan (especially with regard to deforestation and hunting). SKILLS Examine some living or preserved plants and animals. Classify representative
    [Show full text]
  • A Cyanobacterial Photorespiratory Bypass Model to Enhance
    www.nature.com/scientificreports OPEN A cyanobacterial photorespiratory bypass model to enhance photosynthesis by rerouting photorespiratory pathway in ­C3 plants Ghazal Khurshid1,2, Anum Zeb Abbassi1, Muhammad Farhan Khalid2, Mahnoor Naseer Gondal2, Tatheer Alam Naqvi1, Mohammad Maroof Shah1, Safee Ullah Chaudhary2* & Raza Ahmad1* Plants employ photosynthesis to produce sugars for supporting their growth. During photosynthesis, an enzyme Ribulose 1,5 bisphosphate carboxylase/oxygenase (Rubisco) combines its substrate Ribulose 1,5 bisphosphate (RuBP) with CO2 to produce phosphoglycerate (PGA). Alongside, Rubisco also takes up O2 and produce 2-phosphoglycolate (2-PG), a toxic compound broken down into PGA through photorespiration. Photorespiration is not only a resource-demanding process but also results in CO2 loss which afects photosynthetic efciency in C3 plants. Here, we propose to circumvent photorespiration by adopting the cyanobacterial glycolate decarboxylation pathway into C3 plants. For that, we have integrated the cyanobacterial glycolate decarboxylation pathway into a kinetic model of C3 photosynthetic pathway to evaluate its impact on photosynthesis and photorespiration. Our results show that the cyanobacterial glycolate decarboxylation bypass model exhibits a 10% increase in net photosynthetic rate (A) in comparison with C3 model. Moreover, an increased supply of intercellular CO2 (Ci) from the bypass resulted in a 54.8% increase in PGA while reducing photorespiratory intermediates including glycolate (− 49%) and serine (− 32%). The bypass model, at default conditions, also elucidated a decline in phosphate-based metabolites including RuBP (− 61.3%). The C3 model at elevated level of inorganic phosphate (Pi), exhibited a signifcant change in RuBP (+ 355%) and PGA (− 98%) which is attributable to the low availability of Ci.
    [Show full text]
  • Magnesium–Isotope Fractionation in Chlorophyll-A Extracted from Two Plants with Different Pathways of Carbon Fixation (C3, C4)
    molecules Article Magnesium–Isotope Fractionation in Chlorophyll-a Extracted from Two Plants with Different Pathways of Carbon Fixation (C3, C4) Katarzyna Wrobel 1,2,* , Jakub Karasi ´nski 1 , Andrii Tupys 1, Missael Antonio Arroyo Negrete 2, Ludwik Halicz 1,3, Kazimierz Wrobel 2 and Ewa Bulska 1,* 1 Faculty of Chemistry, Biological and Chemical Research Centre, University of Warsaw, Zwirki i Wigury 101, 02-093 Warszawa, Poland; [email protected] (J.K.); [email protected] (A.T.); [email protected] (L.H.) 2 Chemistry Department, University of Guanajuato, L. de Retana 5, 36000 Guanajuato, Mexico; [email protected] (M.A.A.N.); [email protected] (K.W.) 3 Geological Survey of Israel, 32 Y. Leybowitz st., 9692100 Jerusalem, Israel * Correspondence: [email protected] (K.W.); [email protected] (E.B.); Tel.: +52-473-732-7555 (K.W.); +48-22-552-6522 (E.B.) Academic Editors: Zikri Arslan and James Barker Received: 26 February 2020; Accepted: 31 March 2020; Published: 3 April 2020 Abstract: Relatively few studies have been focused so far on magnesium–isotope fractionation during plant growth, element uptake from soil, root-to-leaves transport and during chlorophylls biosynthesis. In this work, maize and garden cress were hydroponically grown in identical conditions in order to examine if the carbon fixation pathway (C4, C3, respectively) might have impact on Mg-isotope fractionation in chlorophyll-a. The pigment was purified from plants extracts by preparative reversed phase chromatography, and its identity was confirmed by high-resolution mass spectrometry. The green parts of plants and chlorophyll-a fractions were acid-digested and submitted to ion chromatography coupled through desolvation system to multiple collector inductively coupled plasma-mass spectrometry.
    [Show full text]
  • A Photoionization Mass Spectrometry Investigation Into Complex Organic
    The Astrophysical Journal, 916:74 (12pp), 2021 August 1 https://doi.org/10.3847/1538-4357/ac0537 © 2021. The American Astronomical Society. All rights reserved. A Photoionization Mass Spectrometry Investigation into Complex Organic Molecules Formed in Interstellar Analog Ices of Carbon Monoxide and Water Exposed to Ionizing Radiation Andrew M. Turner1,2, Alexandre Bergantini1,2 , Andreas S. Koutsogiannis1,2, N. Fabian Kleimeier1,2, Santosh K. Singh1,2, Cheng Zhu1,2 , André K. Eckhardt3 , and Ralf I. Kaiser1,2 1 Department of Chemistry, University of Hawaii at Manoa, Honolulu, HI 96822, USA; [email protected] 2 W. M. Keck Laboratory in Astrochemistry, University of Hawaii at Manoa, Honolulu, HI 96822, USA 3 Department of Chemistry, Massachusetts Institute of Technology, Cambridge, MA 02139, USA Received 2021 April 9; revised 2021 May 19; accepted 2021 May 20; published 2021 July 29 Abstract The formation of complex organic molecules by energetic electrons mimicking secondary electrons generated within trajectories of galactic cosmic rays was investigated in interstellar ice analog samples of carbon monoxide and water at 5 K. Simulating the transition from cold molecular clouds to star-forming regions, newly formed products sublimed during the temperature-programmed desorption and were detected utilizing isomer-specific photoionization reflectron time-of-flight mass spectrometry. Using isotopically labeled ices, tunable photoionization, and adiabatic ionization energies to discriminate between isomers, isomers up to C24HO2 and C262HO were identified, while non-isomer- specific findings confirmed complex organics with molecular formulas up to C464HO. The results provide important constraints on reaction pathways from simple inorganic precursors to complex organic molecules that have both astrochemical and astrobiological significance.
    [Show full text]
  • Plant Productivity and the Control of Photorespiration
    Proc. Nat. Acad. Sci. USA Vol. 70, No. 2, pp. 579-584, February 1973 N.A.S. SYMPOSIUM: PLANT GROWTH REGULATION Chairman: R. H. Burris Plant Productivity and the Control of Photorespiration ISRAEL ZELITCH Department of Biochemistry, Connecticut Agricultural Experiment Station, New Haven, Conn. 06504 The Green Revolution of the last decade has seen the yield stalk), and hay grasses (3). The higher-yielding leafy species of some food crops at least doubled by genetic alterations of all have low fluxes of photorespiration compared with the less plant stature and the ability of plants to respond to increased efficient species. fertilizer. Since only 5-10% of the dry weight of plants comes Table 2 contains typical values of CO2 assimilation taken from minerals and nitrogen in the soil, it is becoming more from the literature; it shows that much faster rates are difficult to obtain further increases in productivity by this usually found in the higher-yielding tropical grasses and in approach. Even scientists associated with the Green Revolu- some weeds, as compared with many common crop plants- tion believe they have reached a plateau by these methods (1). including spinach, tobacco, and orchard grass-that are Therefore, the next large increases in productivity must come lower yielding. A large part of the differences in net photo- from increasing the 90-95% of the dry weight that comes synthesis between the efficient and nonefficient species can from the assimilation of airborne CO2 during photosynthesis. be explained by the much slower rate of photorespiration The productivity of plants (dry weight per unit of ground that is encountered naturally only in the efficient plants.
    [Show full text]