PHOTORESPIRATION(C2 cycle)/Glycolate Cycle/PCO Cycle

This power point presentation consisting of 41 slides is an attempt to describe what is photorespiration,major photorespiratory pathway in C3 plants ,why photorespiration doesnot take place in C4 plants,structure of Rubisco enzyme ,difference between Photorespiration and Dark respiration and Significance of Photorespiration

1. Photorespiration(C2-Cycle) / Glycolate Cycle / photosynthetic carbon oxidation cycle (PCO-Cycle ) Significant Contributors Gleb Krotkov (1963) Nathan Edward (Ed) Tolbert (1919–1998) By Prof Ichha Purak Department of Botany Ranchi Women’s College,Ranchi

2. 6/21/2021 Photorespiration 2 CONTENTS HISTORY AND INTRODUCTION Major photorespiratory pathway in C3 plants : Reactions Photorespiration does not occur in C4 plants In C4 plants, chloroplasts are dimorphic in nature. STRUCTURE OF RUBISCO ENZYME Differences between Photorespiration and DARK Respiration SIGNIFICANCE OF PHOTORESPIRATION REFERENCES BOOKS CONSULTED

3. Photorespiration is defined as the process of respiration (uptake of oxygen and release of carbon dioxide ) in the presence of light in photosynthesizing tissue . Photorespiration was first described by Decker (1959) who mentioned that rate of respiration in chlorophyllous cells is much higher in light than in dark . Krotkov (1963) introduced the term photorespiration for enhanced respiration ( CO2 evolution) in photosynthetic tissue of leaves of C3 plants in light than in darkness, in the book Plant Physiology by Bidwell (1983 ). Photorespiration differs from normal or Dark respiration, it is not related with glycolysis and tricarboxylic acid cycle . Photorespiration and Dark respiration are also different in sensitivity towards O2, temperature and metabolic inhibitors . 6/21/2021 Photorespiration 3 HISTORY AND INTRODUCTION

4. The process of photorespiration takes place involving chloroplast, peroxisome and mitochondria. Peroxisomes exist almost exclusively in photosynthetic tissue and often appear in direct contact with chloroplast (Electron micrograph) (Figure:-1A) Figure :-1 Electron micrographs of peroxisomes found in plant cells. (A) A peroxisome with a paracrystalline core in a tobacco leaf mesophyll cell. Its close association with chloroplasts and mitochondria is thought to facilitate the exchange of materials between these organelles during photorespiration (From Molecular Biology of the Cell. 4th edition . Alberts et al 2002) 6/21/2021 Photorespiration 4

5. Two types of respiration occur in leaves of C3 plants ,one is mitochondrial respiration which occurs in all plants both during day and night and other is much rapid enhanced respiration which occurs only during day time that is photorespiration. These two processes are spatially separated within the cell, normal respiration occurs in the cytosol and mitochondria whereas photorespiration takes place with the help of chloroplast, peroxisome and mitochondria in co-operative way. 6/21/2021 Photorespiration 5 Photorespiration occurs when the Calvin cycle enzyme ribulose-1,5-bisphosphate-carboxylase/ oxygenase (RUBISCO,EC-4.1.1.39 ) acts on oxygen rather than carbon dioxide. ( Maurino and Peterhansel,2010 and Peterhansel and Maurino , 2011). Rubisco catalyzes entrance reactions of both photosynthesis and photorespiration.

6. 6/21/2021 Photorespiration 6 In photosynthesis, carbon dioxide fixation results in two molecules of 3 phosphoglycerate (3PGA) a 3 carbon compound ,which ultimately form sugars, w hereas in photorespiration oxygen fixation results in formation of one molecule of 3PGA and one molecule of 2 phosphoglycolate (2 C compound ) Later (2 phosphoglycolate ) is converted back to 3PGA in the photorespiratory cycle . This pathway requires energy (ATP) and reducing power (NADPH) (Figure :-2) ( Peterhansel et al 2010). In photorespiration , Ammonia (NH3) and CO2 are released which are refixed later on. Under moderate environmental conditions, approximately each fourth reaction catalyzed by RUBISCO is an oxygenase reaction . The reactions by which Glycolate is converted to 3PGA via Glyoxylate , Glycine, Serine and other 3 carbon acids are known as Glycolate Pathway, which consumes energy and reducing equivalents and part of the fixed carbon is again released as CO2. ( Orgen 1984 and Tolbert 1981,1997)

7. Figure :-2 Schematic overview of photosynthesis and photorespiration by RUBISCO.From Photorespiration by Peterhansel et al (2010) 6/21/2021 Photorespiration 7 Ribulose-1,5-bisphosphate carboxylase/ oxygenase (RUBISCO) catalyzes both CO2 and O2 fixation. The product of CO2 fixation is phosphoglycerate (P- glycerate ) that enters the Calvin cycle. During oxygenation, equimolar amounts of P- glycerate and phosphoglycolate ( P- glycolate ) are formed. P- glycolate is recycled to P- glycerate in the photorespiratory pathway.

8. In animals and bacteria, only one kind of respiration occurs which is not affected by the presence or absence of light . But in certain green plants and Algae there are two distinct types of respirations ,as dark respiration and photorespiration Respiration that occurs in photosynthetic tissues in the presence of light and consumption of oxygen just like mitochondrial respiration results in increased rate of carbon dioxide evolution is called photorespiration or light respiration. It is also called as C2 cycle because first main product phosphoglycolate and some other metabolites like glyoxylate and glycine are 2-C compounds . It is also known as photosynthetic carbon oxidation cycle (PCO-cycle ). Photorespiration is a special type of respiration shown by some green plants, when exposed to light. The normal dark respiration (usual mitochondrial respiration) as a rule is independent of light, its rate remains same in light as well as in dark. 6/21/2021 Photorespiration 8

9. Photorespiration is closely related to CO2 compensation point, it usually occurs only in those plants which have comparatively high CO2 compensation point such as tomato, wheat, oats, green alga Chlorella etc. ( C3 plants ) . It is insignificant or rather absent in plants which have very low CO2 compensation point such as maize,sugarcane,etc . ( C4 plants) Net CO2 fixation is the amount by which photosynthesis exceeds respiration , because respiration continuously releases CO2. Respiration of C3 leaves during darkness is small compared with photosynthetic ratio (1/8th ),rate of respiration in C3 plants during day is 2-3 times higher than rate of respiration in darkness. 6/21/2021 Photorespiration 9 Photorespiration occurs only in temperate C3 plants such as Rice, wheat, barley, legumes as bean etc during daytime only usually when there is high concentration of oxygen . Like normal respiration this process also releases CO2 but does not produce ATP, thus seems to be a wasteful process.

10. Photorespiration is a catabolic process occurring only in presence of light in chlorophyllous tissue of plants in which O2 is consumed and CO2 is released . Specially C3 plants, face the problem of photorespiration. In hot, dry, sunny days these plants tend to close their stomata to prevent excessive loss of water (by transpiration ). In this condition carbon dioxide cannot enter the leaves (via the stomata) ,as a result levels of carbon dioxide within the leaves become low and oxygen (O2) concentration in the leaf becomes higher than carbon dioxide (CO2) concentration. Since there are few carbon dioxide molecules to fix, the oxygen molecules are used as a substitute to produce 3PGA Photorespiration is stimulated by i) high O2 levels ii) low CO2 levels and iii) high temperature 6/21/2021 Photorespiration 10

11. . Figure:-3 Role of peroxisomes in photorespiration From :- Peroxisomes The Cell: A Molecular Approach. 2nd edition.Cooper GM.Sunderland (MA): Sinauer Associates; 2000 Phosphoglycolate is converted to glycolate , which is then transferred to peroxisomes, where it is oxidized and converted to glycine. Glycine is then transferred to mitochondria and converted to serine. The serine is returned to peroxisomes and converted to glycerate , which is transferred back to chloroplasts and enter again in Calvin Cycle (Figure:-3) 6/21/2021 Photorespiration 11 During dark reaction of photosynthesis ,CO2 is added to 5C compound Ribulose 1,5,biphosphate by the enzyme Rubisco resulting in formation of 2 molecules 3PGA (a 3C compound ) which is later on forms carbohydrates . However this enzyme sometimes catalyzes addition of O2 to Ribulose 1,5 bi phosphate resulting in formation of 2C compound phosphoglycolate

12. 6/21/2021 Photorespiration 12 Figure :- 4 Flow chart diagram showing involvement of Chloroplast, Peroxisome and Mitochondria in Photorespiration (Light Respiration )

13. 6/21/2021 Photorespiration 13 Figure:-5 The reactions of Glycolate Cycle (Photorespiration) /C2 cycle

14. 6/21/2021 Photorespiration 14 Major photorespiratory pathway in C3 plants : Reactions Glycolate (Glycolic acid ) is chief metabolite and also substrate of photorespiration Other important metabolites are glycine and serine . In Photorespiration glycolate is oxidized with release of CO2 (Post illumination burst Various steps of the glycolate metabolism or photorespiration (synthesis of glycolate and its oxidation with subsequent release of CO2 ) are as follows :-

15. 6/21/2021 Photorespiration 15 When carbon dioxide concentration in the atmosphere becomes less and oxygen concentration inside photosynthetic tissue increases , O2 competes with CO2 so ribulose 1-5 b iphosphate combines with oxygen to form one molecule each of 3 phosphoglyceric acid (3PGA) and 2 phosphoglycolic acid (2 carbon compound) in the presence of enzyme RuBP carboxylase oxygenase .( Rubisco ). Glycolate is derived from carbons 1 and 2 of RUBP in presence of oxygen . Ribulose 1-5 diphosphate + O2 → 3PGA +2 phosphoglycolic acid

16. 6/21/2021 Photorespiration 16 ii) 3PGA is used up in the Calvin cycle, whereas phosphoglycolic acid is dephosphorylated to form glycolic acid in the chloroplasts by the enzyme phosphatase Phosphoglycolic acid+H2O → Glycolic acid + H3PO4 Further metabolism of Glycolic acid involves two other intracellular organelles peroxisome and mitochondria.

17. 6/21/2021 Photorespiration 17 iii) The glycolic acid synthesized in chloroplast is then transported to peroxisome, where it reacts with oxygen (oxidized) to form glyoxylic acid and H2O2 (Hydrogen peroxide) in the presence of enzyme glycolic acid oxidase. Glycolic acid (Glycolate) +O2 → Glyoxylic acid + H2O2 H2O2 converts into water and oxygen in the presence of enzyme, catalase. 2 H2O2 → 2 H2O+O2

18. 6/21/2021 Photorespiration 18 iv) Glyoxylate is now converted into an amino acid glycine . This is a transamination reaction ,which takes place at the expense of L- Glutamate and in the presence of the enzyme L Glutamate Glyoxylate transaminase Glyoxylate + L-Glutamate   Ketoglutaric acid + Glycine

19. 6/21/2021 Photorespiration 19 v) The glycine formed in peroxisome migrates into mitochondrion where 2 molecules of glycine react to form one molecule of another amino acid Serine with liberation of CO2 (post illumination burst of CO2) & and also NH3. This reaction is catalyzed by the enzyme Serine hydroxymethyltransferase This mitochondrial reaction is major source of CO2 that is released in photorespiration. In the first step one molecule of Glycine is cleaved by the enzyme Glycine synthase into 3 parts - carboxylic group, amino group and methylene carbon. COOH and NH2 group are eliminated as CO2 and NH3. Methylene carbon becomes bound to Tetrahydrofolate as Methylene THF. The reaction requires NAD+, as a result NADH is produced which is later on oxidized by Electron Transport Chain (ETC) in mitochondria .

20. 6/21/2021 Photorespiration 20 In the second step Serine is formed by transfer of methylene carbon from THF to second Glycine molecule by Serine hydroxyl methyltransferase ( Pyridoxal phosphate requiring enzyme ). NH3 liberated in this stage is again utilized to synthesize L Glutamate by Glutamate dehydrogenase present in mitochondria . Glycine + THF+NAD +  CO2 + CH2-THF+NH3+NADH Glycine + CH2-THF  Serine + THF ----------------------------------------------------------------------------- 2 Glycine+ NAD+  Serine +CO2 + NH3+ NADH

21. 6/21/2021 Photorespiration 21 vi) The Serine passes back to the peroxisome where it is deaminated to hydroxpyruvate in presence of Serine : Glyoxylate amino transferase Serine + glyoxylate  Hydroxypyruvate + glycine

22. 6/21/2021 Photorespiration 22 vii) Hydroxyruvate is now reduced in peroxisome by the NAD requiring hydroxypyruvate reductase to form glyceric acid . Hydroxypyruvate + NADH  Glyceric acid + NAD+

23. 6/21/2021 Photorespiration 23 Glyceric acid + ATP  3 phosphoglyceric acid + ADP viii ) The glyceric acid ( glycerate ) now diffuse into the chloroplast where it is phosphorylated by ATP to 3 Phosphoglyceric acid (3PGA) in the presence of the enzyme glycerate kinase. PGA is intermediate of Calvin cycle.

24. 6/21/2021 Photorespiration 24

25. 6/21/2021 Photorespiration 25 Thus during photorespiration starting from intermediates of Calvin cycle with the synthesis of glycolate , serine is formed which again is converted into Calvin cycle intermediates The conversion of RUBP upto Glycine is irreversible while from glycine to 3PGA is reversible . During photorespiratory pathway, one CO2 molecule is released in mitochondria which is lost in C3 plants whereas is refixed in C4 Plants It has been estimated that as result of photorespiration C3 plants lose 20-40% carbon dioxide fixed by photosynthesis . Such loses in C4 plants are very small so C4 plants grow more efficiently than C3 plants ( Maize,Millet , Sorghum and Sugar cane ) The affinity of Rubisco for CO2 is much higher than for O2, but O2 fixation in all plants can occur because O2 concentration in leaves or cells of algae is much higher than that of CO2 during day time.( by light reaction of photosynthesis O2 is produced)

26. 6/21/2021 Photorespiration 26 At any given time Rubisco enzyme fixes about 1/3 to 1/4 as much O2 as CO2. When temperature is higher the ratio of dissolved chloroplastidic O2 ,compared to CO2 is higher , than when temperature is low So O2 fixation by Rubisco occurs faster and photorespiration then indirectly slows growth. Photorespiration is light dependent , because RUBP formation occurs much faster in light than in darkness. This is so because operation of the Calvin cycle is needed to form RUBP requires ATP + NADPH both light dependent products and light also causes release of O2 from H2O directly in chloroplast and so chloroplastidic O2 is more abundant in light than in darkness .

27. 6/21/2021 Photorespiration 27 Photorespiration does not occur in C4 plants Photorespiration is absent in C4 plants, this is because Rubisco and other Calvin cycle enzymes are present only in Bundle Sheath cells and CO2 concentration in those cells is maintained too high for O2 to compete with CO2 . In bundle sheath cells CO2 concentration are kept high by rapid decarboxylation of malate and aspartate transferred there from mesophyll cells. (Dennis,1987) In C4 plants, initial fixation of CO2 occurs in mesophyll cells . The primary acceptor of carbon dioxide is phosphoenolpyruvate . (Hatch and Slack,1970) It combines with CO2 in the presence of phosphoenol pyruvate carboxylase to form oxaloacetic acid. Oxaloacetic acid is reduced to malic acid. Inside the bundle sheath cells malic acid is decarboxylated to form pyruvate and CO2. Carbon dioxide is again fixed inside the bundle sheath cells through Calvin cycle. RuBP /RUDP is called secondary or final acceptor of CO2 of C4 plants. Therefore, C4 plants have 2 carboxylation reaction.(Figure :-6)

28. 6/21/2021 Photorespiration 28 Figure :- 6 Hatch and Slack Pathway in C4 Plants

29. 6/21/2021 Photorespiration 29 In C4 plants, chloroplasts are dimorphic in nature . Leaves of C4 plants are characterized by presence of tightly packed thick walled bundle sheath cells all around the vascular bundle, the chloroplast present in these cells are large in size ,centripetally arranged and lack well-organized grana . The chloroplast of mesophyll cells are normal having both grana and stroma . Because of the wreath-like configuration of these bundle sheath cells, this arrangement is known as Kranz anatomy . Bundle sheath cells are well protected from oxygen being released from mesophyll cells.(Figure :-7)

30. 6/21/2021 Photorespiration 30 Figure :- 7 T.S . of leaf (C4 plant) showing Kranz Anatomy

31. 6/21/2021 Photorespiration 31 STRUCTURE OF RUBISCO ENZYME Ribulose-1,5-bisphosphate carboxylase/ oxygenase ( Rubisco ) is the enzyme which catalyses the first step of carbon fixation in Calvin cycle . Rubisco also acts as Oxygenase in photorespiration (Figure:- 8 and 9 ) Figure :- 8 Rubisco is two-faced enzyme.

32. 6/21/2021 Photorespiration 32 RubisCO consists of a set of eight large subunits (called L) of 51 to 58 kDa each, and eight small subunits (called S) of 12 to 18 kDa each . The large subunits are encoded in the chloroplast stroma by the chloroplastidic genome. The small subunits are encoded by the nuclear genome of the photosynthetic cells. The folding of the polypeptides corresponding to the subunits and their assembly to form the functional RubisCO involves chaperone proteins . At the functional level, the large sub-units carry the catalytic sites. The small sub-units, have a regulatory role The carboxylase activity of RUBISCO enzyme is low and is competitively inhibited by O2 ,similarly the oxygenase activity is inhibited by CO2. Thus relative ratio of two reactions depend on concentrations of CO2 and O2 in chloroplast stroma .

33. 6/21/2021 Photorespiration 33 Figure :-9 Structure of Rubisco The holoenzyme is composed of eight large subunits (dark blue, light blue) and eight small subunits (red, orange). Active sites that form between two neighboring large subunits are denoted by loop (yellow).

34. 6/21/2021 Photorespiration 34 S N Photorespiration Normal Dark Respiration 1   It takes place only in the presence of light It takes place both in dark and in light. 2   It occurs only in green photosynthetic tissue of C3 plants and very little in C4 plants It occurs in all living tissues of aerobic organisms 3   It is accomplished in cytoplasm , chloroplast,peroxisome and mitochondria It is accomplished in cytoplasm and mitochondria only and involves glycolysis, Krebs cycle and terminal ETC 4   Substrate of photorespirion is Ribulose 1,5, bi phosphate (RUBP) which reacts with oxygen to give 2C phosphoglycolic acid and 3PGA The substrate of mitochondrial respiration is commonly glucose although other food materials (like fat, protein, organic acids) can also be oxidized 5   It consumes O 2 at 3 places and releases CO 2 only at one place O 2 is consumed only in terminal oxidation (through cytochrome oxidase) while CO 2 is released in several places 6   2 molecules of Glycine in mitochondria become converted to serine . In this reaction One molecule of NH 3 is also released along with CO 2 Ammonia is not produced 7   It involves oxidation both by transfer of electrons to O 2 and incorporations of an oxygen atom derived from molecular O 2 . Terminal oxidation involves transfer of electrons to O2 and the formation of water 8   Neither reduced co-enzyme nor ATPs are generated . There is no net conservation of energy. On the contrary , an input of energy is required to drive the C2 cycle Reduced coenzyme and ATPs are formed . Dark respiration involves both substrate level and oxidative phosphorylation . Although ATPs are required in initial steps, but there is net gains of ATPs in the overall process. 9   It is markedly influenced by the Concentration of CO 2 and O 2 . Competetion between CO 2 and O 2 is evident It is not markedly influenced by the concentrations of CO 2 or O 2 . The Competetion between CO 2 and O 2 is not evident. 10   It is not essential. It is a wasteful process, does not produce energy It is essential for survival of organisms, it produces energy Table No.-1 Differences between Photorespiration and Normal Respiration

35. 6/21/2021 Photorespiration 35 SIGNIFICANCE OF PHOTORESPIRATION Disadvantages of Photorespiration in C3 plants. Photorespiration reduces the efficiency of photosynthesis as in this process O2 is used to oxidize RUBP resulting in formation of 3PGA and 2 carbon compound phosphoglycolic acid. During photorespiration unlike usual mitochondrial respiration neither reduced co-enzyme (NADH) is generated nor ATP is formed . Biochemical studies indicate that photorespiration consumes ATP and NADPH, the high-energy molecules made by the light reactions of photosynthesis . Photorespiration is a highly waste full process ,by it about 50% fixed CO2 during photosynthesis is lost in C3 plants and Algae. Photorespiration is considered as a wasteful process as extra energy is consumed for O2 fixation in the form of ATP but on other hand the pathway reuses ¾ of the carbon in phosphoglycolate by regenerating 3PGA .

36. 6/21/2021 Photorespiration 36 Two turns of photorespiratory cycle produce two molecules of Phosphoglycolate by oxygenation which contain 2+2 that is 4 carbon atoms . Of these four C-atoms, one is lost as CO2 in the reaction in which 2 moles of glycine being derived from two molecules of phosphoglycolate change to Serine and NH3 and the remaining 3-C atoms are cycled back to chloroplast as glycerate . Thus glycolate pathway recovers 75% of the carbon which would otherwise be lost as 2-phosphoglycolate from Calvin-cycle. Thus photorespiration can be regarded as an important pathway to overcome situations caused by RUBISCO’s oxygenase activity. C4 plants overcome the problem of photorespiration by performing light reaction in mesophyll cells and Rubisco mediated CO2 fixation by Calvin cycle in the interior of leaves, in the bundle sheath cells where both temperature and oxygen are lower.

37. 6/21/2021 Photorespiration 37 Advantages of Photorespiration Photorespiration plays some positive roles in plant metabolism Photorespiration removes toxic metabolic intermediates This pathway uses toxic phosphoglycolate for regeneration of 3PGA. Phosphoglycolate if not consumed inhibit triose phosphate isomerase that would interfere with the regeneration of Ribulose 1,5 biphosphate in the Calvin cycle. Photorespiration is a major source of H2O2 in plants. H2O2 acts as signal molecule in plants involved in both biotic and abiotic stress responses. H2O2 can damage the pathogen by its reactive potential Many intermediates of Glycolate cycle are part of other metabolic pathways. Photorespiration significantly contributes to synthesis of amino acids as glycine and serine. Serine is used for synthesis of other amino acids as methionine in cytoplasm. Photorespiration connects the metabolic compartments of the cell and facilitate transport among organelles as peroxisome, mitochondria and chloroplast .

38. 6/21/2021 Photorespiration 38 REFERENCES Bidwell, R.G.S. (1983) ‘Carbon nutrition of plants: photosynthesis and respiration’, in Plant Physiology: A Treatise ( F.e . Steward , ed.), Vol. VII, Energy and Carbon Metabolism ( F.e . Steward and R.G.S. Bidwell, eds.), Academic Press, New York, 287–458 . Decker, J.P. (1959) Comparative responses of carbon dioxide outburst and uptake in tobacco.-Plant Physiol. 34: 100–102 Dennis D.T. (1987) Photorespiration. In: The Biochemistry of Energy Utilization in Plants. Springer, Dordrecht: pp 107-113 Dennis D.T. (1987) The Avoidance of Photorespiration: The C4 Plants. In: The Biochemistry of Energy Utilization in Plants. Springer.pp 114-119 Hatch M D and Slack C R (1970) Photosynthetic CO2 –Fixation Pathways Annual Review Plant Physiol.21 : 141-162 Krotkov , G. 1963. Effect of light on respiration. Photosynthetic 'Mechanisms of Green Plants. Nat. Acad. Sci. Puib . 1145: 452-454 . Maurino VG and Peterhansel C (2010) Photorespiration: current status and approaches for metabolic engineering. Curr Opin Plant Biol 13(3): 249–256

39. 6/21/2021 Photorespiration 39 Ogren , W.L. (1984) Photorespiration: pathways, regulation modification. Ann. Rev. Pl. Physiol. 35, 415–442 . Peterhansel,C et al (2010) Photorespiration (In Arabidopsis Book) Peterhansel C and Maurino V G (2011) Photorespiration redesigned .Plant Physiology:155: 49-55 . Tolbert NE. 1980. Photorespiration. In The Biochemistry of Plants, ed. P Stumpf & E Conn, Vol. 2: Metabolism and Respiration, ed. DD Davies, pp. 488–525. New York: Academic Tolbert NE. 1981. Metabolic pathways in peroxisomes and glyoxysomes . Annu . Rev.Biochem . 50:133–157 Tolbert N E (1997 ) The C2 Oxidative photosynthetic carbon cycle. Annu . Rev. Plant Physiol. Plant Mol. Biol. 48:1–25

40. 6/21/2021 Photorespiration 40 BOOKS CONSULTED Molecular Biology of the Cell. 4th edition. Alberts B, Johnson A, Lewis J, et al.New York: Garland Science; 2002 . The Cell: A Molecular Approach. 2nd edition. Cooper GM.Sunderland (MA): Sinauer Associates; 2000. Cell and molecular biology Concepts and Experiments Gerald Karp 5th Edition 2007 John Willey and Sons, Inc Cell Biology ( Cytology,Biomolecules and Molecular Biology) By Verma PS and Agarwal V K ) S Chand & Company Pvt Ltd. Introduction to plant biochemistry by T W Goodwin; E I Mercer ,Oxford, New York, Pergamon Press [1972] Molecular Cell Biology. 4th edition.2000 H Lodish , A Berk and S L Zipursky W. H. Freeman; New York Cell Biology (1997 ) SC Roy and K K De New Central Book Agency (P ) Ltd.Kolkatta , India Opal H, Rolfe S A and Wills A J 2005 The physiology of Flowering Plants (Fourth Edition) Cambridge University Press,New York

41. 6/21/2021 Photorespiration 41