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Plant biochemistry / by Hans-Walter Held, Birgit Piechulla. — 4th ed. — Amsterdam : Elsevier, c2011. – (58.842/H474/4th ed.) |
Contents
Contents
Preface xxi
Introduction xxiii
1 A leaf cell consists of several metabolic compartments 1
1.1 The cell wall gives the plant cell mechanical stability 4
The cell wall consists mainly of carbohydrates and proteins 4
Plasmodesmata connect neighboring cells 7
1.2 Vacuoles have multiple functions 9
1.3 Plastids have evolved from cyanobacteria 11
1.4 Mitochondria also result from endosymbionts 15
1.5 Peroxisomes are the site of reactions in which toxic intermediates are formed
1.6 The endoplasmic reticulum and Golgi apparatus form a network for the distribution of biosynthesis products 18
1.7 Functionally intact cell organelles can be isolated from plant cells 22
1.8 Various transport processes facilitate the exchange of metabolites between different compartments 24
1.9 Translocators catalyze the specific transport of metabolic substrates and products Metabolite transport is achieved by a conformational change of the translocator Aquaporins make cell membranes permeable for water 31
1.10 Ion channels have a very high transport capacity 32
1.11 Porins consist of β-sheet structures 37
Further reading 40
2 The use of energy from sunlight by photosynthesis is the basis of life on earth
2.1 How did photosynthesis start? 43
2.2 Pigments capture energy from sunlight 45
The energy content of light depends on its wavelength 45
Chlorophyll is the main photosynthetic pigment 47
2.3 Light absorption excites the chlorophyll molecule 50
2.4 An antenna is required to capture light 54
How is the excitation energy of the photons captured in the antennae and transferred to the reaction centers? 56
The function of an antenna is illustrated by the antenna of photosystem II 57
Phycobilisomes enable cyanobacteria and red algae to carry out photosynthesis even in dim light 60
Further reading 64
3 Photosynthesis is an electron transport process 65
3.1 The photosynthetic machinery is constructed from modules 65
3.2 A reductant and an oxidant are formed during photosynthesis 69
3.3 The basic structure of a photosynthetic reaction center has been resolved by X-ray structure analysis 70
3.4 X-ray structure analysis of the photosynthetic reaction center 72
3.5 The reaction center of Rhodopseudomonas viridis has a symmetrical structure
3.6 How does a reaction center function? 75
3.7 Two photosynthetic reaction centers are arranged in tandem in photosynthesis of algae and plants 79
Water is split by photosystem II 82
Photosystem II complex is very similar to the reaction center in purple bacteria
Mechanized agriculture usually necessitates the use of herbicides 88
The cytochrome-b6/fcomplex mediates electron transport between photosystem II and photosystem I 90
Iron atoms in cytochromes and in iron-sulfur centers have a central function as redox carriers 90
The electron transport by the cytochrome-b6/fcomplex is coupled to a proton transport 93
The number of protons pumped through the cyt-b6/fcomplex can be doubled by a Q-cycle
3.8 Photosystem I reduces NADP+ 98
The light energy driving the cyclic electron transport of PSI is only utilized for the synthesis of ATP 101
3.9 In the absence of other acceptors electrons can be transferred from photosystem I to oxygen 102
3.10 Regulatory processes control the distribution of the captured photons between the two photosystems 106
Excess light energy is eliminated as heat 108
Further reading 110
4 ATP is generated by photosynthesis 113
4.1 A proton gradient serves as an energy-rich intermediate state during ATP synthesis 114
4.2 The electron chemical proton gradient can be dissipated by uncouplers to heat
The chemiosmotic hypothesis was proved experimentally 119
4.3 H+-ATP synthases from bacteria， chloroplasts， and mitochondria have a common basic structure 119
X-ray structure analysis of the F1 part of ATP synthase yields an insight into the machinery of ATP synthesis 123
4.4 The synthesis of ATP is effected by a conformation change of the protein 125
In photosynthetic electron transport the stoichiometry between the formation of NADPH and ATP is still a matter of debate 128
H+-ATP synthase of chloroplasts is regulated by light 129
V-ATPase is related to the F-ATP synthase 129
Further reading 130
5 Mitochondria are the power station of the cell 133
5.1 Biological oxidation is preceded by a degradation of substrates to form bound hydrogen and CO2 133
5.2 Mitochondria are the sites of cell respiration 134
Mitochondria form a separated metabolic compartment 135
5.3 Degradation of substrates applicable for biological oxidation takes place in the matrix compartment 136
Pyruvate is oxidized by a multienzyme complex 136
Acetate is completely oxidized in the citrate cycle 140
A loss of intermediates of the citrate cycle is replenished by anaplerotic
reactions 142
5.4 How much energy can be gained by the oxidation of NADH? 144
5.5 The mitochondrial respiratory chain shares common features with the photosynthetic electron transport chain 145
The complexes of the mitochondrial respiratory chain 147
5.6 Electron transport of the respiratory chain is coupled to the synthesis of ATP via proton transport 151
Mitochondrial proton transport results in the formation of a membrane potential 153
5.7 Mitochondrial ATP synthesis serves the energy demand of the cytosol 154
Plant mitochondria have special metabolic functions 155
Mitochondria can oxidize surplus NADH without forming ATP 156
NADH and NADPH from the cytosol can be oxidized by the respiratory chain of plant mitochondria 158
5.8 Compartmentation of mitochondrial metabolism requires specific membrane translocators 159
Further reading 160
6 The Calvin cycle catalyzes photosynthetic CO2 assimilation 163
6.1 CO2 assimilation proceeds via the dark reaction of photosynthesis 163
6.2 Ribulose bisphosphate carboxylase catalyses the fixation of CO2 166
The oxygenation of ribulose bisphosphate: a costly side-reaction 168
Ribulose bisphosphate carboxylase/oxygenase: special features 170
Activation of ribulose bisphosphate carboxylase/oxygenase 170
6.3 The reduction of 3-phosphoglycerate yields triose phosphate 172
6.4 Ribulose bisphosphate is regenerated from triose phosphate 174
6.5 Beside the reductive pentose phosphate pathway there is also an oxidative pentose phosphate pathway 181
6.6 Reductive and oxidative pentose phosphate pathways are regulated 185
Reduced thioredoxins transmit the signal "illumination" to the enzymes 185
The thioredoxin modulated activation of chloroplast enzymes releases a built-in blockage 187
Multiple regulatory processes tune the reactions of the reductive pentose phosphate pathway 188
Further reading 190
7 Phosphoglycolate formed by the oxygenase activity of RubisCO is recycled in the photorespiratory pathway 193
7.1 Ribulose 1，5-bisphosphate is recovered by recycling 2-phosphoglycolate 193
7.2 The NH4+ released in the photorespiratory pathway is refixed in the chloroplasts 199
7.3 Peroxisomes have to be provided with external reducing equivalents for the reduction of hydroxypyruvate 201
Mitochondria export reducing equivalents via a malate-oxaloacetate shuttle 203
A "malate valve" controls the export of reducing equivalents from the chloroplasts
7.4 The peroxisomal matrix is a special compartment for the disposal of toxic products 205
7.5 How high are the costs of the ribulose bisphosphate oxygenase reaction for the plant? 206
7.6 There is no net CO2 fixation at the compensation point 207
7.7 The photorespiratory pathway， although energy-consuming， may also have a useful function for the plant 208
Further reading 209
8 Photosynthesis implies the consumption of water 211
8.1 The uptake of CO2 into the leaf is accompanied by an escape of water vapor 211
8.2 Stomata regulate the gas exchange of a leaf 213
Malate plays an important role in guard cell metabolism 213
Complex regulation governs stomatal opening 215
8.3 The diffusive flux of CO2 into a plant cell 217
8.4 C4 plants perform CO2 assimilation with less water consumption than C3 plants
The CO2 pump in C4 plants 221
C4 metabolism of the NADP-malic enzyme type plants 223
C4 metabolism of the NAD-malic enzyme type 227
C4 metabolism of the phosphoenolpyruvate carboxykinase type 229
Kranz-anatomy with its mesophyll and bundle sheath cells is not an obligatory requirement for C4 metabolism 231
Enzymes of C4 metabolism are regulated by light 231
Products of C4 metabolism can be identified by mass spectrometry 232
C4 plants include important crop plants but also many persistent weeds 232
8.5 Crassulacean acid metabolism allows plants to survive even during a very severe water shortage 233
CO2 fixed during the night is stored as malic acid 234
Photosynthesis proceeds with closed stomata 236
C4 as well as CAM metabolism developed several times during evolution 238
Further reading 238
9 Polysaccharides are storage and transport forms of carbohydrates produced by photosynthesis 241
Starch and sucrose are the main products of C02 assimilation in many plants 242
9.1 Large quantities of carbohydrate can be stored as starch in the cell 242
Starch is synthesized via ADP-glucose 246
Degradation of starch proceeds in two different ways 248
Surplus of photosynthesis products can be stored temporarily in chloroplasts as starch 251
9.2 Sucrose synthesis takes place in the cytosol 253
9.3 The utilization of the photosynthesis product triose phosphate is strictly regulated
Fructose 1，6-bisphosphatase is an entrance valve of the sucrose synthesis pathway
Sucrose phosphate synthase is regulated by metabolites and by covalent modification
Partitioning of assimilates between sucrose and starch is due to the interplay of several regulatory mechanisms 260
Trehalose is an important signal mediator 260
9.4 In some plants assimilates from the leaves are exported as sugar alcohols or oligosaccharides of the raffinose family 261
9.5 Fructans are deposited as storage compounds in the vacuole 264
9.6 Cellulose is synthesized by enzymes located in the plasma membrane 268
Synthesis of callose is often induced by wounding 269
Cell wall polysaccharides are also synthesized in the Golgi apparatus 270
Further reading 270
10 Nitrate assimilation is essential for the synthesis of organic matter 273
10.1 The reduction of nitrate to NH3 proceeds in two reactions 274
Nitrate is reduced to nitrite in the cytosol 276
The reduction of nitrite to ammonia proceeds in the plastids 277
The fixation of NH4+ proceeds in the same way as in the photorespiratory cycle
10.2 Nitrate assimilation also takes place in the roots 280
The oxidative pentose phosphate pathway in leucoplasts provides reducing equivalents for nitrite reduction 280
10.3 Nitrate assimilation is strictly controlled 282
The synthesis of the nitrate reductase protein is regulated at the level of gene expression 283
Nitrate reductase is also regulated by reversible covalent modification 283
14-3-3 proteins are important metabolic regulators 284
There are great similarities between the regulation of nitrate reductase and sucrose phosphate synthase 285
10.4 The end product of nitrate assimilation is a whole spectrum of amino acids
CO2 assimilation provides the carbon skeletons to synthesize the end products of nitrate assimilation 286
The synthesis of glutamate requires the participation of mitochondrial metabolism
Biosynthesis of proline and arginine 289
Aspartate is the precursor of five amino acids 291
Acetolactate synthase participates in the synthesis of hydrophobic amino acids
Aromatic amino acids are synthesized via the shikimate pathway 297
Glyphosate acts as a herbicide 297
A large proportion of the total plant matter can be formed by the shikimate pathway
10.5 Glutamate is precursor for chlorophylls and cytochromes 300
Protophorphyrin is also precursor for heme synthesis 302
Further reading 304
11 Nitrogen fixation enables plants to use the nitrogen of the air for growth 307
11.1 Legumes form a symbiosis with nodule-forming bacteria 308
The nodule formation relies on a balanced interplay of bacterial and plant gene expression 311
Metabolic products are exchanged between bacteroids and host cells 311
Dinitrogenase reductase delivers electrons for the dinitrogenase reaction 313
N2 as well as H~ are reduced by dinitrogenase 314
11.2 N2 fixation can proceed only at very low oxygen concentrations 316
11.3 The energy costs for utilizing N2 as a nitrogen source are much higher than for the utilization of NO3 318
11.4 Plants improve their nutrition by symbiosis with fungi 318
The arbuscular mycorrhiza is widespread 319
Ectomycorrhiza supply trees with nutrients 320
11.5 Root nodule symbioses may have evolved from a pre-existing pathway for the formation of arbuscular mycorrhiza 320
Further reading 321
12 Sulfate assimilation enables the synthesis of sulfur containing compounds 323
12.1 Sulfate assimilation proceeds primarily by photosynthesis 323
Sulfate assimilation has some parallels to nitrogen assimilation 324
Sulfate is activated prior to reduction 325
Sulfite reductase is similar to nitrite reductase 326
H2S is fixed in the amino acid cysteine 327
12.2 Glutathione serves the cell as an antioxidant and is an agent for the detoxification of pollutants 328
Xenobiotics are detoxified by conjugation 329
Phytochelatins protect the plant against heavy metals 330
12.3 Methionine is synthesized from cysteine 332
S-Adenosylmethionine is a universal methylation reagent 332
12.4 Excessive concentrations of sulfur dioxide in the air are toxic for plants
Further reading 335
13 Phloem transport distributes photoassimilates to the various sites of consumption and storage 337
13.1 There are two modes of phloem loading 339
13.2 Phloem transport proceeds by mass flow 341
13.3 Sink tissues are supplied by phloem unloading 342
Starch is deposited in plastids 343
The glycolysis pathway plays a central role in the utilization of carbohydrates
Further reading 348
14 Products of nitrate assimilation are deposited in plants as storage proteins
14.1 Globulins are the most abundant storage proteins 350
14.2 Prolamins are formed as storage proteins in grasses 351
14.3 2S-Proteins are present in seeds of dicot plants 352
14.4 Special proteins protect seeds from being eaten by animals 352
14.5 Synthesis of the storage proteins occurs at the rough endoplasmic reticulum
14.6 Proteinases mobilize the amino acids deposited in storage proteins
Further reading 356
15 Lipids are membrane constituents and function as carbon stores 359
15.1 Polar lipids are important membrane constituents 360
The fluidity of the membrane is governed by the proportion of unsaturated fatty acids and the content of sterols 361
Membrane lipids contain a variety of hydrophilic head groups 363
Sphingolipids are important constituents of the plasma membrane 364
15.2 Triacylglycerols are storage compounds 366
15.3 The de novo synthesis of fatty acids takes place in the plastids 368
Acetyl CoA is a precursor for the synthesis of fatty acids 368
Acetyl CoA carboxylase is the first enzyme of fatty acid synthesis 371
Further steps of fatty acid synthesis are also catalyzed by a multienzyme complex
The first double bond in a newly synthesized fatty acid is formed by a soluble desaturase 375
Acyl ACP synthesized as a product of fatty acid synthesis in the plastids serves two purposes 378
15.4 Glycerol 3-phosphate is a precursor for the synthesis of glycerolipids 378
The ER membrane is the site of fatty acid elongation and desaturation 381
Some of the plastid membrane lipids are synthesized via the eukaryotic pathway
15.5 Triacylglycerols are synthesized in the membranes of the endoplasmatic reticulum
Plant fat is used for human nutrition and also as a raw material in industry 385
Plant fats are customized by genetic engineering 386
15.6 Storage lipids are mobilized for the production of carbohydrates in the glyoxysomes during seed germination 388
The glyoxylate cycle enables plants to synthesize hexoses from acetyl CoA 390
Reactions with toxic intermediates take place in peroxisomes 392
15.7 Lipoxygenase is involved in the synthesis of oxylipins， which are defense and signal compounds 393
Further reading 398
16 Secondary metabolites fulfill specific ecological functions in plants 399
16.1 Secondary metabolites often protect plants from pathogenic microorganisms and herbivores 399
Microorganisms can be pathogens 400
Plants synthesize phytoalexins in response to microbial infection 400
Plant defense compounds can also be a risk for humans 401
16.2 Alkaloids comprise a variety of heterocyclic secondary metabolites
16.3 Some plants emit prussic acid when wounded by animals 404
16.4 Some wounded plants emit volatile mustard oils 405
16.5 Plants protect themselves by tricking herbivores with false amino acids 406
Further reading 407
17 A large diversity of isoprenoids has multiple functions in plant metabolism
17.1 Higher plants have two different synthesis pathways for isoprenoids 411
Acetyl CoA is a precursor for the synthesis of isoprenoids in the cytosol 411
Pyruvate and D-glycerinaldehyde-3-phosphate are the precursors for the synthesis of isopentyl pyrophosphate in plastids 413
17.2 Prenyl transferases catalyze the association of isoprene units 414
17.3 Some plants emit isoprenes into the air 416
17.4 Many aromatic compounds derive from geranyl pyrophosphate 417
17.5 Farnesyl pyrophosphate is the precursor for the synthesis of sesquiterpenes
Steroids are synthesized from farnesyl pyrophosphate 420
17.6 Geranylgeranyl pyrophosphate is the precursor for defense compounds， phytohormones and carotenoids 422
Oleoresins protect trees from parasites 422
Carotene synthesis delivers pigments to plants and provides an important vitamin for humans 423
17.7 A prenyl chain renders compounds lipid-soluble 424
Proteins can be anchored in a membrane by prenylation 425
Dolichols mediate the glucosylation of proteins 426
17.8 The regulation of isoprenoid synthesis 427
17.9 Isoprenoids are very stable and persistent substances 427
Further reading 428
18 Phenylpropanoids comprise a multitude of plant secondary metabolites and cell wall components 431
18.1 Phenylalanine ammonia lyase catalyses the initial reaction of phenylpropanoid metabolism 433
18.2 Monooxygenases are involved in the synthesis of phenols 434
18.3 Phenylpropanoid compounds polymerize to macromolecules 436
Lignans act as defense substances 437
Lignin is formed by radical polymerization of phenylpropanoid derivatives 438
Suberins form gas- and water-impermeable layers between cells 440
Cutin is a gas- and water-impermeable constituent of the cuticle 442
18.4 The synthesis of flavonoids and stilbenes requires a second aromatic ring derived from acetate residues 442
Some stilbenes are very potent natural fungicides 442
18.5 Flavonoids have multiple functions in plants 444
18.6 Anthocyanins are flower pigments and protect plants against excessive light
18.7 Tannins bind tightly to proteins and therefore have defense functions 447
Further reading 449
19 Multiple signals regulate the growth and development of plant organs and enable their adaptation to environmental conditions 451
19.1 Signal chains known from animal metabolism also function in plants 452
G-proteins act as molecular switches 452
Small G-proteins have diverse regulatory functions 453
Ca2+ is a component signal transduction chains 454
The phosphoinositol pathway controls the opening of Ca2+ channels 455
Calmodulin mediates the signal function of Ca2+ ions 457
Phosphorylated proteins are components of signal transduction chains 458
19.2 Phytohormones contain a variety of very different compounds 460
19.3 Auxin stimulates shoot elongation growth 461
19.4 Gibberellins regulate stem elongation 464
19.5 Cytokinins stimulate cell division 467
19.6 Abscisic acid controls the water balance of the plant 469
19.7 Ethylene makes fruit ripen 470
19.8 Plants also contain steroid and peptide hormones 472
Brassinosteroids control plant development 472
Polypeptides function as phytohormones 474
Systemin induces defense against herbivore attack 474
Phytosulfokines regulate cell proliferation 475
A small protein causes the alkalization of cell culture medium 475
Small cysteine-rich proteins regulate self-incompatibility 476
19.9 Defense reactions are triggered by the interplay of several signals
Salicylic acid and jasmonic acid are signal molecules in pathogen defense
19.10 Light sensors regulate growth and development of plants 479
Phytochromes function as sensors for red light 479
Phototropin and cryptochromes are blue light receptors 482
Further reading 483
20 A plant cell has three different genomes 487
20.1 In the nucleus the genetic information is divided among several chromosomes
The DNA sequences of plant nuclear genomes have been analyzed 491
20.2 The DNA of the nuclear genome is transcribed by three specialized RNA polymerases 491
The transcription of structural genes is regulated 492
Promoter and regulatory sequences regulate the transcription of genes 493
Transcription factors regulate the transcription of a gene 494
Small (sm)RNAs inhibit gene expression by inactivating messenger RNAs 494
The transcription of structural genes requires a complex transcription apparatus
The formation of the messenger RNA requires processing 497
rRNA and tRNA are synthesized by RNA polymerase I and III 501
20.3 DNA polymorphism yields genetic markers for plant breeding 501
Individuals of the same species can be differentiated by restriction fragment length polymorphism 502
The RAPD technique is a simple method for investigating DNA polymorphism 505
The polymorphism of micro-satellite DNA is used as a genetic marker 507
20.4 Transposable DNA elements roam through the genome 508
20.5 Viruses are present in most plant cells 509
Retrotransposons are degenerated retroviruses 512
20.6 Plastids possess a circular genome 513
The transcription apparatus of the plastids resembles that of bacteria 516
20.7 The mitochondrial genome of plants varies largely in its size 517
Mitochondrial RNA is corrected after transcription via editing 520
Male sterility of plants caused by the mitochondria is an important tool in hybrid breeding 521
Further reading 525
21 Protein biosynthesis occurs in three different locations of a cell 527
21.1 Protein synthesis is catalyzed by ribosomes 528
A peptide chain is synthesized 529
Specific inhibitors of the translation can be used to decide whether a protein is encoded in the nucleus or the genome of plastids or mitochondria 533
The translation is regulated 533
21.2 Proteins attain their three-dimensional structure by controlled folding 534
The folding of a protein is a multistep process 535
Proteins are protected during the folding process 536
Heat shock proteins protect against heat damage 537
Chaperones bind to unfolded proteins 537
21.3 Nuclear encoded proteins are distributed throughout various cell compartments
Most of the proteins imported into the mitochondria have to cross two membranes
The import of proteins into chloroplasts requires several translocation complexes
Proteins are imported into peroxisomes in the folded state 546
21.4 Proteins are degraded by proteasomes in a strictly controlled manner 547
Further reading 549
22 Biotechnology alters plants to meet requirements of agriculture， nutrition and industry 551
22.1 A gene is isolated 552
A gene library is required for the isolation of a gene 552
A gene library can be kept in phages 554
A gene library can also be propagated in plasmids 555
A gene library is screened for a certain gene 557
A clone is identified by antibodies which specifically detect the gene product
A clone can also be identified by DNA probes 559
Genes encoding unknown proteins can be functionally assigned by complementation
Genes can be identified with the help of transposons or T-DNA 562
22.2 Agrobacteria can transform plant cells 562
The Ti-plasmid contains the genetic information for tumor formation 564
22.3 Ti-plasmids are used as transformation vectors 566
A new plant is regenerated after the transformation of a leaf cell 569
Plants can be transformed by a modified shotgun 571
Protoplasts can be transformed by the uptake of DNA 571
Plastid transformation to generate transgenic plants is advantageous for the environment 573
22.4 Selected promoters enable the defined expression of a foreign gene 575
Gene products are directed into certain subcellular compartments by targeting sequences 576
22.5 Genes can be turned off via plant transformation 576
22.6 Plant genetic engineering can be used for many different purposes 578
Plants are protected against some insects by the BT protein 579
Plants can be protected against viruses by gene technology 581
The generation of fungus-resistant plants is still at an early stage 582
Non-selective herbicides can be used as a selective herbicide by the generation of herbicide-resistant plants 582
Plant genetic engineering is used for the improvement of the yield and quality of crop products 583
Genetic engineering is used to produce renewable resources for industry 583
Genetic engineering provides a chance for increasing the protection of crop plants against environmental stress 584
The introduction of transgenic cultivars requires a risk analysis 585
Further reading 585
Index 587
