Plant Biochemistry (eBook)

Front cover 1
Plant biochemistry 4
Copyright page 5
Contents 8
Preface 22
Introduction 24
Chapter 1 A leaf cell consists of several metabolic compartments 26
1.1 The cell wall gives the plant cell mechanical stability 29
1.2 Vacuoles have multiple functions 34
1.3 Plastids have evolved from cyanobacteria 36
1.4 Mitochondria also result from endosymbionts 40
1.5 Peroxisomes are the site of reactions in which toxic intermediates are formed 42
1.6 The endoplasmic reticulum and Golgi apparatus form a network for the distribution of biosynthesis products 43
1.7 Functionally intact cell organelles can be isolated from plant cells 47
1.8 Various transport processes facilitate the exchange of metabolites between different compartments 49
1.9 Translocators catalyze the specific transport of metabolic substrates and products 51
1.10 Ion channels have a very high transport capacity 57
1.11 Porins consist of & #946
Further reading 65
Chapter 2 The use of energy from sunlight by photosynthesis is the basis of life on earth 68
2.1 How did photosynthesis start? 68
2.2 Pigments capture energy from sunlight 70
2.3 Light absorption excites the chlorophyll molecule 75
2.4 An antenna is required to capture light 79
Further reading 89
Chapter 3 Photosynthesis is an electron transport process 90
3.1 The photosynthetic machinery is constructed from modules 90
3.2 A reductant and an oxidant are formed during photosynthesis 94
3.3 The basic structure of a photosynthetic reaction center has been resolved by X-ray structure analysis 95
3.4 How does a reaction center function? 100
3.5 Two photosynthetic reaction centers are arranged in tandem in photosynthesis of algae and plants 104
3.6 Water is split by photosystem II 107
3.7 The cytochrome-b[sub(6)]/f complex mediates electron transport between photosystem II and photosystem I 115
3.8 Photosystem I reduces NADP[sup(+)] 123
3.9 In the absence of other acceptors electrons can be transferred from photosystem I to oxygen 127
3.10 Regulatory processes control the distribution of the captured photons between the two photosystems 131
Further reading 135
Chapter 4 ATP is generated by photosynthesis 138
4.1 A proton gradient serves as an energy-rich intermediate state during ATP synthesis 139
4.2 The electron chemical proton gradient can be dissipated by uncouplers to heat 142
4.3 H[sup(+)]-ATP synthases from bacteria, chloroplasts, and mitochondria have a common basic structure 144
4.4 The synthesis of ATP is effected by a conformation change of the protein 150
Further reading 155
Chapter 5 Mitochondria are the power station of the cell 158
5.1 Biological oxidation is preceded by a degradation of substrates to form bound hydrogen and CO[sub(2)] 158
5.2 Mitochondria are the sites of cell respiration 159
5.3 Degradation of substrates applicable for biological oxidation takes place in the matrix compartment 161
5.4 How much energy can be gained by the oxidation of NADH? 169
5.5 The mitochondrial respiratory chain shares common features with the photosynthetic electron transport chain 170
5.6 Electron transport of the respiratory chain is coupled to the synthesis of ATP via proton transport 176
5.7 Plant mitochondria have special metabolic functions 180
5.8 Compartmentation of mitochondrial metabolism requires specific membrane translocators 184
Further reading 185
Chapter 6 The Calvin cycle catalyzes photosynthetic CO[sub(2)] assimilation 188
6.1 CO[sub(2)] assimilation proceeds via the dark reaction of photosynthesis 188
6.2 Ribulose bisphosphate carboxylase catalyses the fixation of CO[sub(2)] 191
6.3 The reduction of 3-phosphoglycerate yields triose phosphate 197
6.4 Ribulose bisphosphate is regenerated from triose phosphate 199
6.5 Beside the reductive pentose phosphate pathway there is also an oxidative pentose phosphate pathway 206
6.6 Reductive and oxidative pentose phosphate pathways are regulated 210
Further reading 215
Chapter 7 Phosphoglycolate formed by the oxygenase activity of RubisCO is recycled in the photorespiratory pathway 218
7.1 Ribulose 1,5-bisphosphate is recovered by recycling 2-phosphoglycolate 218
7.2 The NH[sub(4)][sup(+)] released in the photorespiratory pathway is refixed in the chloroplasts 224
7.3 Peroxisomes have to be provided with external reducing equivalents for the reduction of hydroxypyruvate 226
7.4 The peroxisomal matrix is a special compartment for the disposal of toxic products 230
7.5 How high are the costs of the ribulose bisphosphate oxygenase reaction for the plant? 231
7.6 There is no net CO[sub(2)] fixation at the compensation point 232
7.7 The photorespiratory pathway, although energy-consuming, may also have a useful function for the plant 233
Further reading 234
Chapter 8 Photosynthesis implies the consumption of water 236
8.1 The uptake of CO[sub(2)] into the leaf is accompanied by an escape of water vapor 236
8.2 Stomata regulate the gas exchange of a leaf 238
8.3 The diffusive flux of CO[sub(2)] into a plant cell 242
8.4 C[sub(4)] plants perform CO[sub(2)] assimilation with less water consumption than C[sub(3)] plants 245
8.5 Crassulacean acid metabolism allows plants to survive even during a very severe water shortage 258
Further reading 263
Chapter 9 Polysaccharides are storage and transport forms of carbohydrates produced by photosynthesis 266
Starch and sucrose are the main products of CO[sub(2)] assimilation in many plants 267
9.1 Large quantities of carbohydrate can be stored as starch in the cell 267
9.2 Sucrose synthesis takes place in the cytosol 278
9.3 The utilization of the photosynthesis product triose phosphate is strictly regulated 280
9.4 In some plants assimilates from the leaves are exported as sugar alcohols or oligosaccharides of the raffinose family 286
9.5 Fructans are deposited as storage compounds in the vacuole 289
9.6 Cellulose is synthesized by enzymes located in the plasma membrane 293
Further reading 295
Chapter 10 Nitrate assimilation is essential for the synthesis of organic matter 298
10.1 The reduction of nitrate to NH[sub(3)] proceeds in two reactions 299
10.2 Nitrate assimilation also takes place in the roots 305
10.3 Nitrate assimilation is strictly controlled 307
10.4 The end product of nitrate assimilation is a whole spectrum of amino acids 311
10.5 Glutamate is precursor for chlorophylls and cytochromes 325
Further reading 329
Chapter 11 Nitrogen fixation enables plants to use the nitrogen of the air for growth 332
11.1 Legumes form a symbiosis with nodule-forming bacteria 333
11.2 N[sub(2)] fixation can proceed only at very low oxygen concentrations 341
11.3 The energy costs for utilizing N[sub(2)] as a nitrogen source are much higher than for the utilization of NO[sup(-)][sub(3)] 343
11.4 Plants improve their nutrition by symbiosis with fungi 343
11.5 Root nodule symbioses may have evolved from a pre-existing pathway for the formation of arbuscular mycorrhiza 345
Further reading 346
Chapter 12 Sulfate assimilation enables the synthesis of sulfur containing compounds 348
12.1 Sulfate assimilation proceeds primarily by photosynthesis 348
12.2 Glutathione serves the cell as an antioxidant and is an agent for the detoxification of pollutants 353
12.3 Methionine is synthesized from cysteine 357
12.4 Excessive concentrations of sulfur dioxide in the air are toxic for plants 359
Further reading 360
Chapter 13 Phloem transport distributes photoassimilates to the various sites of consumption and storage 362
13.1 There are two modes of phloem loading 364
13.2 Phloem transport proceeds by mass flow 366
13.3 Sink tissues are supplied by phloem unloading 367
Further reading 373
Chapter 14 Products of nitrate assimilation are deposited in plants as storage proteins 374
14.1 Globulins are the most abundant storage proteins 375
14.2 Prolamins are formed as storage proteins in grasses 376
14.3 2S-Proteins are present in seeds of dicot plants 377
14.4 Special proteins protect seeds from being eaten by animals 377
14.5 Synthesis of the storage proteins occurs at the rough endoplasmic reticulum 378
14.6 Proteinases mobilize the amino acids deposited in storage proteins 381
Further reading 381
Chapter 15 Lipids are membrane constituents and function as carbon stores 384
15.1 Polar lipids are important membrane constituents 385
15.2 Triacylglycerols are storage compounds 391
15.3 The de novo synthesis of fatty acids takes place in the plastids 393
15.4 Glycerol 3-phosphate is a precursor for the synthesis of glycerolipids 403
15.5 Triacylglycerols are synthesized in the membranes of the endoplasmatic reticulum 409
15.6 Storage lipids are mobilized for the production of carbohydrates in the glyoxysomes during seed germination 413
15.7 Lipoxygenase is involved in the synthesis of oxylipins, which are defense and signal compounds 418
Further reading 423
Chapter 16 Secondary metabolites fulfill specific ecological functions in plants 424
16.1 Secondary metabolites often protect plants from pathogenic microorganisms and herbivores 424
16.2 Alkaloids comprise a variety of heterocyclic secondary metabolites 427
16.3 Some plants emit prussic acid when wounded by animals 429
16.4 Some wounded plants emit volatile mustard oils 430
16.5 Plants protect themselves by tricking herbivores with false amino acids 431
Further reading 432
Chapter 17 A large diversity of isoprenoids has multiple functions in plant metabolism 434
17.1 Higher plants have two different synthesis pathways for isoprenoids 436
17.2 Prenyl transferases catalyze the association of isoprene units 439
17.3 Some plants emit isoprenes into the air 441
17.4 Many aromatic compounds derive from geranyl pyrophosphate 442
17.5 Farnesyl pyrophosphate is the precursor for the synthesis of sesquiterpenes 444
17.6 Geranylgeranyl pyrophosphate is the precursor for defense compounds, phytohormones and carotenoids 447
17.7 A prenyl chain renders compounds lipid-soluble 449
17.8 The regulation of isoprenoid synthesis 452
17.9 Isoprenoids are very stable and persistent substances 452
Further reading 453
Chapter 18 Phenylpropanoids comprise a multitude of plant secondary metabolites and cell wall components 456
18.1 Phenylalanine ammonia lyase catalyses the initial reaction of phenylpropanoid metabolism 458
18.2 Monooxygenases are involved in the synthesis of phenols 459
18.3 Phenylpropanoid compounds polymerize to macromolecules 461
18.4 The synthesis of flavonoids and stilbenes requires a second aromatic ring derived from acetate residues 467
18.5 Flavonoids have multiple functions in plants 469
18.6 Anthocyanins are flower pigments and protect plants against excessive light 471
18.7 Tannins bind tightly to proteins and therefore have defense functions 472
Further reading 474
Chapter 19 Multiple signals regulate the growth and development of plant organs and enable their adaptation to environmental conditions 476
19.1 Signal chains known from animal metabolism also function in plants 477
19.2 Phytohormones contain a variety of very different compounds 485
19.3 Auxin stimulates shoot elongation growth 486
19.4 Gibberellins regulate stem elongation 489
19.5 Cytokinins stimulate cell division 492
19.6 Abscisic acid controls the water balance of the plant 494
19.7 Ethylene makes fruit ripen 495
19.8 Plants also contain steroid and peptide hormones 497
19.9 Defense reactions are triggered by the interplay of several signals 501
19.10 Light sensors regulate growth and development of plants 504
Further reading 508
Chapter 20 A plant cell has three different genomes 512
20.1 In the nucleus the genetic information is divided among several chromosomes 513
20.2 The DNA of the nuclear genome is transcribed by three specialized RNA polymerases 516
20.3 DNA polymorphism yields genetic markers for plant breeding 526
20.4 Transposable DNA elements roam through the genome 533
20.5 Viruses are present in most plant cells 534
20.6 Plastids possess a circular genome 538
20.7 The mitochondrial genome of plants varies largely in its size 542
Further reading 550
Chapter 21 Protein biosynthesis occurs in three different locations of a cell 552
21.1 Protein synthesis is catalyzed by ribosomes 553
21.2 Proteins attain their three-dimensional structure by controlled folding 559
21.3 Nuclear encoded proteins are distributed throughout various cell compartments 565
21.4 Proteins are degraded by proteasomes in a strictly controlled manner 572
Further reading 574
Chapter 22 Biotechnology alters plants to meet requirements of agriculture, nutrition and industry 576
22.1 A gene is isolated 577
22.2 Agrobacteria can transform plant cells 587
22.3 Ti-plasmids are used as transformation vectors 591
22.4 Selected promoters enable the defined expression of a foreign gene 600
22.5 Genes can be turned off via plant transformation 601
22.6 Plant genetic engineering can be used for many different purposes 603
Further reading 610
Index 612
A 612
B 615
C 616
D 620
E 621
F 622
G 624
H 626
I 627
J 628
K 628
L 628
M 629
N 632
O 633
P 634
Q 639
R 639
S 641
T 644
U 646
V 646
W 647
X 647
Y 647
Z 647