Plant biochemistry / by Hans-Walter Heldt, Birgit Piechulla. -- 4th ed. -- Amsterdam : Elsevier, c2011 .—(58.842/H474/4th ed.)

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

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  17

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  26

1.10  Ion channels have a very high transport capacity  32

1.11  Porins consist of 13-sheet structures  37

Further reading  40

2    The use of energy from sunlight by photosynthesis is the basis of life on earth  43

2.1   How did photosynthesis start?  43

2.2   Pigments capture energy from sunlight  45

2.3   Light absorption excites the chlorophyll molecule  50

2.4   An antenna is required to capture light  54

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   How does a reaction center function?  75

3.5   Two photosynthetic reaction centers are arranged in tandem in photosynthesis of algae and plants  79

3.6   Water is split by photosystem II  82

3.7   The cytochrome-b6/f complex mediates electron transport between photosystem II and photosystem I  90

3.8   Photosystem I reduces NADP+  98

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

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  117

4.3   H+-ATP synthases from bacteria, chloroplasts, and mitochondria have a common basic structure  119

4.4   The synthesis of ATP is effected by a conformation change of the protein  125

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 ceil respiration  134

5.3   Degradation of substrates applicable for biological oxidation takes place in the matrix compartment  136

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

5.6   Electron transport of the respiratory chain is coupled to the synthesis of ATP via proton transport  151

5.7   Plant mitochondria have special metabolic functions  155

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

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

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

7.4   The peroxisomes 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

Further reading  238

9    Polysaccharides are storage and transport forms of carbohydrates produced by photosynthesis  241

9.1   Large quantities of carbohydrate can be stored as starch in the cell  242

9.2   Sucrose synthesis takes place in the cytosol  253

9.3   The utilization of the photosynthesis product triose phosphate is strictly regulated  255

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

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

10.2   Nitrate assimilation also takes place in the roots  280

10.3   Nitrate assimilation is strictly controlled  282

10.4   The end product of nitrate assimilation is a whole spectrum of amino acids  286

10.5   Glutamate is precursor for chlorophylls and cytochromes  300

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

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

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

12.2   Glutathione serves the cell as an antioxidant and is an agent for the detoxification of pollutants  328

12.3   Methionine is synthesized from cysteine  332

12.4   Excessive concentrations of sulfur dioxide in the air are toxic for plants  334

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

Further reading  348

14   Products of nitrate assimilation are deposited in plants as storage proteins  349

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  353

14.6   Proteinases mobilize the amino acids deposited in storage proteins  356

Further reading  356

15   Lipids are membrane constituents and function as carbon stores  359

15.1   Polar lipids are important membrane constituents  360

15.2   Triacylglycerols are storage compounds  366

15.3   The de novo synthesis of fatty acids takes place in the plastids  368

15.4   Glycerol 3-phosphate is a precursor for the synthesis of glycerolipids  378

15.5   Triacylglycerols are synthesized in the membranes of the endoplasmatic reticulum  384

15.6   Storage lipids are mobilized for the production of carbohydrates in the glyoxysomes during seed germination  388

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

16.2   Alkaloids comprise a variety of heterocyclic secondary metabolites  402

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 409

17.1   Higher plants have two different synthesis pathways for isoprenoids  411

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  419

17.6   Geranylgeranyl pyrophosphate is the precursor for defense compounds, phytohormones and carotenoids  422

17.7   A prenyl chain renders compounds lipid-soluble  424

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

18.4   The synthesis of flavonoids and stilbenes requires a second aromatic ring derived from acetate residues  442

18.5   Flavonoids have multiple functions in plants  444

18.6   Anthocyanins are flower pigments and protect plants against excessive light 446

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

19.2   Phytohormones contain a variety of very different compounds  460

19.3   Auxin stimulates shoot elongation growth  461

19.4   Gibberellins regulate stern 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

19.9   Defense reactions are triggered by the interplay of several signals  476

19.10   Light sensors regulate growth and development of plants  479

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  488

20.2   The DNA of the nuclear genome is transcribed by three specialized RNA polymerases  491

20.3   DNA polymorphism yields genetic markers for plant breeding  501

20.4   Transposable DNA elements roam through the genome  508

20.5   Viruses are present in most plant cells  509

20.6   Plastids possess a circular genome  513

20.7   The mitochondrial genome of plants varies largely in its size  517

Further reading  525

21   Protein biosynthesis occurs in three different locations of a cell  527

21.1   Protein synthesis is catalyzed by ribosomes  528

21.2   Proteins attain their three-dimensional structure by controlled folding  534

21.3   Nuclear encoded proteins are distributed throughout various cell compartments  540

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

22.2   Agrobacteria can transform plant cells  562

22.3   Ti-plasmids are used as transformation vectors  566

22.4   Selected promoters enable the defined expression of a foreign gone  575

22.5   Genes can be turned off via plant transformation  576

22.6   Plant genetic engineering can be used for many different purposes  578

Further reading  585

Index  587