Plant Biochemistry

Plant Biochemistry......Page 2
Copyright......Page 3
Dedication......Page 4
Preface......Page 5
Introduction......Page 7
A leaf cell consists of several metabolic compartments......Page 9
The cell wall consists mainly of carbohydrates and proteins......Page 12
Plasmodesmata connect neighboring cells......Page 15
Vacuoles have multiple functions......Page 17
Plastids have evolved from cyanobacteria......Page 19
Mitochondria also result from endosymbionts......Page 23
Peroxisomes are the site of reactions in which toxic intermediates are formed......Page 25
The endoplasmic reticulum and golgi apparatus form a network for the distribution of biosynthesis products......Page 26
Functionally intact cell organelles can be isolated from plant cells......Page 30
Various transport processes facilitate the exchange of metabolites between different compartments......Page 32
Translocators catalyze the specific transport of metabolic substrates and products......Page 34
Metabolite transport is achieved by a conformational change of the translocator......Page 36
Aquaporins make cell membranes permeable for water......Page 39
Ion channels have a very high transport capacity......Page 40
Porins consist of sheet structures......Page 45
How did photosynthesis start?......Page 51
The energy content of light depends on its wavelength......Page 53
Chlorophyll is the main photosynthetic pigment......Page 55
Light absorption excites the chlorophyll molecule......Page 58
An antenna is required to capture light......Page 62
How is the excitation energy of the photons captured in the antennae and transferred to the reaction centers?......Page 64
The function of an antenna is illustrated by the antenna of photosystem II......Page 65
Phycobilisomes enable cyanobacteria and red algae to carry out photosynthesis even in dim light......Page 68
The photosynthetic machinery is constructed from modules......Page 73
A reductant and an oxidant are formed during photosynthesis......Page 77
The basic structure of a photosynthetic reaction center has been resolved by X-ray structure analysis......Page 78
X-ray structure analysis of the photosynthetic reaction center......Page 80
The reaction center of Rhodopseudomonas viridis has a symmetric structure......Page 81
How does a reaction center function?......Page 83
Two photosynthetic reaction centers are arranged in tandem in photosynthesis of algae and plants......Page 87
Water is split by photosystem II......Page 90
Photosystem II complex is very similar to the reaction center in purple bacteria......Page 94
Mechanized agriculture usually necessitates the use of herbicides......Page 96
Iron atoms in cytochromes and in iron-sulfur centers have a central function as redox carriers......Page 98
The electron transport by the cytochrome-b6/f complex is coupled to a proton transport......Page 101
The number of protons pumped through the cyt-b6/f complex can be doubled by a Q-cycle......Page 104
Photosystem I reduces NADP+......Page 106
The light energy driving the cyclic electron transport of PS I is only utilized for the synthesis of ATP......Page 109
In the absence of other acceptors electrons can be transferred from photosystem I to oxygen......Page 110
Regulatory processes control the distribution of the captured photons between the two photosystems......Page 114
Excess light energy is eliminated as heat......Page 116
ATP is generated by photosynthesis......Page 121
A proton gradient serves as an energy-rich intermediate state during ATP synthesis......Page 122
The electron chemical proton gradient can be dissipated by uncouplers to heat......Page 125
H+-ATP synthases from bacteria, chloroplasts, and mitochondria have a common basic structure......Page 127
X-ray structure analysis of the F1 part of ATP synthase yields an insight into the machinery of ATP synthesis......Page 131
The synthesis of ATP is effected by a conformation change of the protein......Page 133
In photosynthetic electron transport the stoichiometry between the formation of NADPH and ATP is still a matter of debate......Page 136
V-ATPase is related to the F-ATP synthase......Page 137
Biological oxidation is preceded by a degradation of substrates to form bound hydrogen and CO2......Page 140
Mitochondria are the sites of cell respiration......Page 141
Mitochondria form a separated metabolic compartment......Page 142
Pyruvate is oxidized by a multienzyme complex......Page 143
Acetate is completely oxidized in the citrate cycle......Page 147
A loss of intermediates of the citrate cycle is replenished by anaplerotic reactions......Page 149
How much energy can be gained by the oxidation of NADH?......Page 151
The mitochondrial respiratory chain shares common features with the photosynthetic electron transport chain......Page 152
The complexes of the mitochondrial respiratory chain......Page 154
Electron transport of the respiratory chain is coupled to the synthesis of ATP via proton transport......Page 158
Mitochondrial proton transport results in the formation of a membrane potential......Page 160
Mitochondrial ATP synthesis serves the energy demand of the cytosol......Page 161
Plant mitochondria have special metabolic functions......Page 162
Mitochondria can oxidize surplus NADH without forming ATP......Page 163
NADH and NADPH from the cytosol can be oxidized by the respiratory chain of plant mitochondria......Page 165
Compartmentation of mitochondrial metabolism requires specific membrane translocators......Page 166
CO2 assimilation proceeds via the dark reaction of photosynthesis......Page 169
Ribulose bisphosphate carboxylase catalyzes the fixation of CO2......Page 172
The oxygenation of ribulose bisphosphate: a costly side-reaction......Page 174
Activation of ribulose bisphosphate carboxylase/oxygenase......Page 176
The reduction of 3-phosphoglycerate yields triose phosphate......Page 178
Ribulose bisphosphate is regenerated from triose phosphate......Page 180
Besides the reductive pentose phosphate pathway there is also an oxidative pentose phosphate pathway......Page 187
Reduced thioredoxins transmit the signal “illumination” to the enzymes......Page 191
The thioredoxin modulated activation of chloroplast enzymes releases a built-in blockage......Page 193
Multiple regulatory processes tune the reactions of the reductive pentose phosphate pathway......Page 194
Ribulose 1,5-bisphosphate is recovered by recycling 2-phosphoglycolate......Page 198
The NH4+ released in the photorespiratory pathway is refixed in the chloroplasts......Page 204
Peroxisomes have to be provided with external reducing equivalents for the reduction of hydroxypyruvate......Page 206
A “malate valve” controls the export of reducing equivalents from the chloroplasts......Page 208
The peroxisomal matrix is a special compartment for the disposal of toxic products......Page 210
How high are the costs of the ribulose bisphosphate oxygenase reaction for the plant?......Page 211
There is no net CO2 fixation at the compensation point......Page 212
The photorespiratory pathway, although energy-consuming, may also have a useful function for the plant......Page 213
The uptake of CO2 into the leaf is accompanied by an escape of water vapor......Page 215
Malate plays an important role in guard cell metabolism......Page 217
Complex regulation governs stomatal opening......Page 219
The diffusive flux of CO2 into a plant cell......Page 221
C4 plants perform CO2 assimilation with less water consumption than C3 plants......Page 224
The CO2 pump in C4 plants......Page 225
C4 metabolism of the NADP-malic enzyme type plants......Page 227
C4 metabolism of the NAD-malic enzyme type......Page 231
C4 metabolism of the phosphoenolpyruvate carboxykinase type......Page 233
Enzymes of C4 metabolism are regulated by light......Page 235
C4 plants include important crop plants but also many persistent weeds......Page 236
Crassulacean acid metabolism allows plants to survive even during a very severe water shortage......Page 237
CO2 fixed during the night is stored as malic acid......Page 238
Photosynthesis proceeds with closed stomata......Page 240
C4 as well as CAM metabolism developed several times during evolution......Page 242
Polysaccharides are storage and transport forms of carbohydrates produced by photosynthesis......Page 244
Large quantities of carbohydrate can be stored as starch in the cell......Page 245
Starch is synthesized via ADP-glucose......Page 249
Degradation of starch proceeds in two different ways......Page 251
Surplus of photosynthesis products can be stored temporarily in chloroplasts as starch......Page 254
Sucrose synthesis takes place in the cytosol......Page 256
Fructose 1,6-bisphosphatase is an entrance valve of the sucrose synthesis pathway......Page 258
Sucrose phosphate synthase is regulated by metabolites and by covalent modification......Page 262
Trehalose is an important signal mediator......Page 263
In some plants assimilates from the leaves are exported as sugar alcohols or oligosaccharides of the raffinose family......Page 264
Fructans are deposited as storage compounds in the vacuole......Page 267
Cellulose is synthesized by enzymes located in the plasma membrane......Page 271
Synthesis of callose is often induced by wounding......Page 272
Cell wall polysaccharides are also synthesized in the Golgi apparatus......Page 273
Nitrate assimilation is essential for the synthesis of organic matter......Page 275
The reduction of nitrate to NH3 proceeds in two reactions......Page 276
Nitrate is reduced to nitrite in the cytosol......Page 278
The reduction of nitrite to ammonia proceeds in the plastids......Page 279
The fixation of NH4+ proceeds in the same way as in the photorespiratory cycle......Page 280
The oxidative pentose phosphate pathway in leucoplasts provides reducing equivalents for nitrite reduction......Page 282
Nitrate assimilation is strictly controlled......Page 284
Nitrate reductase is also regulated by reversible covalent modification......Page 285
14-3-3 proteins are important metabolic regulators......Page 286
There are great similarities between the regulation of nitrate reductase and sucrose phosphate synthase......Page 287
CO2 assimilation provides the carbon skeletons to synthesize the end products of nitrate assimilation......Page 288
The synthesis of glutamate requires the participation of mitochondrial metabolism......Page 290
Biosynthesis of proline and arginine......Page 291
Aspartate is the precursor of five amino acids......Page 293
Acetolactate synthase participates in the synthesis of hydrophobic amino acids......Page 295
Glyphosate acts as a herbicide......Page 299
A large proportion of the total plant matter can be formed by the shikimate pathway......Page 301
Glutamate is the precursor for chlorophylls and cytochromes......Page 302
Protophorphyrin is also precursor for heme synthesis......Page 304
Nitrogen fixation enables plants to use the nitrogen of the air for growth......Page 308
Legumes form a symbiosis with nodule-inducing bacteria......Page 309
Metabolic products are exchanged between bacteroids and host cells......Page 312
Dinitrogenase reductase delivers electrons for the dinitrogenase reaction......Page 314
Plants improve their nutrition by symbiosis with fungi......Page 319
N2 fixation can proceed only at very low oxygen concentrations......Page 317
The arbuscular mycorrhiza is widespread......Page 320
Root nodule symbioses may have evolved from a pre-existing pathway for the formation of arbuscular mycorrhiza......Page 321
Sulfate assimilation proceeds primarily by photosynthesis......Page 324
Sulfate assimilation has some parallels to nitrogen assimilation......Page 325
Sulfate is activated prior to reduction......Page 326
Sulfite reductase is similar to nitrite reductase......Page 327
H2S is fixed in the amino acid cysteine......Page 328
Glutathione serves the cell as an antioxidant and is an agent for the detoxification of pollutants......Page 329
Xenobiotics are detoxified by conjugation......Page 330
Phytochelatins protect the plant against heavy metals......Page 331
S-Adenosylmethionine is a universal methylation reagent......Page 333
Excessive concentrations of sulfur dioxide in the air are toxic for plants......Page 335
Phloem transport distributes photoassimilates to the various sites of consumption and storage......Page 337
There are two modes of phloem loading......Page 339
Phloem transport proceeds by mass flow......Page 341
Sink tissues are supplied by phloem unloading......Page 342
The glycolysis pathway plays a central role in the utilization of carbohydrates......Page 343
Products of nitrate assimilation are deposited in plants as storage proteins......Page 349
Globulins are the most abundant storage proteins......Page 350
Prolamins are formed as storage proteins in grasses......Page 351
Special proteins protect seeds from being eaten by animals......Page 352
Synthesis of the storage proteins occurs at the rough endoplasmic reticulum......Page 353
Proteinases mobilize the amino acids deposited in storage proteins......Page 356
Lipids are membrane constituents and function as carbon stores......Page 358
Polar lipids are important membrane constituents......Page 359
The fluidity of the membrane is governed by the proportion of unsaturated fatty acids and the content of sterols......Page 360
Membrane lipids contain a variety of hydrophilic head groups......Page 362
Sphingolipids are important constituents of the plasma membrane......Page 363
Triacylglycerols are storage compounds......Page 365
Acetyl CoA is a precursor for the synthesis of fatty acids......Page 367
Acetyl CoA carboxylase is the first enzyme of fatty acid synthesis......Page 370
Further steps of fatty acid synthesis are also catalyzed by a multienzyme complex......Page 372
The first double bond in a newly synthesized fatty acid is formed by a soluble desaturase......Page 374
Glycerol 3-phosphate is a precursor for the synthesis of glycerolipids......Page 377
The ER membrane is the site of fatty acid elongation and desaturation......Page 380
Some of the plastid membrane lipids are synthesized via the eukaryotic pathway......Page 381
Triacylglycerols are synthesized in the membranes of the endoplasmatic reticulum......Page 383
Plant fat is used for human nutrition and also as a raw material in industry......Page 384
Plant fats are customized by genetic engineering......Page 385
Storage lipids are mobilized for the production of carbohydrates in the glyoxysomes during seed germination......Page 387
The glyoxylate cycle enables plants to synthesize hexoses from acetyl CoA......Page 389
Reactions with toxic intermediates take place in peroxisomes......Page 391
Lipoxygenase is involved in the synthesis of oxylipins, which are defense and signal compounds......Page 392
Secondary metabolites often protect plants from pathogenic microorganisms and herbivores......Page 398
Plants synthesize phytoalexins in response to microbial infection......Page 399
Plant defense compounds can also be a risk for humans......Page 400
Alkaloids comprise a variety of heterocyclic secondary metabolites......Page 401
Some plants emit prussic acid when wounded by animals......Page 403
Some wounded plants emit volatile mustard oils......Page 404
Plants protect themselves by tricking herbivores with false amino acids......Page 405
A large diversity of isoprenoids has multiple functions in plant metabolism......Page 408
Acetyl CoA is a precursor for the synthesis of isoprenoids in the cytosol......Page 410
Pyruvate and D-glyceraldehyde-3-phosphate are the precursors for the synthesis of isopentyl pyrophosphate in plastids......Page 412
Prenyl transferases catalyze the association of isoprene units......Page 413
Some plants emit isoprenes into the air......Page 415
Many aromatic compounds derive from geranyl pyrophosphate......Page 416
Farnesyl pyrophosphate is the precursor for the synthesis of sesquiterpenes......Page 418
Steroids are synthesized from farnesyl pyrophosphate......Page 419
Oleoresins protect trees from parasites......Page 421
Carotene synthesis delivers pigments to plants and provides an important vitamin for humans......Page 422
A Prenyl chain renders compounds lipid-soluble......Page 423
Proteins can be anchored in a membrane by prenylation......Page 424
Dolichols mediate the glucosylation of proteins......Page 425
Isoprenoids are very stable and persistent substances......Page 426
Phenylpropanoids comprise a multitude of plant secondary metabolites and cell wall components......Page 429
Phenylalanine ammonia lyase catalyzes the initial reaction of phenylpropanoid metabolism......Page 431
Monooxygenases are involved in the synthesis of phenols......Page 432
Phenylpropanoid compounds polymerize to macromolecules......Page 434
Lignans act as defense substances......Page 435
Lignin is formed by radical polymerization of phenylpropanoid derivatives......Page 436
Suberins form gas- and water-impermeable layers between cells......Page 438
Some stilbenes are very potent natural fungicides......Page 440
Flavonoids have multiple functions in plants......Page 442
Anthocyanins are flower pigments and protect plants against excessive light......Page 444
Tannins bind tightly to proteins and therefore have defense functions......Page 445
Multiple signals regulate the growth and development of plant organs and enable their adaptation to environmental conditions......Page 448
G-proteins act as molecular switches......Page 449
Small G-proteins have diverse regulatory functions......Page 450
Ca2+ is a component of signal transduction chains......Page 451
The phosphoinositol pathway controls the opening of Ca2 channels......Page 452
Calmodulin mediates the signal function of Ca2 ions......Page 454
Phosphorylated proteins are components of signal transduction chains......Page 455
Phytohormones contain a variety of very different compounds......Page 457
Auxin stimulates shoot elongation growth......Page 458
Gibberellins regulate stem elongation......Page 461
Cytokinins stimulate cell division......Page 464
Abscisic acid controls the water balance of the plant......Page 466
Ethylene makes fruit ripen......Page 467
Brassinosteroids control plant development......Page 469
Systemin induces defense against herbivore attack......Page 471
A small protein causes the alkalization of cell culture medium......Page 472
Defense reactions are triggered by the interplay of several signals......Page 473
Salicylic acid and jasmonic acid are signal molecules in pathogen defense......Page 474
Phytochromes function as sensors for red light......Page 476
Phototropin and cryptochromes are blue light receptors......Page 479
A plant cell has three different genomes......Page 483
In the nucleus the genetic information is divided among several chromosomes......Page 484
The DNA of the nuclear genome is transcribed by three specialized RNA polymerases......Page 487
The transcription of structural genes is regulated......Page 488
Promoter and regulatory sequences regulate the transcription of genes......Page 489
Small (sm)RNAs inhibit gene expression by inactivating messenger RNAs......Page 490
The transcription of structural genes requires a complex transcription apparatus......Page 491
The formation of the mature messenger RNA requires processing......Page 493
DNA polymorphism yields genetic markers for plant breeding......Page 497
Individuals of the same species can be differentiated by restriction fragment length polymorphism......Page 498
The RAPD technique is a simple method for investigating DNA polymorphism......Page 501
The polymorphism of micro-satellite DNA is used as a genetic marker......Page 503
Transposable DNA elements roam through the genome......Page 504
Viruses are present in most plant cells......Page 505
Retrotransposons are degenerated retroviruses......Page 508
Plastids possess a circular genome......Page 509
The transcription apparatus of the plastids resembles that of bacteria......Page 512
The mitochondrial genome of plants varies largely in its size......Page 513
Mitochondrial RNA is corrected after transcription via editing......Page 516
Male sterility of plants caused by the mitochondria is an important tool in hybrid breeding......Page 517
Protein biosynthesis occurs in three different locations of a cell......Page 523
Protein synthesis is catalyzed by ribosomes......Page 524
A peptide chain is synthesized......Page 525
The translation is regulated......Page 529
Proteins attain their three-dimensional structure by controlled folding......Page 530
The folding of a protein is a multistep process......Page 531
Proteins are protected during the folding process......Page 532
Chaperones bind to unfolded proteins......Page 533
Most of the proteins imported into the mitochondria have to cross two membranes......Page 536
The import of proteins into chloroplasts requires several translocation complexes......Page 539
Proteins are imported into peroxisomes in the folded state......Page 542
Proteins are degraded by proteasomes in a strictly controlled manner......Page 543
Biotechnology alters plants to meet requirements of agriculture, nutrition and industry......Page 547
A gene library is required for the isolation of a gene......Page 548
A gene library can be kept in phages......Page 550
A gene library can also be propagated in plasmids......Page 551
A clone is identified by antibodies which specifically detect the gene product......Page 553
A clone can also be identified by DNA probes......Page 555
Genes encoding unknown proteins can be functionally assigned by complementation......Page 556
Agrobacteria can transform plant cells......Page 558
The Ti plasmid contains the genetic information for tumor formation......Page 560
Ti-Plasmids are used as transformation vectors......Page 562
A new plant is regenerated after the transformation of a leaf cell......Page 565
Protoplasts can be transformed by the uptake of DNA......Page 567
Plastid transformation to generate transgenic plants is advantageous for the environment......Page 569
Selected promoters enable the defined expression of a foreign gene......Page 571
Genes can be turned off via plant transformation......Page 572
Plant genetic engineering can be used for many different purposes......Page 574
Plants are protected against some insects by the BT protein......Page 575
Plants can be protected against viruses by gene technology......Page 577
Nonselective herbicides can be used as a selective herbicide by the generation of herbicide-resistant plants......Page 578
Genetic engineering is used to produce renewable resources for industry......Page 579
Genetic engineering provides a chance for increasing the protection of crop plants against environmental stress......Page 580
The introduction of transgenic cultivars requires a risk analysis......Page 581
Index......Page 583