PlantPlantBiochemistryBiochemistry

Hans-Walter HeldtHans-Walter Heldtin cooperation with Fiona Heldtin cooperation with Fiona Heldt

A leaf cell consists of A leaf cell consists of severalseveral

metabolic compartmentsmetabolic compartments

1 1

Figure 1.1 ElectronFigure 1.1 Electronmicrograph of mesophyllmicrograph of mesophylltissue from tobacco. Intissue from tobacco. Inmost cells the large centralmost cells the large centralvacuole is to be seen (v)vacuole is to be seen (v)..

Between the cells are theBetween the cells are theintercellular gas spacesintercellular gas spaces

))igig ,( ,(which are somewhatwhich are somewhatenlarged by the fixationenlarged by the fixationprocess. c: chloroplast, cw:process. c: chloroplast, cw:cell wall, n: nucleus, mcell wall, n: nucleus, m::mitochondrion. (By D. Gmitochondrion. (By D. G..Robinson, HeidelbergRobinson, Heidelberg(.(.

Figure 1.2 Figure 1.2 Diagram of amesophyll cellDiagram of amesophyll cell..

1.11.1 The cell wall gives the plant cellThe cell wall gives the plant cellmechanical stabilitymechanical stability

Figure 1.3 Figure 1.3 Main constituents of the cell wallMain constituents of the cell wall..1.3A. 1.3A. CelluloseCellulose

1.3B. A hemicellulose1.3B. A hemicellulose

1.3C. Constituent of pectin1.3C. Constituent of pectin

Figure 1.4 Figure 1.4 Ca++ and Mg++ ions mediate Ca++ and Mg++ ions mediate electrostatic interactions between pectin strandselectrostatic interactions between pectin strands..

Figure 1.5 Figure 1.5 Cell wall of Cell wall of the green alga the green alga OocystisOocystissolitaria. The cellulosesolitaria. The cellulose

microfibrils are microfibrils are arranged in a layer arranged in a layer pattern, in which pattern, in which parallel layers are parallel layers are

arranged one above arranged one above the other. Freeze the other. Freeze etching. (By D. G. etching. (By D. G.

Robinson, Heidelberg.)Robinson, Heidelberg.)

Figure 1.6 Figure 1.6 Plasmodesmata connect neighboring cells to form a Plasmodesmata connect neighboring cells to form a symplast . The extracellular spaces between the cell walls form the symplast . The extracellular spaces between the cell walls form the

apoplast . Schematic representation. Each of the connections apoplast . Schematic representation. Each of the connections shown actually consists of very many neighboring plasmodesmatashown actually consists of very many neighboring plasmodesmata..

Figure 1.7 Figure 1.7 Diagram of a Diagram of a plasmodesm.plasmodesm. The plasma membrane of the The plasma membrane of the neighboring cells is connected neighboring cells is connected by a tubelike membrane by a tubelike membrane invagination. Inside this tube is invagination. Inside this tube is a continuation of the a continuation of the endoplasmic reticulum. endoplasmic reticulum. Embedded in the membrane of Embedded in the membrane of the ER and the plasma the ER and the plasma membrane are protein particles membrane are protein particles that are connected to each that are connected to each other. The spaces between the other. The spaces between the particles form the diffusion particles form the diffusion path of the plasmodesm. It is path of the plasmodesm. It is controversial whether a controversial whether a diffusion between the diffusion between the neighboring cells also takes neighboring cells also takes place via the ER lumen. place via the ER lumen. A. cross-sectional view of the A. cross-sectional view of the membranemembrane B. vertical view B. vertical view

1.21.2 Vacuoles have multiple Vacuoles have multiple functionsfunctions

1.31.3 Plastids have evolved from Plastids have evolved from cyanobacteriacyanobacteria

Figure 1.8 Figure 1.8 AAcyanobacterium cyanobacterium forms a forms a symbiosis with symbiosis with a host cella host cell..

Figure 1.9 Figure 1.9 Plastids occur in various differentiated forms.Plastids occur in various differentiated forms. AA. Proplastid from young primary leaves of . Proplastid from young primary leaves of Cucurbita Cucurbita pepo (courgette);pepo (courgette);BB. Chloroplast from mesophyll cell of tobacco. Chloroplast from mesophyll cell of tobaccoleaf fixed at the end of the dark period; leaf fixed at the end of the dark period;

C. C. Leucoplast: amyloplast from the root of Leucoplast: amyloplast from the root of Cestrum auranticum; Cestrum auranticum; D. D. Chromoplast from petals also of Chromoplast from petals also of C. auranticum. C. auranticum.

(By D. G. Robinson, Heidelberg.)(By D. G. Robinson, Heidelberg.)

Figure 1.10Figure 1.10 Scheme ofScheme of

the the differentiation differentiation of a proplastid of a proplastid

to a to a chloroplastchloroplast

Figure 1.11 Figure 1.11 The granaThe granastacks of the thylakoidstacks of the thylakoid

membranes are membranes are connected by tubes, connected by tubes,

forming a continuous forming a continuous thylakoid spacethylakoid space

(thylakoid lumen). (thylakoid lumen). (After Weier and (After Weier and Stocking, 1963.)Stocking, 1963.)

1.41.4 Mitochondria also result fromMitochondria also result fromendosymbiontsendosymbionts

Figure 1.12 Figure 1.12 Diagram of the structure of a Diagram of the structure of a mitochondrionmitochondrion..

1.5 Peroxisomes are the site of reactions1.5 Peroxisomes are the site of reactionsin which toxic intermediates are formedin which toxic intermediates are formed

Figure 1.13 Figure 1.13 In mitochondria inaginations of the inner membrane result in an enlargement In mitochondria inaginations of the inner membrane result in an enlargement of the membrane surface. The figure shows mitochondria in a barley aleurone cell.of the membrane surface. The figure shows mitochondria in a barley aleurone cell.

(By D. G. Robinson, Heidelberg.) (By D. G. Robinson, Heidelberg.)

Figure 1.14 Peroxisomes.Figure 1.14 Peroxisomes. A A. Peroxisomes from the mesophyll cells of tobacco. The proximity . Peroxisomes from the mesophyll cells of tobacco. The proximity of peroxisome (P), mitochondrion (M), and chloroplast (C) reflects of peroxisome (P), mitochondrion (M), and chloroplast (C) reflects

the rapid metabolite exchange between these organelles in the the rapid metabolite exchange between these organelles in the course of photorespiration (discussed in Chapter 7).course of photorespiration (discussed in Chapter 7).

B. B. Glyoxysomes from germinating cotyledons of Glyoxysomes from germinating cotyledons of Cucurbita pepo Cucurbita pepo (courgette).(courgette).

The lipid degradation described in section 15.6 and the accompanying The lipid degradation described in section 15.6 and the accompanying gluconeogenesis require a close contact between lipid droplets (L), gluconeogenesis require a close contact between lipid droplets (L),

glyoxysome (G), and mitochondrionglyoxysome (G), and mitochondrion (M).(M). (By D. G. Robinson, (By D. G. Robinson, Heidelberg.) Heidelberg.)

1.6 The endoplasmic reticulum 1.6 The endoplasmic reticulum and Golgi apparatus form a and Golgi apparatus form a

network for the distribution of network for the distribution of biosynthesis productsbiosynthesis products

Figure 1.15 RoughFigure 1.15 Roughendoplasmic reticulum, cross section (arrows) and tangential endoplasmic reticulum, cross section (arrows) and tangential

sections (arrowheads). The ribosomes temporarily attached to the sections (arrowheads). The ribosomes temporarily attached to the membrane occur as polysome complexes (ribosome + mRNA). membrane occur as polysome complexes (ribosome + mRNA).

Section from the cell of a maturing peacotyledon. (By D. G. Section from the cell of a maturing peacotyledon. (By D. G. Robinson, Heidelberg.)Robinson, Heidelberg.)

Figure 1.16 Figure 1.16 Scheme of the interplay between the endoplasmic Scheme of the interplay between the endoplasmic reticulum and the Golgi apparatus in the transfer of proteins from reticulum and the Golgi apparatus in the transfer of proteins from the ER to the vacuoles and in the secretion of proteins from the cellthe ER to the vacuoles and in the secretion of proteins from the cell..

Figure 1.17 Figure 1.17 Golgi apparatus (dictyosome) in the green alga Golgi apparatus (dictyosome) in the green alga Chlamydomonas reinhardii. Chlamydomonas reinhardii. C C = = cis side, t = trans side. cis side, t = trans side. Arrowheads point to the Arrowheads point to the trans Golgi network. The trans Golgi network. The swollen swollen endoplasmatic reticulum (ER) is typical for this cell. On the ER, ribosomes can be endoplasmatic reticulum (ER) is typical for this cell. On the ER, ribosomes can be

recognized, except in the area where vesicles bud off. (By D. G. Robinson, Heidelberg.)recognized, except in the area where vesicles bud off. (By D. G. Robinson, Heidelberg.)

Figure 1.18 Figure 1.18 Model of the structure of clathrincoated vesicles..Model of the structure of clathrincoated vesicles.. (A) 3a and 3b subunits of clathrin form a complex with three arms.(A) 3a and 3b subunits of clathrin form a complex with three arms. (B) From this a hexagonal and pentagonal lattice (the latter not shown here) is formed by (B) From this a hexagonal and pentagonal lattice (the latter not shown here) is formed by

polymerization and this formspolymerization and this forms (C) the coat. (From Kleinig and Sitte.)(C) the coat. (From Kleinig and Sitte.)

1.71.7 Functionally intact cell Functionally intact cell organelles canorganelles can

be isolated from plant cellsbe isolated from plant cells

Figure 1.19 Figure 1.19 Protocol Protocol

for the isolation for the isolation of functionally of functionally

intact intact chloroplastschloroplasts..

Figure 1.20 Figure 1.20 Particles are separated by density gradient Particles are separated by density gradient centrifugation according to their different densitiescentrifugation according to their different densities

1.81.8 Various transport processes Various transport processes facilitate the exchange of facilitate the exchange of

metabolites between different metabolites between different compartmentscompartments

Figure 1.21 Classification Figure 1.21 Classification of membrane transport processesof membrane transport processes..

1.91.9 Translocators catalyze the Translocators catalyze the specific transport of substrates specific transport of substrates

and products of metabolismand products of metabolism

Figure 1.22 Silicone oil filtering centrifugationFigure 1.22 Silicone oil filtering centrifugation

Figure 1.23Figure 1.23 By measuring the By measuring the

concentration concentration dependence of the rate dependence of the rate

of uptake for a of uptake for a substance it can be substance it can be

decided whether the decided whether the uptake occurs by uptake occurs by

nonspecific diffusion nonspecific diffusion through the membrane through the membrane

(A) or by specific (A) or by specific transport (B)transport (B)..

Figure 1.24 Antiport.Figure 1.24 Antiport.Diagram of twoDiagram of two

possibilities for the possibilities for the counterexchangecounterexchangeof two substrateof two substratemolecules (A, B). molecules (A, B).

1)Pingpong1)Pingpongmechanism: Amechanism: Atranslocator translocator

molecule catalyzes molecule catalyzes the transport ofthe transport of

A and B sequentially. A and B sequentially. 2) Simultaneous 2) Simultaneous

mechanism:mechanism:Aand B are Aand B are transportedtransported

simultaneously by simultaneously by two translocator two translocator

moleculesmoleculestightly coupled to tightly coupled to

each other. each other.

Figure 1.25 Figure 1.25 Octylglucoside, a glycoside composed from a-Dglucose Octylglucoside, a glycoside composed from a-Dglucose and octyl alcohol, is a mild nonionic detergent that allows and octyl alcohol, is a mild nonionic detergent that allows

membrane proteins to be solubilized from the membranes without membrane proteins to be solubilized from the membranes without being denaturedbeing denatured..

Figure 1.26 Figure 1.26 The trioseThe triosephosphate-phosphatephosphate-phosphate

translocator from spinach translocator from spinach forms six transmembraneforms six transmembrane

helices. Each circlehelices. Each circlerepresents one amino represents one amino

acid. The likely positions acid. The likely positions of the transmembrane of the transmembrane helices were evaluated helices were evaluated

from the hydrophobicity from the hydrophobicity of the single amino acid of the single amino acid

residues. residues. The amino acids, markedThe amino acids, marked

with red, containing awith red, containing apositive charge in helix 5, positive charge in helix 5, represent an arginine and represent an arginine and

a lysine. These amino a lysine. These amino acids probably provide acids probably provide the binding sites for the the binding sites for the anionic substrates of the anionic substrates of the

triose phosphate-triose phosphate-phosphate translocator. phosphate translocator. (Data from Flügge et al., (Data from Flügge et al.,

1989.)1989.)

1.101.10 Ion channels have a very Ion channels have a very high transport capacityhigh transport capacity

Figure 1.27 Measurement of ion channel Figure 1.27 Measurement of ion channel currents by the “patch clamp” techniquecurrents by the “patch clamp” technique

Figure 1.28 Measurement of single channel currents of Figure 1.28 Measurement of single channel currents of the K+ outward channel in the K+ outward channel in a patch (Fig. 1.27) of the a patch (Fig. 1.27) of the

plasma membrane of guard cells from plasma membrane of guard cells from Vicia faba. (Outer Vicia faba. (Outer medium 50mM K+, cytoplasmic side 200mM K+, voltage medium 50mM K+, cytoplasmic side 200mM K+, voltage

+35mV.) (Data from Prof. G. Thiel, Darmstadt.)+35mV.) (Data from Prof. G. Thiel, Darmstadt.)

It has long been known that the channel protein is built from two identical It has long been known that the channel protein is built from two identical subunits, each of which has two transmembrane helices connected by subunits, each of which has two transmembrane helices connected by

a sequence of about 30 amino acids (loop) (Fig. 1.29A).a sequence of about 30 amino acids (loop) (Fig. 1.29A).

Structure analysis showed that a K+ channel is built of four of theseStructure analysis showed that a K+ channel is built of four of thesesubunits (Fig. 1.29B, C).subunits (Fig. 1.29B, C).

1.111.11 Porins consist of Porins consist of ββ--sheet structuressheet structures

Figure 1.30 Measurement of the size of a Figure 1.30 Measurement of the size of a porin apertureporin aperture

Figure 1.31Figure 1.31 With With ββ-sheet -sheet

conformation the conformation the amino acid residues amino acid residues

of a peptide chain are of a peptide chain are arranged alternately arranged alternately

in front of and behind in front of and behind the surface of the the surface of the

sheetsheet..

Figure 1.32 Diagram of the structure of a membrane Figure 1.32 Diagram of the structure of a membrane pore formed by a porin. pore formed by a porin.

Figure A shows the view from aboveFigure A shows the view from above

figure B shows a cross section through the membrane. figure B shows a cross section through the membrane. Sixteen Sixteen ββ-sheet sequences of the porin molecules, each 13 amino -sheet sequences of the porin molecules, each 13 amino

acids long, form the pore. acids long, form the pore. The amino acid residues directed toward The amino acid residues directed toward the the membrane side of the pore have hydrophobic character; those membrane side of the pore have hydrophobic character; those

directed to the aqueous pore are hydrophilicdirected to the aqueous pore are hydrophilic..

The use of energy from sunlightThe use of energy from sunlightby photosynthesis is the basis of by photosynthesis is the basis of

life on earthlife on earth

22