Minerální výživa rostlin 3 Ivan Šetlík Biologická fakulta Jihočeské Univerzity Katedra fyziologie a anatomie rostlin Kurz fyziologie rostlin Minerální výživa rostlin 3 Ivan Šetlík S2- S SO42-

chemoautotrofní a fotosyntetické sirné bakterie redukce (rostliny, mikroorganismy) disimilační redukce sulfátu (anaerobní bakterie) síranové estery polysacharidů, sulfatované steroidy atd. bílkoviny chemoautotrofní a fotosyntetické sirné bakterie živočichové, mikroorganismy oxidace

BMBP 16.56 Figure 16.56 Model for sulfate transport across the plasma membrane. The transport of sulfate is powered by an electrochemical proton gradient generated by an ATPase that extrudes protons to the cell exterior. The sulfate transporter is able to couple the influx of protons to the transport of sulfate into the cell.

BMBP 16.58 The permease-type sulfate transporter is a single polypeptide with 12 membrane spanning regions, characteristic of cation/solute co-transporter. It shares significant aminoacid sequence homology with H+/SO4 cotransporters from fungi and mammals. Plasma membrane sulfate transporters have widely different sulfate affinities and distinct expression patterns. A high affinity isoform is expressed exclusively in roots. It mediates sulfate uptake from soil water in which the concentration is low and variable. An isoform with a lower affinity is expressed predominantly in the leaves and mediates transport from the xylem cells or between subcellular compartments.

kořenová buňka Leukoplast nebo proplastid vakuola ATPáza čerpající protony síranová permeáza o vysoké aktivitě

mezofylová buňka listu sulfátované sloučeniny vakuola mitochondrie permeáza pro síran s nízkou aktivitou floém xylém

SO42– + ATP + 8 e– + 8 H+ = = S2– + 4 H2O + AMP + PPi

BMBP 16.59 The reaction catalyzed by ATP sulfurylase.

Syntéza APS sulfát + ATP  APS + PPi G0' = 45 kJ Syntéza APS sulfát + ATP    APS + PPi      G0' =  45 kJ.mol-1 spřažená s hydrolýzou pyrofosfátu PPi + H2O    2 Pi G0' = -33,5 kJ.mol-1 je stále ještě endergonická. Sdruží-li se se syntézou PAPS APS + ATP    PAPS + ADP         G0' = -25 kJ.mol-1 je úhrnná bilance příznivá

APS sulfotransferáza, používá APS jako donor sulfurylové skupiny a přenáší sulfát na akceptorovou thiolovou skupinu, patrně na glutathion. Vzniklý thiosulfonát redukuje na thiosulfid reduktáza thiosulfonátu, závislá na ferredoxinu. BMBP 16.60 Figure 16.60 Two hypotheses for sulfate reduction in plants. (A) Hypothesis 1. APS sulfotransferase, using APS as a sulfuryl donor, transfers sulfate to an acceptor thiol compound, possibly glutathione. The resulting organic thiosulfonate is reduced to thiosulfide by a ferredoxin-dependent thiosulfonate reductase. (B) Hypothesis 2. APS is first phosphorylated to PAPS by APS kinase. PAPS reductase then produces sulfite by using electrons donated from thioredoxin. Sulfite reductase then completes the reduction to sulfide by using electrons from ferredoxin.

APS kináza nejprve fosforyluje APS na PAPS APS kináza nejprve fosforyluje APS na PAPS. PAPS reduktáza použije elektrony z thioredoxinu na tvorbu sulfitu. Reduktáza sulfitu pak použije elektrony z ferredoxinu a dovede redukci až k sulfidu. BMBP 16.60 Figure 16.60 Two hypotheses for sulfate reduction in plants. (A) Hypothesis 1. APS sulfotransferase, using APS as a sulfuryl donor, transfers sulfate to an acceptor thiol compound, possibly glutathione. The resulting organic thiosulfonate is reduced to thiosulfide by a ferredoxin-dependent thiosulfonate reductase. (B) Hypothesis 2. APS is first phosphorylated to PAPS by APS kinase. PAPS reductase then produces sulfite by using electrons donated from thioredoxin. Sulfite reductase then completes the reduction to sulfide by using electrons from ferredoxin.

BMBP 16.60 Figure 16.60 Two hypotheses for sulfate reduction in plants. (A) Hypothesis 1. APS sulfotransferase, using APS as a sulfuryl donor, transfers sulfate to an acceptor thiol compound, possibly glutathione. The resulting organic thiosulfonate is reduced to thiosulfide by a ferredoxin-dependent thiosulfonate reductase. (B) Hypothesis 2. APS is first phosphorylated to PAPS by APS kinase. PAPS reductase then produces sulfite by using electrons donated from thioredoxin. Sulfite reductase then completes the reduction to sulfide by using electrons from ferredoxin.

Jeden z hlavních konečných produktů reduktivní asimilace sulfátu je glutathion. Je to hlavní nebílkovinný thiol v rostlinách. Jeho milimolární koncentrace v buňkách výrazně přesahují mikromolární koncentrace cysteinu. As a major endproduct of the reductive sulfate assimilation, glutathione is the major nonprotein thiol in plants, present in milimolar concentrations, that far exceed the micromolar conc. of cysteine. Is involved in the storage and long distance transport of reduced sulfur, in signal transduction pathways, in scavenging active oxygen species, in detoxifying xenobiotics and serving as a substrate for phytochelatin synthesis. Two enzymes make up the glutathione biosynthetic pathway - vide infra Glutathion se účastní skladování redukované síry a jejího transportu v rostlině, dále jako přenašeč v signálních drahách, dále zneškodňuje různé formy aktivního kyslíku, xenobiotika a slouží jako substrát pro syntézu fytochelatinů.

Homoglutathione (b-alanin je nahrazen Gly; je obsažen v některých luštěninách) Hydroxymethylglutathione (Ser je nahrazen Gly; je obsažen v některých travách) g-Glutamylcysteinylglutamate (Glu je nahrazen Gly;je osažen v kukuřici)

GSH = redukovaný glutathion herbicid GSH = redukovaný glutathion přenos GS-herbicid modifikace a uložení vakuola

Transpeptidizatio reaction catalyzed by phytochelatin synthase to produce (gama-Glu-Cys)nGly

Dvě fytochelatinové molekuly [(gama-Glu-Cys)2Gly] koordinované iontem kadmia. Fytochelatiny váží ionty těžkých kovů a odstraňují je z buněčného ústrojí. BMBP16.69A Two phytochelatin molecules [(y-Glu-Cys)2Gly] coordinated with an ion of cadmium. By binding toxic heavy metal ions, phytochelatins remove them from the cellular machinery. It is thought that the thiol groups of phytochelatins serve as the ligand for heavy metal ions.

Model znázorňuje mechanismus mineralizace a odloučení CdS v rostlinných buňkách zprostředkovaného fytochelatiny. BMBP 16.69B (B) A model for the mechanism of CdS mineralization and sequestration in plant cells mediated by phytochelatins. Both phytochelatins and low-molecular-weight (LMW) phytochelatin-Cd complexes formed in the cytosol enter the vacuole by way of an ABC transporter (1). Cd ions enter the vacuole by way of an antiporter in exchange for protons (2). HMW, high molecular weight. The electrochemical gradient across the tonoplast is maintained by a proton-pumping ATPase (3).

Gropup transfer coenzymes, vitamins, substrates

Allicin has antimicrobial and feeding deterrent activities Glucosinolates, sulfur containing defense compounds produced by a variety of plants: broccoli, mustards and horseradish Sinapis alba produces benzyl glucosinolate derivative sinapine

BMBP 16.55 Figure 16.55 The phytoplankton-climate connection. Phytoplankton-produced DMSP (dimethylsulfoniopropionate) is broken down by bacteria to DMS (dimethyl sulfide) and acrylate. (A) DMS volatilizes and is oxidized to DMSO and to sulfate, which nucleates water droplets, leading to cloud formation. (B) Sulfate is returned to the sea dissolved in rain. Because cloud cover reduces the growth of phytoplankton and is accompanied by atmospheric cooling, phytoplankton have been proposed to serve as a homeostatic climate regulation mechanism. The extent to which phytoplankton regulate climate is still being keenly debated. Dimethylsulfoniopropionate (DMSP) has many roles, e.g. osmoprotectant, cryoprotectant repellant against planctonic herbivores.

(A) Vztah fytoplanktonu ke klimatu (A) Vztah fytoplanktonu ke klimatu. Dimethyl- sulfoniopropionát (DMSP) rozkládají bakterie na dimethylsulfid (DMS) a akrylát. DMS vytěká do atmosféry, kde se oxiduje na dimethylsulfoxid (DMSD) a sulfát, který slouží jako kondenzační jádra pro vodu a tak se tvoří mraky. BMBP 16.55 Figure 16.55 The phytoplankton-climate connection. Phytoplankton-produced DMSP (dimethylsulfoniopropionate) is broken down by bacteria to DMS (dimethyl sulfide) and acrylate. (A) DMS volatilizes and is oxidized to DMSO and to sulfate, which nucleates water droplets, leading to cloud formation. (B) Sulfate is returned to the sea dissolved in rain. Because cloud cover reduces the growth of phytoplankton and is accompanied by atmospheric cooling, phytoplankton have been proposed to serve as a homeostatic climate regulation mechanism. The extent to which phytoplankton regulate climate is still being keenly debated. Dimethylsulfoniopropionate (DMSP) has many roles, e.g. osmoprotectant, cryoprotectant repellant against planctonic herbivores.

(B) Sulfát rozpuštěný v dešťových kapkách se vrací do moře (B) Sulfát rozpuštěný v dešťových kapkách se vrací do moře. Poněvadž oblačnost zpomaluje růst fytoplanktonu a působí ochlazení atmosféry, považuje se tento pochod za homeostatický mechanismus. Dimethylsulfoniopropionát (DMSP) má mnoho úloh, např. je osmoprotektantem, kryoprotektantem a odpuzuje planktonní herbivory. BMBP 16.55 Figure 16.55 The phytoplankton-climate connection. Phytoplankton-produced DMSP (dimethylsulfoniopropionate) is broken down by bacteria to DMS (dimethyl sulfide) and acrylate. (A) DMS volatilizes and is oxidized to DMSO and to sulfate, which nucleates water droplets, leading to cloud formation. (B) Sulfate is returned to the sea dissolved in rain. Because cloud cover reduces the growth of phytoplankton and is accompanied by atmospheric cooling, phytoplankton have been proposed to serve as a homeostatic climate regulation mechanism. The extent to which phytoplankton regulate climate is still being keenly debated. Dimethylsulfoniopropionate (DMSP) has many roles, e.g. osmoprotectant, cryoprotectant repellant against planctonic herbivores.