2. Uptake and Transport of Sulfur

  1. global overview
    • sulfate permease - symporter, sulfate ions are taken up into root cells
    • cytosol -> plastids where sulfide reduced to form cysteine
    • or sulfate is stored in vacuole, transported through the xylem to the leaf
    • sulfate to leaf cytosol - once inside the leaf, sulfate may enter the leaf mesophyll cell through sulfate-permease in the plasma membrane
    • chloroplast sulfate reduction - sulfate transported from cytosol into the choloroplast where reduced to sulfide from cys and glutathione
    • export of glutathione - from chloroplast into the cytosol then into the phloem for transport back to the root
    • export of sulfide - S may also flow from the cholorplast to the mitochondria in the form of sulfide
  2. Is there one or multiple sulfate transporters?
    • multiple transporters
    • high affinity isoform - in roots
    • low affinity isoform - leaf cell
  3. Mechanism of sulfate uptake across the plasma membrane and into root cells?
    • sulfate permease - sulfate transporter
    • permease structure - single polypeptide chain with 12-membrane spanning regions
    • permease functioning - symporter, co-transporting sulfate with protons
    • proton gradient - produced by proton-pumping ATPas
  4. transport into the vacuole
    • uniporter - transport a single solute across the membrane
    • driven by a proton gradient from a tonoplast proton ATPase
    • driven by electrical gradient
  5. transport into plastids from root to leaf
    • proton-sulfate cotransporter
    • triose phosphate translocator
    • major species of sulfur transported is sulfate
  6. What are the main steps of the reductive sulfate assimilation pathway?
    • Part 1: activation of sulfate
    • Part 2: reduction of activated sulfate to sulfide
    • Part 3: formation of cysteine from sulfide
    • Part X: formation of methionine from cysteine

    • sulfate to sulfide - requires a lot of energy
    • 1) photosynthesis - choloroplasts
    • 2) oxidative pentose phosphate pathway - roots
Card Set
2. Uptake and Transport of Sulfur
plant physiology and biochemistry exam 5