1. The Assimilation of Sulfur
Card Set Information
1. The Assimilation of Sulfur
PMB 135 exam5
plant physiology and biochemistry exam 5
What is the effect of sulfur deficiency?
: sulfur is an essential
for plant growth and plants show
when it is deficient
How do plants acquire sulfur?
soil as sulfat
e through the roots
is transported through plants
absorb sulfur dioxide
from the atmosphere by absorption through the leaf surface
What is the role of air pollution in sulfur nutrition?
accumulation of sulfur from air pollution
burning of fossil fuels
Roles of cysteine and methionine
sulfur-containing amino acids
: sulfur is used to synthesize cys and met
animals and humans are unable to reduce sulfur - require from diet
: cys is essential for met synthesis, critical components of proteins
- play critical roles in
structural and catalytic functions
cysteine is essential for forming thiol compounds
glutathione and phytochelatin
important for forming disulfide bonds
oxidizing the thiol groups
of two cys residues, oxidation by NADP+
involved in establishing tertiary and quaternary protein structures
structure and functions of glutathione
major end product - present in mM
protects cells from
- for every one mole of oxidized glutathione (GSSG), one mole of NADPH is required to reduce GSSG -> GSH
transport and storage
response to environmental stresses
glutathione peptides - form thiolate coordination complexes with heavy metals
low molecular weight phytochelatin-Cd complexes -
detoxify toxic metals
by binding the metal ions using the thiol groups as the ligand, transported into the vacuole by an ABC transporter
high molecular weight phytochelatin-Cd complexes - withing the vacuoule, includes the low molcular weight complex and Cd (brought in by antiporter) and sulfide
Cd sulfide crystallite - phytochelatins hold Cd in an ordered structure
In what other ways is S important?
How is S important in food flavor?
- sulfur compounds add flavors to food products, garlic, onions
in the vacuole - acts on alliin in the cytosol
produces flavor - mixing the enzyme with the substrate produces allicin
Which S compounds are involved in pathogen defense?
- deters herbivores, antimicrobial agent
- defend plants against pathogen attacks, especially fungi like camalexin
- plant glycosides that break down to release volatile defense substances isothiocyanates and nitriles
other roles for glucosinolates
properties of some vegetables like broccoli
like mustard, horseradish
In what ways is DMSP important?
1. osmoprotectant - helps against osmotic stress
2. cryoprotectant - protects from freezing damage
3. climate-regulating mechanism
4. repellent against plankton herbivores
How is DMSP involved in climate regulation?
: phytoplankton may regulate climate,
is broken down to
DMS moves into atmosphere and is oxidized to sulfate, leads to cloud formation
clouds lead to cooling, sulfate is dissolved in rain, returns to ocean
cloud cover reduces growth of phytoplankton