Why are Spartina grasses so successful? Adaptations to
anoxia and hydrogen sulfide
Ray Lee and Brian Maricle
School of Biological Sciences
Washington State University
Spartina alterniflora and Spartina anglica
• Saltmarsh grasses native to the Eastern U.S. (S. alterniflora) and British Isles (S. anglica).
• Invasive species in Puget Sound and Willapa Bay in Washington State.
Why are physiological studies of Spartina relevant?
• Physiological processes are the link between environment and performance
Environment
Challengesopportunities
MetabolicStructuraladaptations
Physiologicalprocesses
Growthreproduction
Performance
Spartina are physiologically resilient and vigorous
• Physiological tolerance – Wide range of salinities– Waterlogged soils
• Anoxia
• Hydrogen sulfide
Distribution of hydrogen sulfide in sediments
Oxidized zoneNo hydrogen sulfide
Anoxic zoneHydrogen sulfide-rich
Sulfide is a potent toxin to aerobic respiration
• µM levels inhibit mitochondrial cytochrome c oxidase
• Sulfide binds to hemoglobin forming sulfhemoglobin
• Sulfide spontaneously reacts with oxygen producing hypoxic/anoxic conditions
• Can be used as an energy source by sulfide-oxidizing bacteria
Chemoautotrophic symbiosis
• An adaptation to exploit sulfide-rich environments
Tolerating anoxic sediments
• Aerenchyma
• Anaerobic metabolism– Alcohol
dehydrogenase
• Sulfide oxidation
Spartina anglica root
Functions of aerenchyma
• Oxygen transport
• Reduce cellular oxygen demands
Root Ultrastructure1 cm from root tip 2 cm from root tip
Root Ultrastructure4 cm from root tip 6 cm from root tip
Root Ultrastructure8 cm from root tip 10 cm from root tip
The difference in root structure between treatments of Spartina alterniflora
A comparison of root structure between treatments of Spartina anglica
S. anglica respirometry experiments
• Use automated flow-through respirometry system
• Investigate oxygen transport
Flow-through respirometry
mitochondria
O2
O2
O2
Root surface
Root - high O2 uptake
High oxygen consumption and/or low aerenchyma supply
mitochondria
O2
O2
O2
Root surface
Root - low O2 uptake
Low oxygen consumption and/or high aerenchyma supply
O2
O2
Oxygen transport is more effective in
S. anglica compared with S. alterniflora
Checking for oxygen transport
• A plant can be sealed into a flask of N2-flushed water.
• An oxygen-sensing probe can be used to monitor the water--any increase in O2 must have come through the plant.
Differences in oxygen transport between species
Negative fluxes=uptake; positive fluxes=release; n=9, 11, 9, 9
mitochondriaH2S
H2S
Root surface
Sulfide volatilization
Occurs in S. anglica but not S. alterniflora
Conclusions
• Function of increased aerenchyma appears to be to reduce oxygen demands NOT increase oxygen transport
• S. anglica has a highly effective oxygen AND sulfide transport system
Questions
• Can S. anglica grow better than S. alterniflora in anoxic/sulfidic conditions?
• Can sulfide levels ever be so high that plants cannot deal with it?
• What is the relationship between sulfide levels and effectiveness of eradication efforts?
Acknowledgements
• J. Doeller and D. Kraus (UAB)
• S. Hacker (WSU Vancouver)
• Kim Patten (WSU Long Beach)
• Miranda Wecker
• NSF, NOAA, WSU faculty seed grant
mitochondria
O2
H2S
SOxO2
O2
Enzyme orMetal catalystRoot surface
Sox mechanism
Spartina alterniflora roots catalyze the oxygenation of sulfide
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