Transcript Why are Spartina grasses so successful? Adaptations to anoxia and hydrogen sulfide
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 Challenges opportunities Metabolic Structural adaptations Growth reproduction Environment Physiological processes 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 zone No hydrogen sulfide Anoxic zone Hydrogen 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 Ultrastructure 1 cm from root tip 2 cm from root tip
Root Ultrastructure 4 cm from root tip 6 cm from root tip
Root Ultrastructure 8 cm from root tip 10 cm from root tip
The difference in root structure between treatments of
Spartina alterniflora
40.00
35.00
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0.00
0 5 10 distance from root tip (cm) 15 B14-FL B16-DR B19-FL B44-DR B48-FL B54-FL B59-FL B60-FL B17-DR
A comparison of root structure between treatments of
Spartina anglica
40.00
35.00
30.00
25.00
20.00
15.00
10.00
5.00
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0 20 A11-FL A15-DR A16-DR A17-FL A53-DR A56-FL A57-FL A59-DR A64-FL A66-DR 5 10 distance from root tip (cm) 15
S. anglica
respirometry experiments • Use automated flow through respirometry system • Investigate oxygen transport
Flow-through respirometry
Root - high O 2 uptake O 2 Root surface O 2 O 2 mitochondria High oxygen consumption and/or low aerenchyma supply
Root - low O 2 uptake O 2 Root surface O O 2 2 O 2 O 2 mitochondria Low oxygen consumption and/or high aerenchyma supply
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 N 2 flushed water.
• An oxygen-sensing probe can be used to monitor the water--any increase in O 2 must have come through the plant.
Differences in oxygen transport between species Negative fluxes=uptake; positive fluxes=release; n=9, 11, 9, 9
Sulfide volatilization H 2 S Root surface H 2 S mitochondria Occurs in
S. anglica alterniflora
but not
S.
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 alterniflora
grow better than
S.
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
Sox mechanism H 2 S Root surface O 2 O 2 O 2 mitochondria Enzyme or Metal catalyst SO x
Spartina alterniflora
roots catalyze the oxygenation of sulfide