Why are Spartina grasses so successful? Adaptations to anoxia and hydrogen sulfide - PowerPoint PPT Presentation

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Why are Spartina grasses so successful? Adaptations to anoxia and hydrogen sulfide

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  1. Why are Spartina grasses so successful? Adaptations to anoxia and hydrogen sulfide Ray Lee and Brian Maricle School of Biological Sciences Washington State University

  2. 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.

  3. Why are physiological studies of Spartina relevant? • Physiological processes are the link between environment and performance Metabolic Structural adaptations Growth reproduction Challenges opportunities Physiological processes Performance Environment

  4. Spartina are physiologically resilient and vigorous • Physiological tolerance • Wide range of salinities • Waterlogged soils • Anoxia • Hydrogen sulfide

  5. Distribution of hydrogen sulfide in sediments Oxidized zone No hydrogen sulfide Anoxic zone Hydrogen sulfide-rich

  6. 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

  7. Chemoautotrophic symbiosis • An adaptation to exploit sulfide-rich environments

  8. Tolerating anoxic sediments • Aerenchyma • Anaerobic metabolism • Alcohol dehydrogenase • Sulfide oxidation Spartina anglica root

  9. Functions of aerenchyma • Oxygen transport • Reduce cellular oxygen demands

  10. Root Ultrastructure 1 cm from root tip 2 cm from root tip

  11. Root Ultrastructure 4 cm from root tip 6 cm from root tip

  12. Root Ultrastructure 8 cm from root tip 10 cm from root tip

  13. The difference in root structure between treatments of Spartina alterniflora

  14. A comparison of root structure between treatments of Spartina anglica

  15. S. anglica respirometry experiments • Use automated flow-through respirometry system • Investigate oxygen transport

  16. Flow-through respirometry

  17. Root - high O2 uptake mitochondria O2 Root surface O2 O2 High oxygen consumption and/or low aerenchyma supply

  18. Root - low O2 uptake mitochondria O2 Root surface O2 O2 O2 O2 Low oxygen consumption and/or high aerenchyma supply

  19. Oxygen transport is more effective in S. anglica compared with S. alterniflora

  20. 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.

  21. Differences in oxygen transport between species Negative fluxes=uptake; positive fluxes=release; n=9, 11, 9, 9

  22. Sulfide volatilization mitochondria H2S Root surface H2S Occurs in S. anglica but not S. alterniflora

  23. 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

  24. 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?

  25. Acknowledgements • J. Doeller and D. Kraus (UAB) • S. Hacker (WSU Vancouver) • Kim Patten (WSU Long Beach) • Miranda Wecker • NSF, NOAA, WSU faculty seed grant

  26. Sox mechanism H2S Enzyme or Metal catalyst Root surface O2 O2 O2 mitochondria SOx

  27. Spartina alterniflora roots catalyze the oxygenation of sulfide