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Related Experiment Videos

Nitrate and Nitrite Reduction by Wolffia arrhiza.

J A Swader1, C R Stocking

  • 1Botany Department, University of California, Davis, California 95616.

Plant Physiology
|February 1, 1971
PubMed
Summary

Intact Wolffia arrhiza chloroplasts can use nitrite but not nitrate for electron transport, reducing it to ammonia. Nitrite reduction requires intact chloroplasts and does not involve nitrate reductase.

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Area of Science:

  • Plant Physiology
  • Biochemistry
  • Photosynthesis

Background:

  • Chloroplasts are vital organelles for photosynthesis in plants.
  • Nitrate and nitrite are key nitrogen compounds involved in plant metabolism.
  • Understanding enzyme localization and function within chloroplasts is crucial for plant science.

Purpose of the Study:

  • To investigate the presence and activity of nitrate reductase in isolated Wolffia arrhiza chloroplasts.
  • To determine the role of intact chloroplasts in nitrite and nitrate reduction.
  • To elucidate the electron transport pathways involving nitrite in chloroplasts.

Main Methods:

  • Aqueous isolation of partially purified, intact chloroplasts from Wolffia arrhiza.
  • Assay of light-stimulated electron transport using nitrite or nitrate as electron acceptors.
  • Measurement of oxygen evolution and nitrite disappearance.
  • Osmotic shock to rupture chloroplasts and assess nitrite reduction.

Main Results:

  • Nitrate reductase was not detected in or associated with intact Wolffia arrhiza chloroplasts.
  • Intact chloroplasts utilized nitrite, but not nitrate, as an electron acceptor during light-stimulated electron transport.
  • Oxygen evolution (1.5 moles O2/mole nitrite) indicated nitrite reduction to ammonia.
  • Ruptured chloroplasts lost the ability to reduce nitrite without additional components.

Conclusions:

  • Nitrate reductase is likely absent from the chloroplasts of Wolffia arrhiza.
  • Intact chloroplasts possess the machinery for nitrite reduction to ammonia, independent of cytoplasmic factors.
  • The integrity of the chloroplast is essential for nitrite reduction during photosynthesis.

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