Responses of spinach leaf mitochondria to low N availability

Plant Cell Environ. 2006 Apr;29(4):710-9. doi: 10.1111/j.1365-3040.2005.01457.x.


Low N availability induces carbohydrate accumulation in leaf cells, which often causes suppression of photosynthesis. Under low N supply, excess carbohydrates would be preferentially respired by the non-phosphorylating pathways, such as the alternative oxidase (AOX) and uncoupling protein (UCP), which would suppress the excessive increase in the ratio of C to N (C/N ratio). In leaves, however, responses of these pathways to the low N stress are still unknown. We examined the mitochondrial respiratory pathways in spinach leaves grown at three different N availabilities to clarify whether the respiratory pathways change depending on the N availabilities. With the decrease in N availability, leaf respiratory rates per leaf area decreased, but the rates on the leaf N basis were comparable. Using fumarase activities of whole leaf extracts and isolated mitochondria, we estimated mitochondrial protein contents per leaf N. The contents increased with the decrease in the N availability, that is, at the low N availability, N was preferentially invested into mitochondria. On the mitochondrial protein basis, capacities of cytochrome pathway (CP) and cytochrome c oxidase (COX) were comparable regardless of the N availabilities, whereas both AOX capacity and the amounts of AOX protein increased with the decrease in the N availability. Some enzymes of tricarboxylic acid (TCA) cycle, especially NAD-dependent malic enzyme (NAD-ME), showed higher capacities under lower N. On the other hand, amounts of UCP did not differ amongst the N availabilities. These results indicated that, under low N stress, AOX will be preferentially up-regulated and will efficiently consume excess carbohydrates, which leads to suppressing the rise in the C/N ratio to a moderate level.

Publication types

  • Comparative Study
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Carbohydrate Metabolism
  • Carbon / metabolism
  • Citric Acid Cycle / physiology
  • Electron Transport / physiology
  • Electron Transport Complex IV / metabolism
  • Fumarate Hydratase / metabolism
  • Immunohistochemistry
  • Ion Channels / analysis
  • Ion Channels / metabolism
  • Mitochondria / metabolism*
  • Mitochondria / physiology
  • Mitochondrial Proteins / analysis
  • Mitochondrial Proteins / metabolism
  • Nitrogen / metabolism*
  • Oxidoreductases / analysis
  • Oxidoreductases / metabolism
  • Photosystem II Protein Complex / metabolism
  • Plant Extracts / chemistry
  • Plant Leaves / anatomy & histology
  • Plant Leaves / metabolism
  • Plant Leaves / physiology
  • Plant Proteins / metabolism
  • Spinacia oleracea / anatomy & histology
  • Spinacia oleracea / metabolism*
  • Spinacia oleracea / physiology
  • Uncoupling Protein 1


  • Ion Channels
  • Mitochondrial Proteins
  • Photosystem II Protein Complex
  • Plant Extracts
  • Plant Proteins
  • Uncoupling Protein 1
  • Carbon
  • Oxidoreductases
  • alternative oxidase
  • Electron Transport Complex IV
  • Fumarate Hydratase
  • Nitrogen