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Root respiration associated with nitrate assimilation by cowpea
1Boyce Thompson Institute, Ithaca, New York 14853.
Plant Physiology
|August 1, 1986
Summary
Nitrate uptake by cowpea roots significantly increases respiration, indicating a substantial energy cost for nitrogen assimilation. This energy demand is light-dependent and comparable to costs of symbiotic nitrogen fixation.
Area of Science:
- Plant Physiology
- Plant Nutrition
- Biochemistry
Background:
- Nitrate assimilation is a crucial process for plant growth.
- Understanding the energy cost of nitrate uptake is vital for optimizing crop yields.
- Cowpea (Vigna unguiculata) is an important legume crop globally.
Purpose of the Study:
- To quantify the energy cost associated with nitrate (NO3-) uptake and assimilation in cowpea roots.
- To investigate the influence of light on the respiratory response to nitrate.
- To compare the energy cost of nitrate assimilation with other nitrogen acquisition pathways.
Main Methods:
- Nitrate uptake was measured using stable isotope (15)NO(3)-.
- Root respiration was quantified using respirometry.
- Experiments involved varying nitrate availability and light conditions for cowpea seedlings.
Main Results:
- Nitrate addition (10 millimolar) increased root respiration by 20-30% within 6 hours.
- This respiratory increase was dependent on light conditions, being absent when shoots were in the dark.
- The energy cost of nitrate assimilation was estimated at 2.3 grams of Carbon per gram of Nitrogen.
- This cost is comparable to theoretical estimates for nitrate assimilation and symbiotic N(2) fixation.
Conclusions:
- Nitrate uptake and assimilation represent a significant energy investment for cowpea plants.
- Light plays a critical role in fueling the respiratory demands of nitrate assimilation.
- The energy cost of assimilating nitrate is energetically similar to that of symbiotic nitrogen fixation in legumes.