Respiration and the Energy Requirement for Nitrogen Fixation in Nodulated Pea Roots

Respiration and the Energy Requirement for Nitrogen Fixation in Nodulated Pea Roots Pisum sativum L. cv. Trapper plants were inoculated and grown in a controlled environment on N-free nutrient solution. After 4 weeks N was supplied to treatment plants as NH 4 NO 3 , KNO 3 , or NH 4 Cl and rates of C 2 H 2 reduction, root + nodule respiration, and leaf photosynthesis were determined 1 week later. The increase in respiration per unit of C 2 H 2 reduction was not affected by either the form of N added or the light conditions during growth, although the basal respiration rate with no C 2 H 2 reduction increased with irradiance level. The mean regression coefficient from plots of respiration versus C 2 H 2 reduction was 0.23 + 0.04 ( P (unk) .01) mg of CO 2 (μmol of C 2 H 2 reduced) −1 which was very similar to the value for the coefficient of respiration associated with nitrogenase activity estimated by subtracting growth and maintenance respiration. Since the rate of N accumulation in N-free nutrient conditions was proportional to the rate of C 2 H 2 reduction, it appears that the method gives a true estimate of the energy requirements for N fixation which for these conditions was equivalent to 17 grams of carbohydrate consumed per gram of N fixed. http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png

Respiration and the Energy Requirement for Nitrogen Fixation in Nodulated Pea Roots

Dec 1, 1977

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Publisher
American Society of Plant Biologist
Copyright
Copyright © 1977 by the American Society of Plant Biologists
ISSN
1532-2548
eISSN
0032-0889
DOI
10.1104/pp.60.6.817
Publisher site
See Article on Publisher Site

Abstract

Pisum sativum L. cv. Trapper plants were inoculated and grown in a controlled environment on N-free nutrient solution. After 4 weeks N was supplied to treatment plants as NH 4 NO 3 , KNO 3 , or NH 4 Cl and rates of C 2 H 2 reduction, root + nodule respiration, and leaf photosynthesis were determined 1 week later. The increase in respiration per unit of C 2 H 2 reduction was not affected by either the form of N added or the light conditions during growth, although the basal respiration rate with no C 2 H 2 reduction increased with irradiance level. The mean regression coefficient from plots of respiration versus C 2 H 2 reduction was 0.23 + 0.04 ( P (unk) .01) mg of CO 2 (μmol of C 2 H 2 reduced) −1 which was very similar to the value for the coefficient of respiration associated with nitrogenase activity estimated by subtracting growth and maintenance respiration. Since the rate of N accumulation in N-free nutrient conditions was proportional to the rate of C 2 H 2 reduction, it appears that the method gives a true estimate of the energy requirements for N fixation which for these conditions was equivalent to 17 grams of carbohydrate consumed per gram of N fixed.

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