PLANT PHYSIOLOGY , Vol 108, Issue 4 1455-1460, Copyright © 1995 by American Society of Plant Biologists
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WHOLE PLANT, ENVIRONMENTAL, AND STRESS PHYSIOLOGY |
A Short-Term Decrease in Nitrogenase Activity (C2H2 Reduction) Is Induced by Exposure of Soybean Shoots to Their CO2 Compensation Point
R. Vidal, A. Gerbaud, D. Vidal and J. J. Drevon
Laboratoire de Recherche sur les Symbiotes des Racines, Institut National de la Recherche Agronomique, Place Viala, 34060 Montpellier, France (R.V., A.G., J.-J.D.)
Photosynthesis and nitrogenase acetylene-reducing activity (ARA) were
measured in soybeans (Glycine max [L.] Merr.) in which the shoots were
exposed for 48 h to 60 [mu]L L-1 CO2, a value corresponding to their CO2
compensation point. Six hours after the beginning of the light period at
low CO2, the ARA started to decrease, reaching a rate of 50% of the control
rate in 14 to 24 h and 20% of the control rate in 34 to 38 h after the
beginning of the CO2 treatment. At these times, there was no net
photosynthesis, and the transpiration rate was 20% lower than that in the
control plants. An increase in the partial pressure of O2 around the
nodules alleviated this inhibition of ARA. The maximal ARA achieved at 40
kPaO2 was 3 times higher than that at 20 kPa O2 and similar to the maximal
ARA of the control plants. It was argued that the decrease in ARA of
soybean exposed to the CO2 compensation point was due to a decrease in the
nodule's permeability to O2 diffusion.
