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Title: INHIBITION OF NITROGENASE ACTIVITY AND NODULE OXYGEN PERMEABILITY BY WATER DEFICIT

Author
item SERRAJ, RACHID - SEMLALIA, MOROCCO
item Sinclair, Thomas

Submitted to: Journal of Experimental Botany
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/18/1996
Publication Date: N/A
Citation: N/A

Interpretive Summary: Nitrogen fixation in soybean has been consistently shown to be sensitive to drought. The sequence of events that takes place when the nodules are subjected to drought has not been explored. This study presents data on nitrogen fixation rates, nodule respiration, and nodule response to increasing atmospheric oxygen in response to the rapid imposition of water deficits. The results showed that respiration declines shortly after the introduction of a water deficit treatment and that this was followed by a decrease in nodule respiration. Both factors could be fully restored within 4 h after treatment by increasing the oxygen concentration. After 24 h of exposure to the water deficit treatment, there was a substantial loss in respiration and nitrogen fixation, and in a failure of the nodules to respond to oxygen increases. These results showed that there is at least two distinct phases in the response of nodules to drought.

Technical Abstract: Short-term effects of water deficit on nitrogenase activity were investigated with soybean (Glycine max L.Merr. cv. Biloxi) by adding polyethylene glycol (PEG) to the hydroponic solution and measuring nitrogenase activity, nodule respiration, and permeability to oxygen diffusion (Po). These experiments showed a rapid decrease in acetylene reduction activity (ARA) and nodule respiration. A consequence of the decreased respiration rate was that Po calculated by Fick's Law also decreased. However, these results were in direct conflict with a previous report of stability in Po determined by using an alternative technique. To resolve this conflict, an hypothesis describing a sequence of responses to the initial PEG treatment is presented. An important finding of this study was that the response to water deficit induced by PEG occurred in two stages. The first stage was O2 limited and could be reversed by elevated pO2. The second stage which developed after 24 h of exposure to PEG resulted in substantial loss in nodule activity which could not be recovered with increased pO2. Severe water deficit disrupt nodule activity to such a degree that O2 is no longer the major limitation.