Transient Increase of Anaerobically-Induced Enzymes during Short-Term Drought of Alfalfa Root Nodules

Abstract

The effects of short-term drought stress on alfalfa (Medicago sativa cv. Aragon) root nodule nitrogenase activity and several carbon metabolic enzymes were studied over an 8 d period of withholding water. Nitrogenase activity was more severely affected by drought stress than any of the carbon metabolic enzymes measured. The overall decrease in acetylene reduction activity and protein content could be described by first order rate constants, which implied a general metabolic decline. However, expression and/or repression of carbon metabolic enzymes suggested that active and distinctive metabolic changes occurred during progressive drought stress. These changes in metabolism are consistent with a relative change in the level of oxygen within the nodule. The expression of the anaerobically-induced enzymes, alcohol dehydrogenase and malate dehydrogenase, during the initial phases of drought stress is consistent with anaerobiosis within the alfalfa nodule. Continued drought stress resulted in loss of activity of anaerobically-induced enzymes implying the return of a more aerobic environment, suggesting an adaptive response by the plant.