Effects of Water Stress on the Respiratory and Nitrogen-fixing Activity of Soybean Root Nodules

Response to Drought Stress of Nitrogen Fixation (Acetylene Reduction) Rates by Field-Grown Soybeans

“…The results of the 02 enrichment study with drought-stressed nodules are also in close agreement with those reported for detached nodules (12). Elevated levels of 02 increased the maximum flux density of acetylene and returned the activity of drought-stressed nodules to those associated with well-watered conditions.…”

“…If the initial effects of drought stress on nitrogen fixation are largely due to a decreased 02 permeability through the nodule cortex, elevated 02 concentrations in the atmosphere surrounding drought-stressed or dessicated nodules should result in a recovery of acetylene reduction rates. Such observations have been reported (12) for detached drought-stressed nodules. Ralston and Imsande (14) reported that the loss of nodule activity associated with nodule excision could be overcome by exposure to elevated concentrations of 02.…”

“…This is supported by the findings of Bennett and Albrecht (1) who found that nitrogen fixation was closely correlated with nodule water potential which, in turn, was more sensitive to drought stress than was either leaf water potential or diffusive conductance. Pankhurst and Sprent (11,12) postulated that the primary effect of drought stress on nitrogen fixation was to depress oxygen uptake and therefore respiration, causing a depletion of ATP inside the nodule. They presumed that the depressed oxygen uptake was caused by either a loss ofoxygen conductance through the nodule or by inhibition of oxygen requiring reactions, or perhaps by both.…”

Phosphorylation of Soybean Nodulin 26 on Serine 262 Enhances Water Permeability and Is Regulated Developmentally and by Osmotic Signals

“…In addition, nodule development and maintenance are extremely sensitive to environmental and metabolic stresses. Osmotic stress results in morphological and biochemical changes that lead to the rapid cessation of nitrogen fixation (Pankhurst and Sprent, 1975;Weisz et al, 1985;Serraj et al, 1994), the induction of genes involved in stress adaptation (Delauney and Verma, 1990), and the accumulation of compatible solutes such as Pro and sugars, presumably to restrict water loss (Kohl et al, 1991;Irigoyen et al, 1992). Changes in membrane permeability coordinated with the accumulation and compartmentation of compatible solutes may be part of the osmotic adjustment, aiding in the maintenance of cell turgor and redirecting tissue water flow toward critical cells (Bohnert et al, 1995).…”

“…Because calcium signaling has been implicated in plant responses to osmotic signals (Knight et al, 1997), and considering the high sensitivity of nodules to osmotic stress signals (Pankhurst and Sprent, 1975;Weisz et al, 1985;Serraj et al, 1994), the effects of salinity stress on nodulin 26 phosphorylation in mature nodules were addressed. Exposure of 33-dayold nodulated soybeans to saline conditions (0.3 M NaCl) resulted in no detectable change in the overall levels of nodulin 26 protein ( Figure 9A, anti-nodulin 26 signal), whereas the phosphorylation levels of the protein ( Figure 9B, anti-GC12P signal) were enhanced as early as 4 h after treatment and remained high at 24 h after stimulus.…”