Structural changes in the innercortex cells of soybean root nodules are induced by short‐term exposure to high salt or oxygen concentrations

ABSTRACT After a 2 h exposure of intact soybean nodules to high concentrations of NaCl (100mol m −3 ) or oxygen (8OkPa O 2 ), morphometric computations carried out using an image analysis technique on semi‐thin sections showed that both treatments induced a decrease in the area of the inner‐cortex cells, which were then characterized by a tangential elongation. In contrast, no significant change in area occurred in the middle‐cortex cells although their elongation decreased. Electron microscopic observations showed that in the inner‐cortex cells changes included the presence of wall infoldings, an enlarged periplasmic space and a lobate nucleus whose chromatin distribution differed from that of the control. Structural changes also occurred in the endoplasmic reticulum, microbodies, mitochondria and plastids. From several of these changes, which are similar to those noted in osmocontractil cells in response to external stimuli, it can be hypothesized that the inner cortex may provide a potential mechanism for the control of oxygen diffusion through the nodules.