Time-course of changes involved in the operation of the oxygen diffusion barrier in white lupin nodules
1995
Iannetta, P.P.M. | James, E.K. | Sprent, J.I. | Minchin, F.R.
Nodulated white lupins (Lupinus albus L. cv. Multolupa) were subject to either darkening for 12 h, followed by 24 h recovery in light, or to 50% O2 for 30 min. For each treatment, nodules were harvested at intervals for analysis by light and electron microscopy and determination of glycoprotein content using Enzyme Linked Immunosorbent Assays (ELISA). This allowed for an analysis of the sequence of events causing an increase in intercellular space occlusion within the inner cortex. The temporal sequence in response to darkening appears to be: (1) an initial rapid increase in the detectable levels of intracellular glycoprotein, due to either a state change or de novo synthesis, (2) a concomitant increase in the volume of thickened cell walls, causing a reduction of intercellular space volume and (3) after 1-3 h a release of glycoprotein into the intercellular space network of the inner cortex, accompanied (and possibly spread) by the continued constriction of the spaces due to cell wall and cell content expansion. The results for exposure to 50% O2 showed a similar, but much more rapid, sequence of events, operating within 15-30 min. The main difference between the two sequences was the lack of expansion of thickened cell walls with increased pO2. Also, it was possible to detect glycoprotein within cell walls following exposure to 50% O2 but not following darkening. These observations are discussed in relation to proposed mechanisms for the operation of a variable oxygen diffusion barrier in legume nodules.
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