Summary
The surface of turgid, nitrogen-fixing soybean root nodules is found to contain a number of prominent ridges on an otherwise smooth surface. Using the technique of critical point drying for tissue preparation, and scanning electron microscopy, these ridges were found to be lenticels, whose function is to permit the free movement of gases into and out of the nodule. The surface of the nodule between the lenticels contained no intercellular air spaces. The lenticels develop from a phellogen situated distal to a ring of sclereid cells in the nodule cortex. They develop as distinct “bands” of tissue immediately above and closely following the nodule vascular traces.
When the nodules are subjected to conditions of water stress or waterlogging the most significant change to their surface is associated with the lenticels. In water stressed nodules the lenticel tissue collapses quickly, followed closely by shrinkage and collapse of the epidermis and outer cortex. In waterlogged nodules the lenticel tissues develop extensively with the production of large masses of loosely packed cells.
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Pankhurst, C.E., Sprent, J.I. Surface features of soybean root nodules. Protoplasma 85, 85–98 (1975). https://doi.org/10.1007/BF01567760
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DOI: https://doi.org/10.1007/BF01567760