Cortical Air Spaces (Aerenchyma) in Roots of Corn Subjected to Oxygen Stress

When the seminal root system of 14-day-old corn (Zea mays cv. Dekalb 202) was subjected to O(2) stress, nodal roots with well developed cortical air spaces (aerenchyma) grew into the deoxygenated solution. Microscopic examination showed that there was extensive breakdown of cells in the midcortex of these roots, while the stele, endodermis, and inner layer of cortical cells remained complete, as did the outer layers of the cortex and the epidermis. Occasional files of intact cells, and the wall residues of collapsed cells, crossed the space between inner and outer cortex. Experiments with short, intact root segments with and without air spaces showed that in the presence of O(2) the ability to absorb and translocate (86)Rb(+), per unit volume or length of root, was little affected by cortical degeneration. The distribution across root sections of recently supplied strontium and rubidium, determined by electron microprobe analysis, indicated that in roots with air spaces the strands of wall residues bridging the cortex could be involved in maintaining the conduction of ions from the outer cortex up to the endodermis.