Aerenchyma develops by cell lysis in roots AND CELL SEPARATION IN LEAF PETIOLES IN Sagittaria lancifolia (Alismataceae)

Aerenchyma gas spaces are important for plants that survive flooding because these spaces provide an internal pathway for oxygen transport to the root zone. The objective of this study was to characterize the development of aerenchyma gas spaces in Sagittaria lancifolia L., a dominant species in freshwater wetlands adjacent to the Gulf of Mexico. Tissue at different developmental stages was collected from hydroponically grown plants, embedded in plastic, and sections were observed with a light microscope. In S. lancifolia roots, lysigeny (cell lysis) produced gas spaces that increased in volume from the root meristem to the most mature root tissue. Shoot aerenchyma occurred in the large petioles of S. lancifolia and through the blade midrib, but not in the laminar portion of the blade. In contrast to the roots, gas spaces in the petiole were formed by schizogeny (cell separation during development). Shoot initials produced cells that formed interlocking cylinders in the cortex and diaphragm cells that bridged the central portion of the cylinders. Division and expansion of both these cell types increased the diameter of the cylinders and created schizogenous gaps between diaphragm layers that produced large gas spaces in mature tissue. Therefore, aerenchyma development occurs by two different processes in S. lancifolia.