Scanning electron microscopy analysis of the aerenchyma in two rice cultivars

The anatomy and construction of the aerenchyma of two different rice cultiv ars that differed in gas transport capacity through the aerenchyma was stud ied by scanning electron microscopy in different parts of the rice plants ( root, root-shoot transition, leaf sheath, leaf blade, and stem), with speci al emphasis to limitations of gas transport within the plant and gas exchan ge between the aerenchyma and the soil or the aerenchyma and the atmosphere . Differences in the construction or aerial extend of the aerenchyma betwee n the two cultivars were not observed. Measurements of CH4-concentrations w ithin the aerenchyma of the leaf sheaths and the internodes of the stem, as well as of the aerial extend of the aerenchyma indicate that CH4 is releas ed from rice aerenchyma to the atmosphere mainly via the leaf sheet. Appare ntly, the parenchymous cell layer that separates root and shoot aerenchyma provides the major resistance to gas transport within the rice plant. Furth er studies are required to identify features of this cell layer that mediat e differences in gas transport resistance.