Cytological aspects during the stretching of collapsed cells in the root aerenchyma of Potamogeton polygonus Cham. & Schltdl. (Potamogetonaceae)

Abstract

Aerenchyma tissue presents large air spaces with important physiological and ecological implications. Aerenchyma tissue enables the circulation and storage of gases in response to waterlogging and flooding. Although collapsed cells are usually identified as characteristic of lysigenous aerenchyma, organelles have been found in these cells in other aquatic species. Cell walls have also been implicated in cellular adhesion/separation. Therefore, the formation of a constitutive aerenchyma as in Potamogeton polygonus was investigated based on the glycan distribution and cytological aspects of collapsed cells. The interrelatedness of cell wall properties and aerenchyma formation have given new insights into aerenchyma formation, as a response to different plant habits. We investigated the cytological aspects of these cells via light and electron microscopy. We also performed immunolabeling experiments with a range of glycan-directed monoclonal antibodies to detect possible cell wall polymer changes in this tissue. P. polygonus presents a schizo-radial lysigenous type of aerenchyma in the roots. The lysigeny process did not involve middle lamella degradation. Highly methyl-esterified pectin labeled with LM20 is lost in the cell walls of collapsed cells, which could affect cell adhesion and morphology, leading to the stretching of aerenchyma cells. In contrast, labeling with LM19 (low methyl-esterified pectin) is increased in the anticlinal cell walls and middle lamella of aerenchyma cells. Beyond their known adhesion/separation properties, pectic polysaccharides might play an important role during the stretching of the collapsed cells. The relation of cell wall composition between induced/constitutive aerenchyma and habit indicates different glycan distribution among species.