Pectin Peek-a-Boo: Homogalacturonan Turnover During Flooding-Induced Legume Root Aerenchyma Formation

Flooding can cause root hypoxia and can lead to significant agricultural losses. Therefore, understanding plant adaptations to flooding, including root aerenchyma development, is one important avenue for insuring future global food security. We investigated cell wall modifications during root aerenchyma formation in response to the prolonged 0–48 h flooding of <i>Phaseolus coccineus</i>, <i>Pisum sativum</i>, and <i>Cicer arietinum</i> seedlings. Using transmission electron microscopy, toluidine blue O (TBO) staining, and immunolabeling with antibodies targeting de-methyl-esterified homogalacturonan (DMEH), partially DMEH, and methyl-esterified homogalacturonan (MEH), we examined changes in cell wall composition. Transmission electron microscopy and TBO staining revealed degradation of cell walls and middle lamella, with accumulation of DMEH near flooding-induced aerenchyma cavities. Immunolabeling indicated increased DMEH epitope availability in flooded roots, suggesting a role in cell wall remodeling. Enzyme pretreatments, used to “unmask” homogalacturonan by removing cellulose and hemicellulose, revealed that specific forms of homogalacturonan, particularly DMEH complexed with calcium and MEH, are masked by these cell wall components. The study highlights the complex interplay of pectin, cellulose, and hemicellulose in cell wall degradation during aerenchyma development, providing insights into legume flooding stress responses.