Programmed cell death during aerenchyma formation in Typha angustifolia leaves

• The gas space of Typha angustifolia leaves is lysigenous aerenchyma.
• The lysigenous aerenchyma is caused by apoptotic-like PCD.
• The degradation of calcium oxalate crystals were observed during the PCD process.

To facilitate gas exchange, some plants produce specialized air cavities called aerenchyma. To determine how the aerenchyma is formed, we conducted serial experimental observations and tests. Here we provide evidence that aerenchyma is formed in Typha angustifolia leaves through cell lysis in which programmed cell death (PCD) is involved. We first observed by light microscopy that aerenchyma was formed by degradation of some specialized cells, the designated PCD-susceptible cells. Consistent with this observation, a TUNEL assay displayed the typical PCD features of in situ DNA fragmentation. The biomarkers of PCD were further revealed by gel electrophoresis. Using electron microscopy, we further observed that the PCD-susceptible cells underwent several organized changes that are typically associated with PCD, including emergence of vesicles, rupture of tonoplast, and degradation of cytoplasm, organelles, and cell walls. Additionally, we observed that calcium oxalate crystals appeared at the early cavity formation phase and disappeared at the late cavity formation phase during aerenchyma formation. Taken together, our results suggest that PCD plays a critical role in the development of lysigenous aerenchyma in T. angustifolia leaves.