When we think of development in biology, we probably first think about the processes of cell division, tissue, and organ formation. In many cases though, for an organ to develop, cells and entire tissues have to die. This process is known as Programmed Cell Death (PCD).

Cross section of a young root of sugarcane.
Cross section of a young root of sugarcane. The top third of the figure shows the region where the aerenchyma is fully formed. Note the presence of trabeculae formed by a composite. They are made of cell walls that collapse after cell death and connect the vascular cylinder to the epidermis (the latter not shown in the picture). The bottom third shows the central vascular cylinder with the parenchyma, the phloem, the xylem and, the endodermis. In the functioning root, the gas spaces of the aerenchyma are inflated with air, rendering mechanical resistance and helping distribution of oxygen throughout the root. Image by Leite et al. 2017

Many plant tissues undertake PCD, a phenomenon that can be associated with modifications in cell walls (Tavares et al. 2015). In seeds, endosperms and cotyledons may undertake PCD after germination takes place. At the same time as cells die, their reserves (starch, lipid, and cell wall polysaccharides) are transferred to the growing seedling, allowing them to quickly cross the phase of establishment and become competitive with others (Buckeridge 2010). Fruit tissues may develop in the same way. While entering PCD, the middle lamella (the layer of polysaccharides between plant cells) is dissolved, providing means for seed dispersion. The flesh of the fruit becomes edible, and we use this as important food products. Thus, death-related processes may be adaptive because they “create” function.

Another process that is capable of creating a function in plants is the formation of the aerenchyma. Aerenchyma are a set of interconnected gas spaces that are thought to facilitate oxygen transport within the plant (see the video below). We now report in Annals of Botany (Leite et al. 2017) a complete analysis of cell wall-related events during aerenchyma formation in plants. We unveiled some of the complexity of the Glycomic Code of the cell walls (Buckeridge 2017), and showed that while PCD is completed, cell walls probably acquire another function. While one of the hemicelluloses is retrieved from the wall, others stay and seem to be modified to bind more strongly to cellulose. The result is the formation of a composite that coats the inner part of the gas channels. The latter is thought to be responsible for the conduction of air and delivering of oxygen to the living cells of the root, which absorb nutrients and transport them to the upper part of the plant.