Root cortex: structural and functional variability and responses to environmental stress

The cortex is the basic part of the primary root body and represents an important constituent of the root, both structurally and functionally. In monocotyledons, it might persist during the entire life of the root. In dicotyledons, with limited secondary thickening it might persist for a long time and be subject to dilatation growth. In intensively secondary-thickening roots, the cortex gradually deteriorates and is replaced by secondary tissues-the periderm. The functions of cortical tissues are diverse. The endodermis, and to some extent the exodermis, represent apoplastic barriers that control the uptake and radial transport of water and solutes by the root. However, these layers have several additional functions such as mechanically protecting the stele and protection against pathogens and parasites. Although the mid-cortex (or mesodermis) is primarily the site for reserve material deposition, it can also have several different functions that depend on the species and growth conditions. These include aeration in hypoxia (aerenchyma formation), and the location for symbiosis and even photosynthesis. The cortex varies widely amongst species and even in various root types of the same species. It might be designated as a root buffer zone, especially under stress conditions. Some aspects of the development, structure and function of cortical tissues are discussed in this report.