Changes to Cortical Cell Traits of Maize Growing Through a Compacted Layer

Soil compaction has a major impact on root development and consequently plant yields due to influences on root architecture, morphology and anatomy. The most common morphological change associated with roots growing through strong soils is root thickening with roots having been observed to radially expand under higher levels of impedance. Precise details about what happens to the cellular structure of the root tissues remains largely unknown, while cellular anatomy will form the basis for this morphological response to a localised stress such as impedance. We studied the cellular changes of four genotypes of maize that show variable amounts of thickening upon entering a denser soil layer, including how these traits changed along the root axis. To quantify the internal structures of roots, and their ability to grow through a compacted layer, X-ray Computed Tomography was used to highlight sections along the root axis of interest. Four points along the root axis were selected (top of the root system, before entering compaction, within compaction and beyond the compaction zone) and roots were sectioned with a vibrating microtome prior to imaging. Both cortical and stele area react to compaction, expanding radially. It will be demonstrated that root cortical traits respond to compaction and that genotypes respond differently. Traits, such as cell area, will change along the root axis when it grows through a locally applied stress of a denser soil layer. Cell areas within 3 cortical zones were measured before, within and after compaction and show anatomical responses accordingly. These changes may be correlated with the ability to overcome compaction and penetrate through a harder layer.

Fig: Three cross sections of maize roots along a root axis growing through a compacted layer, illustrating the change in anatomical traits from left to right: before entering compaction, within compaction and beyond the compacted layer. Roots radially expand by expanding their stele and cortical areas and cell area changes can be linked to the cortical expansion. Images obtained by vibrating microtome sectioning and laser scanning confocal microscopy. Scale: 250 µm.