Pioneer root xylem development in Populus

Effective programmed xylogenesis is critical to the structural framework of the plant root system and its central role in the acquisition and long-distance transport of water and nutrients. Bagniewska-Zadworna et al. study the differentiation of tracheary elements (TEs) in pioneer roots of Populus trichocarpa grown in rhizotrons and find that the primary event is a burst of NO in thin-walled cells, followed by H₂O₂ synthesis and TUNEL-positive nuclei appearance. Subsequent events involve secondary cell wall formation and autophagy. Potential gene markers from the cinnamyl alcohol dehydrogenase (CAD) gene family that are related with secondary wall synthesis are associated with primary xylogenesis, showing clear expression in cells that undergo differentiation into TEs. The CAD genes appear to be involved in primary xylem differentiation and the formation of the cell walls in TEs before their functional maturity.