Lignin synthesis plays an essential role in the adaptation of Haloxylon ammodendron to adverse environments

Haloxylon ammodendron is a desert shrub exhibiting remarkable tolerance to adverse environments, making it an excellent model for studying the mechanisms by which plants adapt to harsh environmental conditions. Lignin, a crucial component of plants, has been shown to play an important role in the adaptation of H. ammodendron to osmotic and salt stress. Therefore, this study was focused on the role of lignin synthesis by H. ammodendron in its adaptation to osmotic and salt stress (imposed by 0.4 % sorbitol and 350 mM NaCl, respectively). We investigated lignin deposition, the polymerization of lignin monomers, water content and adjustment of osmotic potential in assimilating branches of H. ammodendron, as well as gene expression and small molecules related to lignin biosynthesis. The results indicated that osmotic and salt stress induced the activity of peroxidase (POD) and laccase (LAC), while H₂O₂ concentration also increased. The genes encoding functions associated with lignin biosynthesis in both shoots and roots were upregulated and lignin accumulation in H. ammodendron increased, thereby maintaining osmotic potential and shoot water content under stress. These results showed that osmotic and salt stresses significantly increased lignin production in H. ammodendron, polymerization of lignin monomers, and the expression of genes encoding functions correlated to lignin synthesis. In addition, under osmotic stress, phenylalanine and p-coumaric acid increased in the shoots and roots, as did coniferyl alcohol and sinapyl alcohol. Overall, this study confirmed the role of lignin biosynthesis in the stress resistance of H. ammodendron, providing further insights into its adaptive strategies to adversity, and suggesting new ideas for improving the resistance of cultivated plants.