Salinity-driven changes in Salicornia cell wall nanomechanics and lignin composition

Abstract

Widespread increases in soil salinization significantly reduce agricultural lands. Nevertheless, salt-tolerant plants, such as Salicornia europaea L., can play a crucial role in the reclamation of these lands. We selected S. europaea for this study due to its potential to mitigate soil salinization and its numerous applications, such as intercropping in agriculture, biocompounds production and bioenergy. This work was designed to determine whether different salinities induce significant biophysical, anatomical, lignin and gene transcript changes in S. europaea. Through atomic force microscopy (AFM), we revealed that salinity stimulated an increase in cell wall elasticity (CWE) as an important physiological mechanism of adaptation known as cell’s turgor conservation effect. Direct values of the cell wall stiffness subjected to salinity were obtained, with Young’s modulus (E) ranging from low and high salinity 0.52 to 0.03 MPa. The softening of the cell wall properly correlated with an increase in cell size, plant cells under strong salinity 1000 mM NaCl, swelled 5.4 times. The best salinity range found for its optimum growth was 200–400 mM NaCl. At higher salinities, we identified increases in the lignified xylem, large calcium oxalate crystals, and in transcript amounts of SeSOS1 and SeNHX1, which has a significant negative correlation with cell wall stiffness (−0.57 and −0.95, respectively). The high syringyl and guaiacyl ratio (S/G) in lignin for 0–400 mM NaCl may have influenced the rigidity and hydrophobicity of the cell walls. A positive S/G ratio and sugar yields are associated with higher bioethanol production, these values may also be useful for agriculture, biorefinery, biocompounds and plant-breeding applications. We conclude that salinity indeed influenced the cell wall traits of S. europaea. This halophyte is capable of markedly softening its cell wall as a way of adapting to the high level of salinity. Our presented insights and correlations not only provide a better understanding of cell wall remodelling but are also considered vital traits of adaptation strategies that this halophyte holds under salinity environment. These inputs can also be applied in future research aiming to produce biomass and biofuel or to improve the salinity tolerance during the cultivation of non-tolerant plants, crops and glycophytes, which is a significant challenge in agriculture, particularly in arid and coastal regions. The unique properties of the S. europaea cell walls could also inspire the development of materials with enhanced nanomechanical elasticity for resistance to osmotic stress.