Soil salinity is a major abiotic stressor that constrains plant growth and development, yet the coordinated regulatory mechanisms underlying salt stress impacts on plant cell mechanical properties and the cytoskeleton remain elusive. In this study, tobacco suspension cells were employed as a model system. Combining mechanical measurements, fluorescence microscopy imaging, and bright-field morphological observation, we systematically characterized the dynamic response patterns of cell-generated surface stress (ΔS), cell viscoelastic index (CVI), microfilament cytoskeleton structure, as well as cell morphology and plasmolysis under NaCl stress ranging from 50 to 150 mmol/L. The results revealed three distinct response thresholds: 50 mmol/L NaCl treatment induced only transient ΔS fluctuations and mild plasmolysis, with no significant changes in CVI or microfilament fluorescence intensity, suggesting a safe tolerance threshold. The 75–100 mmol/L NaCl treatments triggered reversible “rise–recovery” mechanical responses in ΔS and CVI. The microfilament cytoskeleton showed minor structural adjustments, and plasmolysis increased gradually but remained reversible, defining this range as a reversible acclimation phase. The 125–150 mmol/L NaCl treatment caused an irreversible decline in ΔS (with a sharp instantaneous drop at 150 mmol/L). CVI variations diminished and stabilized after 6 h. The microfilament cytoskeleton suffered progressive disruption, as fluorescence intensity dropped to 1% of the control group at 150 mmol/L, accompanied by severe plasmolysis and protoplast shrinkage, indicating irreversible cellular damage. These findings demonstrate a concentration-dependent gradient effect of NaCl stress, highlighting tight coordination between mechanical properties, cytoskeletal integrity, and morphological adaptation. This work provides critical cytological insights into the molecular regulation of plant salt stress responses.
Zhou et al. (Mon,) studied this question.