The viscoelastic properties of Nicotiana tabacum BY-2 suspension cell lines adapted to high osmolarity.

To survive and grow, plant cells must regulate the properties of their cellular microenvironment in response to ever changing external factors. How the biomechanical balance across the cell's internal structures is established and maintained during environmental variations remains a nurturing question. To provide insight into this issue we used two micro-mechanical imaging techniques, namely Brillouin light scattering and BODIPY-based molecular rotors Fluorescence Lifetime Imaging, to study Nicotiana tabacum suspension BY-2 cells long-term adapted to high concentrations of NaCl and mannitol. The molecular crowding in cytoplasm and vacuoles was examined, as well as tension in plasma membrane. To understand how sudden changes in osmolarity affect cellular mechanics, the response of the control and the already adapted cells to further short-term osmotic stimulus was also examined. The viscoelasticity of protoplasts is altered differently during adaptation processes compared to responses to sudden hyperosmolarity stress. The applied correlative approach provides evidence that adaptation to hyperosmotic stress leads to different ratios of protoplast and environmental qualities that help to maintain cell integrity. The viscoelastic properties of protoplasts are an element of plant cells long-term adaptation to high osmolarity. Moreover, such adaptation has an impact on the response to the hyperosmolarity stress.