Metabolic Adjustment of Arabidopsis Root Suspension Cells during Adaptation to Salt Stress and Mitotic Stress Memory.

Sessile plants reprogram their metabolic and developmental processes during adaptation to prolonged environmental stresses. To understand the molecular mechanisms underlying adaptation of plant cells to saline stress, we established callus suspension cell cultures from Arabidopsis roots adapted to high salt for an extended period of time. Adapted cells exhibit enhanced salt tolerance compared to control cells. Moreover, acquired salt tolerance is maintained even after the stress is relieved, indicating the existence of a memory of acquired salt tolerance during mitotic cell divisions, known as mitotic stress memory. Metabolite profiling using 1H NMR spectroscopy revealed metabolic discrimination between control, salt-adapted, and stress-memory cells. Compared to control cells salt adapted cells accumulated higher levels of sugars, amino acids, and intermediary metabolites in the shikimate pathway, such as coniferin. Moreover, adapted cells acquired thicker cell walls with higher lignin contents, suggesting the importance of adjustments of physical properties during adaptation to elevated saline conditions. When stress-memory cells were reverted to normal growth conditions, the levels of metabolites again readjusted. Whereas most of the metabolic changes reverted to levels intermediate between salt adapted and control cells, the amounts of sugars, alanine, GABA, and acetate further increased in stress-memorized cells, supporting a view of their roles in mitotic stress memory. Our results provide insights into the metabolic adjustment of plant root cells during adaptation to saline conditions as well as pointing to the function the mitotic memory in acquired salt tolerance.