Cell Cycle Modulation in the Response of the Primary Root of Arabidopsis to Salt Stress

Abstract

Salt stress inhibits plant growth and development. We investigated the importance of cell cycle regulation in mediating the primary root growth response of Arabidopsis to salt stress. When seedlings were transferred to media with increasing concentrations of NaCl, root growth rate was progressively reduced. At day 3 after transfer of seedlings to growth medium containing 0.5% NaCl the primary roots grew at a constant rate well below that prior to the transfer, whereas those transferred to control medium kept accelerating. Kinematic analysis revealed that the growth reduction of the stressed roots was due to a decrease in cell production and a smaller mature cell length. Surprisingly, average cell cycle duration was not affected. Hence, the reduced cell production was due to a smaller number of dividing cells, i.e. a meristem size reduction. To analyze the mechanism of meristem size adaptation prior to day 3, we investigated the short-term cell cycle events following transfer to saline medium. Directly after transfer cyclin-dependent kinase (CDK) activity and CYCB1;2 promoter activity were transiently reduced. Because protein levels of both CDKA;1 and CDKB1;1 were not affected, the temporary inhibition of mitotic activity that allows adaptation to the stress condition is most likely mediated by posttranslational control of CDK activity. Thus, the adaptation to salt stress involves two phases: first, a rapid transient inhibition of the cell cycle that results in fewer cells remaining in the meristem. When the meristem reaches the appropriate size for the given conditions, cell cycle duration returns to its default.

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Salt Stress Signaling and Mechanisms of Plant Salt Tolerance

“…Salinity arrests the cell cycle transiently by reducing the expression and activity of cyclins and cyclin-dependent kinases that results in fewer cells in the meristem, thus limiting growth (10). In Arabidopsis, the reduction in root meristem size and root growth during salt stress is correlated with the downregulation of CDC2a (cyclin-dependent kinase), CycA2;1 and CycB1;1 (mitotic cyclins) (11).…”

“…In Arabidopsis, the reduction in root meristem size and root growth during salt stress is correlated with the downregulation of CDC2a (cyclin-dependent kinase), CycA2;1 and CycB1;1 (mitotic cyclins) (11). The activity of cyclin-dependent kinase is diminished also by post-translational inhibition during salt stress (10). Salt stress-induced abscisic acid (ABA) may also mediate cell cycle regulation.…”