Figure 9.

Simplified Scheme Depicting the Regulation of Cell Cycle Inhibition and Cell Differentiation in Response to Osmotic Stress.

Very rapidly (within hours) after stress imposition, ethylene (C₂H₄) production is triggered, inhibiting CDKA activity through a posttranscriptional mechanism that reversibly inhibits the cell cycle by G1/S and G2/M arrest. Cell cycle arrest is independent of EIN3 transcriptional control and possibly mediated by a MAPK signaling pathway or the ribonuclease EIN5. In a later phase, a different signal leads to permanent inhibition and exit from the mitotic cell cycle in favor of the endocycle and cell differentiation. Later in leaf development, meristemoid division activity becomes higher in stressed leaves and the enhanced meristemoid division results in a small increase in cell numbers.