Abstract
Meristematic activity response of Posidonia oceanica shoots was assessed along a gradient of sediment sulfate reduction rates (SRR) and sediment sulfide pools (SSP) to test if meristematic activity could be used as an early indicator of seagrass health. The percentage of nuclei in the G2 phase of the cell cycle was used as a proxy of the cell division rate and therefore of the meristematic activity. The variability observed in the percentage of dividing cells (i.e. those containing nuclei in the G2 phase) in P. oceanica meristems was closely (> 80% of total variance) coupled to variability in SSP and SRR. The percentage of nuclei in the G2 phase exponentially declined with increasing SSP and SRR, reaching the lowest values (< 5%) when plants were growing on sediments with SSP > 0.001 mol AVS (acid volatile sulfides) m(-2). These results strongly suggest that the meristematic activity can be used as an early warning indicator of seagrass stress.