Traits allowing Avicennia marina propagules to overcome seawater salinity

The present study investigated the mechanism by which propagules of Avicennia marina overcome the high surrounding salinity and how they withstand and establish in such a stressful environment. Mature propagules were collected from mother trees at two sites along the Saudi Read Sea shoreline. Based on their sizes, they were divided into small, medium and large propagules. Their morphological characterization and sodium, potassium, chloride and total sugar concentrations (TSC) in embryonic axis, cotyledons and coat were assessed. Toxic ions (Na+ and Cl−) were mainly accumulated in the propagule coat by which they were trapped away from the embryo. The high total sugar accumulation in cotyledons might help in embryonic axis growth. The early development of the embryonic axis inside the propagule before dispersing from the mother plant might help in overcoming high salinity during germination stage and seedling establishment. The large propagules from 'Al Birk' site which exhibited the highest TSC and K+/Na+ ratio in cotyledons and well-developed embryonic axis appeared promising for mangrove restoration programs along the Red Sea Shorelines.