Seagrass hypocotyl hair development: the role of fresh water in the marine environment

Hypocotyl hairs, single celled structures that develop soon after seed germination, provide anchorage to sediments, initiate geotropism and may facilitate water uptake. The ability of germinating seedlings of marine... [ view full abstract ]

Hypocotyl hairs, single celled structures that develop soon after seed germination, provide anchorage to sediments, initiate geotropism and may facilitate water uptake. The ability of germinating seedlings of marine angiosperms to produce these structures may significantly influence their ability to maintain populations within estuarine environments. Such physiological adaptations that allow for greater attachment to the substrate by germinating seedlings would provide a competitive advantage. The development of hypocotyl hairs on germinants of the intertidal seagrass Zostera muelleri Irmisch ex Asch. was examined under differing temperature, salinity and light regimes. Hypocotyl hairs developed across the majority of the convex surface of the hypocotyls and was significantly influenced by both temperature (F2, 33 =12.06, p=0.002) and salinity (F5, 30 =28.21, p=<0.001). Seeds which germinated at 20°C in 24-h darkness had significantly more germinants developing hypocotyl hairs than all other treatments. Although the development of hypocotyl hairs was generally greater under higher salinity concentrations, germinants stored under lower salinity conditions had a greater likelihood of developing fully extended hypocotyl hairs, with greater extent than those stored at higher salinity concentrations. Considering that the requirements for ideal germination and hypocotyl hair development in Z. muelleri are somewhat constrained, the control of freshwater inputs may have a direct influence on the ability of Z. muelleri germinants to develop these structures which may ultimately influence their capacity to disperse. As such, the relationships between the physico-chemistry of the water column and hypocotyl hair development should be considered in the management of this ecologically important species.