Reproduction in seagrasses: pollination in Amphibolis antarctica

• Published in: Proceedings of the Royal Society of London. Series B. Biological Sciences
• Format: Article in Journal/Newspaper
• Language: English
• Published: The Royal Society 1983
• Subjects: Antarc*; Antarctica
• Online Access: http://dx.doi.org/10.1098/rspb.1983.0064; https://royalsocietypublishing.org/doi/pdf/10.1098/rspb.1983.0064

Pollination in the dioecious marine angiosperm Amphibolis antarctica has been studied in plants maintained in constant conditions. When the ripe filiform pollen is applied to the submerged stigmas, the grains adhere tenaciously to the receptive zones of the branches. Microsopical examination of the stigmas at this stage shows that a meniscus is developed at each point of pollen-stigma contact and that in every case this results from local coalescence of a proteinaceous substance coating the grain wall and a film of secretion product on the surface of the stigma. Once the grains are attached to the stigma, pollen germination begins. At the site of the future germinal aperture a small region of the pollen wall fabric is gelatinized, presumably by glycosidase activity. At the same time as this process, or shortly afterwards, a lens of polysaccharide is deposited beneath the incipient aperture. The lens hydrates and extrudes, pushing the lax region of wall outwards to form a surface papilla. Extension is limited and the apertural perforation originates when the degraded wall fabric in the distal region of the papilla finally disperses. The pollen tube then emerges through the aperture and rapidly grows towards the stigma, the tube tip eventually making contact with the secretion layer. Entry of the tube into the stigma requires enzymic erosion of the stigma cuticle, and esterases contained in the stigma secretion are probably implicated in the process, but penetration was not directly observed. None the less, cuticle lysis must occur because some hours after pollen attachment pollen tubes are seen in the epidermal tissue of the stigma branch and growing towards the ovary. The principal features of the seagrass pollination system are compared with their counterparts in the pollination system of the land-based flowering plants, and the comparisons reveal marked similarities as well as differences between them.