Dr Elizabeth Sinclair & Angela Rossen
UNIVERSITY OF WESTERN AUSTRALIA
Many of us know when pollen is in the air – its allergy season. But have you ever thought about what happens underwater? What do the marine flowering plants do with their pollen? Put your head under water in the middle of winter and have a look!
The cooling water temperatures in the southern hemisphere trigger mass flowering events in the Posidonia meadows. The flowering stems of the ribbon weed Posidonia australis – a long-lived, slow growing seagrass endemic to temperate Australian coastal waters – proudly displays its flowers with bright red anthers (Fig. 1 and 2) in or above the leaf canopy. The flowers are monoecious, containing both male (anthers) and female (stigma) parts. The opportunity for self pollination is reduced by having anthers release pollen before the stigmas become receptive.
Flowering stems were collected during a field trip to Rottnest Island, Western Australia. They were brought back to the laboratory for photographing. The flowers were kept in the fridge, but continued to mature and released their pollen. This video captures the exact moment of pollen release – something that has never been seen before. Elongated sticky pollen capsules are violently catapulted into the water, free of the leaves. The odds of a pollen grain actually coming into contact with a receptive stigma from another plant seem very low. However, it happens often enough, in fact every time a new seed is produced.
This video captures the pollen release from the anthers.
Seagrass pollen is highly modified for moving around in the water. The pollen grains are small, elongated and very difficult to see with the naked eye. They are close to invisible in the water column. The use of genetic markers to identify paternity of seeds (pollen donor plant) demonstrates pollen is mixing well and capable of moving 10’s to 100’s of metres (Sinclair et al. 2014). Seed production is extremely prolific in the seagrass meadows within the Perth metropolitan waters, but highly variable among meadows across Australia.
Fig 1. Flowers of Posidonia australis (Photo Angela Rossen)
Fig 2. Immature anthers of of Posidonia australis
(Photo Angela Rossen)
Reference
Sinclair EA, Gecan I, Krauss SL, Kendrick GA (2014) Against the odds: complete outcrossing in a monoecious clonal seagrass Posidonia australis (Posidoniaceae). Annals of Botany, 113, 1185–1196.