A Comparative Analysis of the Relative Water Content of the Pollen of Early Diverging Angiosperms

The pollen of most angiosperms goes through a process of dehydration before anthesis, the opening of the flower (Heslop-Harrison 1979a). During dispersal, further dehydration often occurs (Heslop-Harrison 1979b). Dehydrated pollen comes in two degrees: hydrated (also termed desiccation-sensitive or recalcitrant) at greater than 30% water content by mass and dehydrated (also termed desiccation-tolerant or orthodox) at less than 30% water by mass (Franchi et al 2002, 2011). Most species tend to undergo some degree of dehydration, or developmental arrest, before anther opening (Franchi et al 2002). Angiosperms are known to have much faster reproductive processes than other seed plants, which may be in part due to a novel ability to germinate pollen rapidly. The degree to which mature pollen is hydrated is directly correlated to germination speed, and with little being known about the pollen germination process of early diverging angiosperm lineages other than their ability to rapidly do so, the degree of hydration of a species is of particular interest. As such, this study is meant to shed light on the hydration status of pollen within early divergent angiosperm lineages. Five early-diverging angiosperms were selected in order to encompass a wide range of ecological strategies. The pollen of the woody terrestrial Liriodendron tulipifera and the aquatic Nymphaea odorata were found to be dehydrated, whereas that of the woody semi-aquatic Hedyosmum brasiliense and the herbaceous aquatics Nuphar advena and Brasenia shreberi were found to have hydrated pollen. These data reveal a remarkable diversity of pollen strategies among ancient angiosperms.

Andrew Moffatt's Honors Thesis, May 7th, 2012