Analysis of the female reproductive secretions of Cycas revoluta
Date
2019
Authors
Morrison, Nora S.
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Abstract
Gymnosperms produce sexual fluids for reproduction. Cycads ovules produce both pollination drops and a fluid from their megagametophytes. The latter pools in the archegonial chamber and mediates fertilization. Megagametophyte fluid from Cycas revoluta was analyzed by various techniques and, where suitable, was compared to the pollination drop of Taxus x media, yew, a commonly analyzed gymnosperm ovule secretion. Osmolarity was found to be 672 ± 66 mOsm from four individual plants, which was similar to the osmolarity of yew pollination drops. Of the 661 proteins revealed by mass spectrometry using an Orbitrap Fusion, 372 were of plant origin, and 220 were of bacterial origin. These results differ from yew in that the proteins in Cycas are almost entirely degradome, as opposed to Taxus in which are almost entirely secretome. The presence of bacteria in cycads suggests that the reproductive system of Cycas revoluta is not a closed system. In Cycas revoluta, the fluid that causes pollen tubes to burst and provides a medium in which sperm can swim has solutes that are released by the megagametophyte, indicating that the female controls major events prior and during fertilization.