Developmental stages of the secretory tissue and sugar composition of the pollination drop in the South American Ephedra triandra

Abstract

The pollination drop is a secretion produced by the female cones of many gymnosperms. Its primary function is linked to pollen capture and the subsequent transport of pollen into the ovule by contacting the nucellar surface, thus facilitating pollen germination. This contribution aims to achieve two objectives: (a) histologically analyze the female cones of Ephedra triandra to illustrate the tissue responsible for the secretion of the pollination drop at different developmental stages; (b) determine the concentration and sugar composition of this secretion and discuss the results in the context of E. triandra’s pollination systems within its genus. During ovule development, a starch accumulation occurs in the upper section of the nucellus after the formation of the pollen chamber. Subsequently, starch degradation coincides with the appearance of the pollination drop at the extreme end of the micropillar tube. The pollination drop exhibits a solute concentration of approximately 12 %, primarily composed of sugars (glucose and fructose). The pollination drops in E. triandra showedasolute concentration higher than wind-pollinated Gymnosperms (e.g., <5 %) and composed by sugars usually present in the nectar of Angiosperms, indicating that this species could also interact with animal pollinators to produce their seeds.