Pollination and Growth of Pollen Tubes in Common Juniper (Juniperus communis L.: Cupressaceae Rich. ex Bartl.)

Pollination and fertilization are crucial stages in sexual reproduction of coniferous plants.The period of high concentrations of airborne juniper pollen in the pollination season lasts no more than 4-6 hours within one calendar day.This event occurs in precisely the same way every year regardless of weather conditions in the reception period and specific growth conditions of the juniper.The study addresses the influence of external agents on dynamics of exudation of a juniper pollination droplet.The duration of exudation and the volume of secretory liquid exuded by tissues of ovules are determined by the presence of external agents on the surface of the pollination droplet, their sizes, and their physical and chemical properties.The chemical composition of the pollination droplet has been studied.About 40 substances belonging to different classes of organic compounds have been identified in the volatile fractions of the pollination droplet.Sugars of the juniper pollination droplet are only represented by two monosaccharides: glucose and galactose.The major amino acids are arginine, aspartic and glutamic acids.Results of the study confirm the complex chemical composition and multi-functionality of the juniper pollination droplet.The pollination mechanism of the juniper is effective and selective.Pollination failure leads to degradation and necrosis of tissues of ovules and macrostrobili.The morphological structure of pollen grains of the juniper predetermines processes of pollen germination at early stages.The hydrophilic capsule formed after pollen hydration facilitates exine rupture and shedding.This capsule is retained until fertilization occurs.The distal tip of the pollen tube stays in the capsule throughout its growth period.In the in vitro culture, pollen tubes of the juniper develop non-uniformly.To assess juniper pollen viability, it is necessary to take into account the stage of development of pollen tubes.