The obturator bridges the downward transit of the pollen tube through style to ovary in many angiosperms. Examining pollen tube growth kinetics in the pistil in Malus × domestica and relating these to changes occurring on the obturator using histochemistry and immunocytochemistry in order to determine how the key access point of the obturator is mediated, Losada and Herrero show that glycoprotein secretion is required for a lightning pollen tube wall elongation on the surface of the obturator.
This secretion is depleted following on from the passage of pollen tubes, which strongly suggests that glycoprotein secretion has a pivotal role in regulating pollen tube access to the ovule. The glycoproteins involved are present also in the apple stigma, which has the same developmental origin and points to a conserved evolutionary trend among flowering plants.
Losada, J. M., & Herrero, M. (2017). Pollen tube access to the ovule is mediated by glycoprotein secretion on the obturator of apple (Malus × domestica, Borkh). Annals of Botany, mcw276. https://doi.org/10.1093/aob/mcw276