Identification of Proteins Present in the Douglas Fir Ovular Secretion: An Insight into Conifer Pollen Selection and Development

A week before fertilization in Douglas fir, a secretion fills the micropylar chamber of the ovule that houses the engulfed pollen. This liquid initiates pollen tube formation. This secretion is rich in proteins. Proteomic analysis using gel electrophoresis, combined with quadrupole time‐of‐flight tandem mass spectrometry peptide sequencing, identified nine of the more abundant proteins as a 90 kDa xylosidase with an isoelectric point (pI) of 6.6, a 65 kDa xylosidase with a pI of 6.0, a 70 kDa invertase with a pI of 6.3, a 50 kDa invertase with a pI of 6.5, a 45 kDa galactosidase with a pI of 7.8, a 29 kDa galactosidase with a pI of 5.9, a 40 kDa aspartyl protease with a pI of 5.5, a 37 kDa peroxidase with a pI of 7.9, and a 33 kDa serine carboxypeptidase–like protein with a pI of 4.5. This research presents the first evidence that conifer ovular secretion proteins may influence pollen selection and development.