Cytological and Proteomic Analysis of Ginkgo biloba Pollen Intine

Abstract

The pollen intine plays important roles in pollen germination and tube growth, but related information in Ginkgo biloba remains unclear. We isolated and obtained de-exined pollen from G. biloba. Using fluorescent probes, we observed the strongest cellulose fluorescence in the pollen intine. De-esterified pectin immunolabeled with JIM5 was present throughout the entire cell wall, whereas esterified pectin recognized by the monoclonal antibody JIM7 was concentrated in some regions. Callose staining with aniline blue was observed across the entire surface of the pollen intine. These results were confirmed by Fourier Transform InfraRed (FTIR) analysis. We also used proteomic approaches to identify different proteins between mature and de-exined pollen (48 h after hydration) in vitro. Based on mass spectrometry, de-exined pollen had more proteins than mature pollen, including calmodulin, serine hydroxymethyltransferase, β-galactosidase 6, and class IV chitinase. According to Gene Ontology (GO) analysis, the differentially expressed proteins were mainly associated with transportation, defense reaction, sugar metabolism, energy metabolism, signal transduction, and cell wall formation. These findings suggest that most proteins involved in pollen germination and pollen tube growth are synthesized during pollen hydration, indicating the important role of pollen hydration in the reproductive process of G. Biloba.