Electrophoretic profiling and immunocytochemical detection of pectins and arabinogalactan proteins in olive pollen during germination and pollen tube growth

• Published in: Annals of botany 2013-08, Vol.112 (3), p.503-513
• Main Authors: Castro, Antonio J., Suárez, Cynthia, Zienkiewicz, Krzysztof, de Dios Alché, Juan, Zienkiewicz, Agnieszka, Rodríguez-García, Maria Isabel
• Format: Article
• Language: English
• Subjects: Antibodies; Cell walls; Cytoplasm; Electrophoresis - methods; Epitopes; Galactans - metabolism; Germination; Immunohistochemistry - methods; Microscopy, Electron, Transmission; Olea - metabolism; Olea - physiology; Olea - ultrastructure; Olives; Original; Pectins - metabolism; Plant cells; Pollen; Pollen Tube - growth & development; Pollen Tube - metabolism; Pollen Tube - ultrastructure; Pollen tubes; Somatic cells
• ISSN: 0305-7364; 1095-8290
• DOI: 10.1093/aob/mct118

• Background and Aims Cell wall pectins and arabinogalactan proteins (AGPs) are important for pollen tube growth. The aim of this work was to study the temporal and spatial dynamics of these compounds in olive pollen during germination. • Methods Immunoblot profiling analyses combined with confocal and transmission electron microscopy immunocytochemical detection techniques were carried out using four anti-pectin (JIM7, JIM5, LM5 and LM6) and two anti-AGP (JIM13 and JIM 14) monoclonal antibodies. • Key Results Pectin and AGP levels increased during olive pollen in vitro germination. (1 → 4)-β-D-Galactans localized in the cytoplasm of the vegetative cell, the pollen wall and the apertural intine. After the pollen tube emerged, galactans localized in the pollen tube wall, particularly at the tip, and formed a collar-like structure around the germinative aperture. (1 → 5)-α-L-Arabinans were mainly present in the pollen tube cell wall, forming characteristic ring-shaped deposits at regular intervals in the sub-apical zone. As expected, the pollen tube wall was rich in highly esterified pectic compounds at the apex, while the cell wall mainly contained de-esterified pectins in the shank. The wall of the generative cell was specifically labelled with arabinans, highly methyl-esterified homogalacturonans and JIM 13 epitopes. In addition, the extracellular material that coated the outer exine layer was rich in arabinans, de-esterified pectins and JIM13 epitopes. • Conclusions Pectins and AGPs are newly synthesized in the pollen tube during pollen germination. The synthesis and secretion of these compounds are temporally and spatially regulated. Galactans might provide mechanical stability to the pollen tube, reinforcing those regions that are particularly sensitive to tension stress (the pollen tubepollen grain joint site) and mechanical damage (the tip). Arabinans and AGPs might be important in recognition and adhesion phenomena of the pollen tube and the stylar transmitting cells, as well as the egg and sperm cells.