Biochemical and Immunocytological Characterizations of Arabidopsis Pollen Tube Cell Wall    

Abstract

During plant sexual reproduction, pollen germination and tube growth require development under tight spatial and temporal control for the proper delivery of the sperm cells to the ovules. Pollen tubes are fast growing tip-polarized cells able to perceive multiple guiding signals emitted by the female organ. Adhesion of pollen tubes via cell wall molecules may be part of the battery of signals. In order to study these processes, we investigated the cell wall characteristics of in vitro-grown Arabidopsis (Arabidopsis thaliana) pollen tubes using a combination of immunocytochemical and biochemical techniques. Results showed a well-defined localization of cell wall epitopes. Low esterified homogalacturonan epitopes were found mostly in the pollen tube wall back from the tip. Xyloglucan and arabinan from rhamnogalacturonan I epitopes were detected along the entire tube within the two wall layers and the outer wall layer, respectively. In contrast, highly esterified homogalacturonan and arabinogalactan protein epitopes were found associated predominantly with the tip region. Chemical analysis of the pollen tube cell wall revealed an important content of arabinosyl residues (43%) originating mostly from (1/5)-a-L-arabinan, the side chains of rhamnogalacturonan I. Finally, matrix-assisted laser desorption ionization time-of-flight mass spectrometry analysis of endo-glucanase-sensitive xyloglucan showed mass spectra with two dominant oligosaccharides (XLXG/XXLG and XXFG), both being mono O-acetylated, and accounting for over 68% of the total ion signals. These findings demonstrate that the Arabidopsis pollen tube wall has its own characteristics compared with other cell types in the Arabidopsis sporophyte. These structural features are discussed in terms of pollen tube cell wall biosynthesis and growth dynamics.

PECTIN METHYLESTERASE48 Is Involved in Arabidopsis Pollen Grain Germination

“…Immunolabeling of HG on Arabidopsis pollen tubes showed a dominant localization of the highly methylesterified HG in the tip and of partially methylesterified HG behind the tip region (Dardelle et al, 2010;Chebli et al, 2012). This labeling pattern is also observed in pollen tubes from plants possessing a solid style, such as species in the Solanaceae (potato [Solanum tuberosum], tobacco, and petunia [Petunia hybrida]), the Oleaceae (jasmine [Jasmium spp.…”

“…Immunolocalization was performed by cell surface labeling as described previously by Dardelle et al (2010) or on semithin sections. For the cell surface immunolabeling, pollen grains or pollen tubes in GM were mixed (v/v) with a fixation medium containing 100 mM PIPES buffer, pH 6.9, 4 mM MgSO 4 •7H 2 O, 4 mM EGTA, 10% (w/v) Suc, and 5% (w/v) formaldehyde and incubated for 90 min at room temperature.…”

“…Moreover, callose is also deposited periodically within the pollen tube to form plugs that maintain the tube cell in the expanding apical region. The outer cell wall in the tip and back from the tip is mostly composed of pectins, xyloglucan, cellulose, and proteoglycans such as arabinogalactan proteins (Geitmann and Steer, 2006;Dardelle et al, 2010;Chebli et al, 2012;Nguema-Ona et al, 2012).…”

“…The pollen tube cell wall of many species, including tobacco (Nicotiana tabacum; Li et al, 1995;Ferguson et al, 1998), lily (Lilium longiflorum; Roy et al, 1997), and Arabidopsis (Arabidopsis thaliana; Lennon and Lord, 2000;Dardelle et al, 2010), is characterized by one layer in the tip region and two distinguishable layers back in the shank. Back from the tip, the inner layer is mainly composed of callose, a (1,3)-b-glucan, which is not detectable in the tip region in normal growth conditions (Ferguson et al, 1998;Derksen et al, 2002;Parre and Geitmann, 2005b;Dardelle et al, 2010;Chebli et al, 2012). Moreover, callose is also deposited periodically within the pollen tube to form plugs that maintain the tube cell in the expanding apical region.…”

“…Pectins are complex polysaccharides consisting of homogalacturonan (HG), rhamnogalacturonan I, rhamnogalacturonan II, and xylogalacturonan (Vincken et al, 2003;Dardelle et al, 2010;Fry, 2011;Dumont et al, 2014). HG is a polymer consisting of repeating units of (1,4)-a-D-galacturonic acid (GalUA) that is synthesized in the Golgi apparatus and may be deposited in the cell wall in a highly methylesterified form (Zhang and Staehelin, 1992).…”