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Seven isoforms of 85 kDa polypeptides (p85) were identified as methionine synthase (MetE) homologs by partial aminoacid sequencing in tobacco pollen tube extracts. Immunocytochemistry data showed a localization of the antigen on the surface of tip-focussed post-Golgi secretory vesicles (SVs), that appear to be partially associated with microtubules (Mts). The chemical dissection of pollen tube high speed supernatant (HSS) showed that two distinct pools of MetE are present in pollen tubes, one being the more acidic isoforms sedimenting at 15S and the remaining at 4S after zonal centrifugation through a sucrose density gradient. The identification of the MetE within the pollen tube and its possible participation as methyl donor in a wide range of metabolic reactions, makes it a good subject for studies on pollen tube growth regulation.

gaMS-2 is a gametophytic male-sterile mutant of maize, with sterile pollen grains developmentally blocked at the binucleate stage. To characterise differentially expressed proteins in gaMS-2 pollen, we compared protein profiles of anthers and mature pollen from heterozygous GaMS-2/gaMS-2 plants and wild type (wt) plants by two-dimensional electrophoresis (2-DE). A basic protein present at a greatly reduced level in GaMS-2/gaMS-2 anthers was subsequently identified by tandem mass spectrometry as Zea m 1 (a glycoprotein of 31 kDa), the major group-1 allergen of maize pollen and a member of the β-expansin 1 family. Moreover, we show that Zea m 1 can be deglycosylated by peptide N-glycosidase F. After deglycosylation, four major isoforms—Zea m 1a (more acetic), Zea m 1b, Zea m1c and Zea m 1d (more basic)—can be discriminated in wt anther in 2-DE immunoblots probed with a monoclonal antibody against the group-1 pollen allergen, whereas all the isoforms, especially Zea m 1a, exist at reduced levels in GaMS-2/gaMS-2 anthers. Furthermore, the reduced Zea m 1 accumulation in the mutant appears to occur in immature pollen but not in anther sporophytic tissues. Finally, we separated sterile pollen grains (at the mononucleate stage) from fertile ones using 42% Percoll solution, and found that Zea m 1 is barely detectable in sterile pollen grains. Together, our results indicate that a reduced Zea m 1 level is associated with the sterile phenotype of gaMS-2. [ABSTRACT FROM AUTHOR]