HIGH-PRESSURE FREEZING IMPROVES THE ULTRASTRUCTURAL PRESERVATION OF IN-VIVO GROWN LILY POLLEN TUBES

We have used high-pressure freezing followed by freeze substitution (H PF/FS) to preserve in vivo grown lily pollen tubes isolated from the s tyle. The results indicated that HPF/FS (i)allows excellent preservati on of the pollen tubes, (ii) maintains in situ the stylar matrix secre ted by the transmitting tract cells, and (iii) preserves the interacti ons that exist between pollen tubes. Particular attention has been giv en to the structure of the pollen tube cell wall and the zone of adhes ion. The cell wall is composed of an outer fibrillar layer and an inne r layer of material similar in texture and nature to the stylar matrix and that is not callose. The stylar matrix labels strongly for arabin ogalactan proteins (AGPs) recognized by monoclonal antibody JIM13. The zone of adhesion between pollen tubes contains distinct matrix compon ents that are nor recognized by JIM13, and apparent cross-links betwee n the two cell walls. This study indicates that HPF/FS can be used suc cessfully to preserve in vivo grown pollen tubes for ultrastructural i nvestigations as well as characterization of the interactions between pollen tubes and the stylar matrix.