WILLIAMS, GEOFFREY L.* AND KAREN L. KLOMPARENS. Center for Electron Optics and Department of Botany and Plant Pathology, Michigan State University, MI 48824. - Reconstructing the ovuliferous scale in Picea pungens to examine the mechanisms surrounding pollination drop secretion.
Three-dimensional reconstruction is a powerful tool for examination of
morphology and developmental events. This study takes advantage of
three-dimensional reconstruction using a laser scanning microscope
(LSM) to elucidate the events surrounding the pollination drop in
spruce. Picea pungens was selected for this study because of
the unique pollination system and because it grows well in
mid-Michigan. The ovuliferous scale is the structure the bears the
seed pair on the cone and is where the pollination drop originates.
Because the ovuliferous scales are thick and relatively optically
opaque, they were embedded in wax and serially sectioned to take
advantage of digital image collection with a LSM. Data were collected
to reconstruct in three dimensions the serial images using a Silicon
Graphics, Inc. workstation (SGI), illustrating the whole structure
from the inside out and back in again. The SGI was also used to
produce 3D images in various views that are not possible or convenient
in conventional reconstruction. By looking at samples collected over
time, it is possible to trace the development of the ovule and the
surrounding structures, especially the development of tracheids at the
chalazal end of the integument. The sequence of developing scales
collected from the same trees contributes to the elucidation the
pollination drop mechanism.
Key words: 3D-reconstruction, LSM, ovuliferous scale, Picea, pollination