Summary.The distribution of acetylated tubulin in microtubule arrays of conifer ceils was investigated by immunofluorescence techniques with 6-11B-l, a monoclonal antibody specific for posttranslationally acetylated c~-tubulins. In methacrylate sections of Pinus radiata and Pinus contorta root tip cells, acetylated tubulin was detected in mitotic spindles, phragmoplasts, and cortical microtubules. Furthermore, staining of isolated, intact cells of P. radiata and P. contorta indicated that all microtubule structures, including preprophase bands, prophase, metaphase and anaphase spindles, and phragmoplasts, contained some acetylated tubulin, and that the intensity of staining with 6-11B-1 was variable. For example, preprophase bands were lightly labelled, kinetochore fibres of anaphase spindles and phragmoplasts were heavily stained, and metaphase spindles had a granular appearance suggesting discontinuous acetylation of their constituent microtubules. This first report of the presence of acetylated tubulin in conifer cells is in contrast to our results with two species of angiosperms where no acetylated tubulin was detected. The significance of this and the variability of the intensity of staining in conifer arrays is discussed in terms of microtubule dynamics.

The distribution of tyrosinated and detyrosinated tubulin in microtubuIe arrays of pine and onion ceils was investigated by immunoftuorescence techniques. Staining of isolated ceils and methacrylate sections of Pinus radiata and Allium cepa root tips indicated that all microtubule structures contained tyrosinated tubulin but not the posttranslationally modified detyrosinated tubulin. The detyrosinated tubulin epitope was, however, created in vitro by treating both sections and fixed whole ceils with carboxypeptidase A.

Methacrylate embedding followed by resin removal has been used for the first time to visualize a membrane-associated antigen at the tissue level. Monoclonal antibody JIM 84 was used to stain the Golgi apparatus of gymnosperm (conifer) embryos by light microscope immunocytochemistry. Specificity of labelling was confirmed by electron microscope immunocytochemistry using LR-white resin. GA staining was evident in all stages of white spruce somatic embryo development from immature to mature. Some regions of the somatic embryos (e.g. root cap/suspensor region) stained more vigorously than other regions (hypocotyl/cotyledon end). GA also stained in roots of Monterey pine and Douglas fir. Unlike the situation in most angiosperms, JIM 84 antigen appears to be absent from the conifer plasma membrane. However, it appears to be present in representatives of both major classes of higher plants.