CONIFER SOMATIC EMBRYOGENESIS FOR STUDIES OF PLANT-CELL BIOLOGY

Embryogenic cultures have been produced for a wide range of conifers a nd current methods developed for spruce permit the maturation of high quality embryos that can be desiccated and then germinated to form pla ntlets. Embryogenic suspensions consisting of immature embryos are an excellent source of regenerable protoplasts. This review considers exa mples of applications of embryogenic suspension cultures for basic stu dies in three areas of plant cell biology, a) Immunofluorescence studi es of microtubules in mitotic spruce cells reveal focused spindle pole s at prophase and anaphase, suggesting the presence of microtubule org anizing centers (MTOCs). Antibodies known to recognize animal MTOCs do not stain the polar regions but do stain developing kinetochores. b) Embryo-derived protoplasts regenerate directly to somatic embryos. Flu orescence studies of the cytoskeleton in freshly derived protoplasts r eveal random cortical microtubules and a fine network of actin filamen ts. During culture, protoplasts change shape and develop transverse co rtical microtubule arrays. Embryonal cells of newly formed embryos pos sess distinctive arrays of cortical microtubules and networks of fine actin filaments while suspensor cells are characterized by transverse cortical microtubules and longitudinal actin cables. c) Transmission e lectron microscope studies of endocytosis in spruce protoplasts reveal an endocytotic pathway similar to that described previously for soybe an. Uptake results are confirmed using high pressure freeze fixation i nstead of conventional chemical fixation.