Propagation of Ornamental Plants
4(1): 3-18, 2004
STATE OF DEVELOPMENT OF TECHNOLOGY FOR HAPLOID PRODUCTION FROM GYMNOSPERM MICROGAMETOPHYTE AND MEGAGAMETOPHYTE CULTURE
University of Lyon 1, UMR 5557 Microbial Ecology - Lwoff build., 69622 Villeurbanne cedex, France, Tel.: (33) 4 72 44 84 09, Fax: (33) 4 72 44 83 03, e-mail: Rene.Rohr@univ-lyon1.fr
This review summarizes the attempts made over the past few decades to cultivate the male and female gametophytes of gymnosperms in vitro and the results obtained either in order to follow the full ontogeny of the microgametophyte, or to regenerate whole haploid plants through androgenesis and gynogenesis.
In vitro spermatogenesis was achieved for a few species, including Taxus baccata and T. brevifolia. In vitro deviations from normal in vivo pollen ontogeny were reported for several species. These included the production of callus (Taxus) and undifferentiated tissues (e.g. Ephedra), development of tissues with either meristematic centers (Ginkgo, Ceratozamia), embryo-like structures (Ginkgo), and/or root differentiation (Picea abies). No organs developed into viable plantlets when they originated from male tissues.
Megagametophytes also may deviate in vitro from their normal course of ontogeny in three ways, which include callus and tissue formation, organogenesis or embryogenesis. The production of callus and subculturable tissue occured frequently, even from aged endosperm excised a long time after fertilization (e.g. several cycads and Ginkgo). Proembryos were formed on four-year old female gemetophyte tissue of Norway spruce. Early stages of direct embryogenesis was reported from Ginkgo haploid protoplasts of female origin. The most advanced stages of apogamy were achieved from the conifer female gametophyte in two different ways. Plantlets of Sequoia sempervirens have been regenerated through organogenesis from megagametophyte callus. Gametophyte embryogenesis only succeeded from endosperm culture of two Larix species and their reciprocal hybrid. Embryogenic development appears to have occured with some other gymnosperm species, but development was limited to embryoids and proembryos.
In spite of substantial effort over the years, gametophyte culture has progressed very slowly with gymnosperms. Nevertheless some of the recent work is encouraging, as complete regeneration is now repeatable with a few species. The availability of regenerated material is a major condition for a better understanding of the technical and physiological problems which presently limit the haplo-methods in gymnosperms.
Key words: regeneration, tissue culture, gametophyte, gymnosperms