EMBRYOGENY OF GYMNOSPERMS - ADVANCES IN SYNTHETIC SEED TECHNOLOGY OF CONIFERS

Synthetic seed technology requires the inexpensive production of large numbers of high-quality somatic embryos. Proliferating embryogenic cu ltures from conifers consist of immature embryos, which undergo synchr onous maturation in the presence of abscisic acid and elevated osmotic um. Improvements in conifer somatic embryo quality have been achieved by identifying the conditions in vitro that resemble the conditions du ring in ovulo development of zygotic embryos. One normal aspect of zyg otic embryo development for conifers is maturation drying, which allow s seeds to be stored and promotes normal germination. Conditions of cu lture are described that yield mature conifer somatic embryos that pos sess normal storage proteins and fatty acids and which survive either partial drying, or full drying to moisture contents similar to those a chieved by mature dehydrated zygotic embryos. Large numbers of quiesce nt somatic embryos can be produced throughout the year and stored for germination in the spring, which simplifies production and provides pl ants of uniform size. This review focuses on recent advances in conife r somatic embryogenesis and synthetic seed technology, particularly in areas of embryo development, maturation drying, encapsulation and ger mination. Comparisons of conifer embryogeny are made with other gymnos perms and angiosperms.