Embryogeny of gymnosperms: advances in synthetic seed technology of conifers

Abstract

Synthetic seed technology requires the inexpensive production of large numbers of high-quality somatic embryos. Proliferating embryogenic cultures from conifers consist of immature embryos, which undergo synchronous maturation in the presence of abscisic acid and elevated osmoticum. Improvements in conifer somatic embryo quality have been achieved by identifying the conditions in vitro that resemble the conditions during in ovulo development of zygotic embryos. One normal aspect of zygotic embryo development for conifers is maturation drying, which allows seeds to be stored and promotes normal germination. Conditions of culture are described that yield mature conifer somatic embryos that possess normal storage proteins and fatty acids and which survive either partial drying, or full drying to moisture contents similar to those achieved by mature dehydrated zygotic embryos. Large numbers of quiescent somatic embryos can be produced throughout the year and stored for germination in the spring, which simplifies production and provides plants of uniform size. This review focuses on recent advances in conifer somatic embryogenesis and synthetic seed technology, particularly in areas of embryo development, maturation drying, encapsulation and germination. Comparisons of conifer embryogeny are made with other gymnosperms and angiosperms.