Flowering plants (angiosperms) constitute the most diverse and successful group of plants living on earth, yet many aspects of their evolutionary origins from more primitive seed-bearing plants are poorly understood. Plant biologists have proposed that much of the evolutionary success of angiosperms can be attributed to their unusual and highly derived pattern of sexual reproduction. Specifically this involves a double fertilization process, the egg nucleus fusing with one pollen-borne sperm nucleus to produce the zygote of the embryo, and a second fertilization event involving another pollen-borne nucleus. The product of the second fertilization develops into a highly efficient nutrient-garnering tissue called endosperm, which functions to nourish the developing embryo inside the seed. Until now little effort has been devoted to understanding how the distinctive reproductive process of double fertilization might have evolved. Dr. William Friedman of the University of Georgia will examine patterns of sexual reproduction among members of the genus Ephedra, suspected of being the most closely related living group of seed-bearing gymnosperms. Although most aspects of fertilization in Ephedra are not well understood, there are indications that events similar to the process of double fertilization in angiosperms may occur in this genus. Using modern techniques and apparatus for DNA measurement and for microscopic analysis, Dr. Friedman will investigate reproduction in several representative species of Ephedra, analyzing the ontogenetic patterns of gamete-formation, fertilization, and early development of the embryo. Similarities may reveal clues about the intermediate steps leading to angiosperm double fertilization and help in understanding its adaptive significance.
