THE PHYSICAL AND CHEMICAL ENVIRONMENT OF THE DEVELOPING EMBRYO OF PINUS-RESINOSA

The relationship between changes in soluble protein, hexose sugar, total lipid concentration, and osmotic potential occurring in gametophytic supernatant of Pinus resinosa Ait, during in vivo embryogenesis was measured. The effects of varying sucrose levels of culture medium on in vitro embryo and gametophyte development were examined. Increases in embryo volume, and fresh and dry weight of the female gametophyte during in vivo embryogenesis coincide with increasing levels of soluble protein, hexose sugar, and total lipid in the gametophytic supernatant. In contrast, osmotic potential of the supernatant increased only slightly between the zygote and proembryo stages of embryo development, and remained constant thereafter. Gametophytes plus embryos grown in vitro achieved dry weights approaching those of in ovulo gametophytes on media containing levels of sucrose up to 21%. Gametophytes on media with sucrose concentrations up to 21% also resembled normal in ovulo gametophytes in appearance. However, embryo development appeared to be suspended on treatment media containing from 9% to 21% sucrose, while embryos degenerated on media with constant sucrose levels of 3% and 6%. A treatment medium containing approximately 12% sucrose would provide an osmotic environment that duplicates that found in ovulo. While greater sucrose levels promoted more normal gametophyte development in Pinus resinosa, we failed to achieve complete development of the embryo in vitro. Conclusions and implications drawn from these results are discussed.