Factors influencing the conversion of isolated mature zygotic embryos of Pinus radiata D. Don into plantlets were investigated. Nutritional factors were critical to this conversion. The optimum medium strength was half-strength medium consisting of modified Quoirin and Le Poivre salts (von Arnold and Eriksson, 1981) and Schenk and Hildebrandt (1972) vitamins. Sucrose (3%), glucose (2-3%) and fructose (2-5%) could serve as carbon sources for this conversion. In general., a few significant benefits were found with the addition of organic nitrogen sources tested on the development of isolated embryos into plantlets. Nearly all plant growth regulators tested were not beneficial for this conversion, and some of them had a negative effect. Only gibberellic acid (GA(3) at 0.58 muM) seemed to stimulate embryos to germinate a little bit earlier in comparison with the control. Submerging the cotyledons of the isolated embryo into the agar-gelled medium led to better growth in comparison with the control. Embryos cultured in liquid medium grew better but the germination percentage was apparently lower compared with agar-gelled medium. Liquid medium with sponge support could increase the percentage of germinated isolated embryos, but the embryo growth was not comparable to the liquid medium only. The addition of polyethylene glycol 6000 to the liquid medium seemed to increase the germination percentage and had no adverse effect on the growth of isolated embryos. Light could influence embling growth in different ways.
