STORAGE PROTEIN GENE-EXPRESSION IN ZYGOTIC AND SOMATIC EMBRYOS OF INTERIOR SPRUCE

Storage protein gene expression was compared between zygotic and somat ic embryos of interior spruce (Picea glauca/engelmanii complex). Somat ic embryos, grown on medium containing 40 mu M or 10 mu M abscisic aci d (ABA), and zygotic embryos accumulated 11S legumin, 7S vicilin and 2 S albumin storage proteins. Zygotic embryos displayed a rapid, transie nt period of storage protein accumulation, while somatic embryos diffe rentiated on 40 mu M ABA displayed a more prolonged, gradual accumulat ion, with some accumulation still evident after 9 weeks of maturation. Somatic embryos on 10 IJ M ABA accumulated storage proteins initially , but these were rapidly degraded as the embryos germinated precocious ly. Legumin, albumin and vicilin transcripts were detectable in torped o stage zygotic and somatic embryos, and increased during embryo devel opment. Transcript levels in zygotic embryos increased during cotyledo n development, but following maximum dry weight accumulation and moist ure loss, transcripts declined rapidly to low levels. In contrast, som atic embryos on 40 mu M ABA had high transcript levels for a prolonged period. These levels were still present after 9 weeks of maturation. A decline in storage protein transcripts similar to zygotic embryos wa s apparent following a mild drying treatment. These results suggest th at a decline in storage protein transcripts is stimulated by embryo dr ying during the later stages of conifer embryogenesis. Low levels of s torage protein transcripts also appeared in somatic embryos on 10 mu M ABA, but declined during precocious germination. Osmotic stress induc ed storage protein and storage protein transcript accumulation. This c ould be partially inhibited by inclusion of the ABA biosynthetic inhib itor, fluridone. However, endogenous ABA levels did not differ signifi cantly between embryos cultured in the presence or absence of fluridon e.