EFFECT OF ABSCISIC-ACID, OSMOTICUM AND DESICCATION ON 11S STORAGE PROTEIN GENE-EXPRESSION IN SOMATIC EMBRYOS OF WHITE SPRUCE

The effect of ABA, non-permeating osmoticum and late stage maturation drying on 11S storage protein gene expression in white spruce somatic embryos was investigated. A partial cDNA clone encoding the beta-polyp eptide of white spruce 11S legumin-like seed storage protein (named be ta-coniferin) was employed as a probe. Northern blot analyses demonstr ated that in somatic embryos matured with 16 mu M ABA and 7.5% PEG, th e levels and patterns of accumulation of transcripts during early and mid-stages of embryogenesis were comparable to those observed in zygot ic embryos at a similar morphological stage. Steady-state levels of co niferin transcripts declined when late stage somatic embryos were expo sed to a desiccation treatment. Levels of coniferin transcripts in som atic embryos matured with 16 mu M ABA and low osmoticum were substanti ally lower than those of somatic embryos matured with 7.5% PEG and 16 mu M ABA. Increasing concentrations of ABA resulted in higher levels o f accumulation of coniferin transcripts, however, the levels in somati c embryos matured with 32 mu M ABA and low osmoticum remained lower th an those of somatic embryos matured on 16 mu M and 7.5% PEG indicating that the latter treatment is optimum for induction and accumulation o f coniferin transcripts. The similarity of 11S storage protein gene ex pression in somatic embryos with zygotic embryos, along with their sen sitivity to ABA and osmoticum indicates that somatic embryos may provi de a useful system to facilitate studies of gene regulation in conifer s.