| Abstract | We examined endogenous abscisic acid [(+)-ABA] amounts and mRNA populations in white spruce (Picea glauca (Moench) Voss) somatic embryos in liquid suspension culture during a pretreatment prior to induction of maturation with exogenous (+)-ABA. The pretreatment consisted of removal of 2,4-dichlorophenoxyacetic acid (2,4-D) from the multiplication medium for 7 days. The removal of 2,4-D resulted in a slight increase in endogenous ABA in pretreated tissues compared to nonpretreated tissues at the end of the 7-day pretreatment period (42.4 versus 20.0 pg mg−1 lyophilized tissue). Altered gene expression patterns were observed as early as one day after the start of the pretreatment, with more than 17 new polypeptides found in pretreated tissues. The influence of pretreatment continued to be observed after tissues were transferred to ABA-containing maturation medium. By comparing mRNA populations in pretreated and nonpretreated tissues cultured on either ABA-containing or ABA-free maturation medium, at least 12 mRNAs were observed to be induced by ABA, among which three polypeptides were ABA inducible only in pretreated tissues. |
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