Abscisic acid and the regulation of synthesis of specific seed proteins and their messenger RNAs during culture of soybean embryos.

The ability of soybean (Glycine max (L.) Merr.) embryos cultured in vitro in the absence of abscisic acid (ABA) to germinate precociously increased as the embryos matured. Exogenous ABA prevented precocious germination at all stages of development, concentrations below 10(-5) M being partially effective. Growth (fresh weight increase) of mid-maturation embryos was dependent on ABA, and such embryos required ABA for continued synthesis of storage proteins during culture. Two complementary-DNA clones for different members of the family of 11S storage proteins, and one for the 7S storage proteins were used in Northern blot hybridizations to analyze the effects of ABA on the levels of the 11S and 7S mRNAs. In addition, filter hybridizations with in-vivo-labeled [(3)H]polyadenylated RNA to the cloned DNA for one of the 11S proteins were carried out to study transcription of 11S mRNA. Midmaturation embryos cultured with ABA continued to transcribe mRNAs for the storage proteins during the 21 d of culture studied, whereas in the absence of ABA these mRNAs disappeared from the cotyledons within about 5 d. The optimum concentration of ABA for the synthesis of storage-protein mRNAs was 10(-5) M. The effect of ABA on the concentration of 11S mRNAs was stage-dependent. Abscisic acid caused a decrease in the mRNA in embryos cultured at the cotyledon stage; it was necessary for high levels of the mRNA to be achieved in early- and mid-maturation embryos; and it did not reverse the decline in the mRNA levels in embryos cultured at the late-maturation stage.