Regulation by ABA of β-Conglycinin Expression in Cultured Developing Soybean Cotyledons

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Abstract
The regulation of cotyledon-specific gene expression by exogenously applied abscisic acid (ABA) was studied in developing cultured cotyledons of soybean (Glycine max L. Merr. cv Provar). When immature cotyledons were cultured in modified Thompson''s medium, the addition of ABA resulted in an increased concentration of the .beta.-subunit of .beta.-conglycinin, one of the major storage proteins of soybean seeds. The amount of the .alpha.'' and .alpha.-subunits of .beta.-conglycinin was relatively unaffected by the ABA treatment. When fluridone, an inhibitor of carotenoid biosynthesis that has been shown to decrease ABA levels in plant tissues, was added to the medium the level of ABA and the .beta.-subunit decreased in the cotyledons. Increasing the concentration of sucrose in the culture medium caused an increase in the concentration of ABA and .beta.-subunit in the cotyledons. When in vitro translation products from RNA isolated from cotyledons cultured with ABA were immunoprecipitated with antiserum against .beta.-conglycinin, there was an increased amount of pre-.beta.-subunit polypeptide compared to the translation products from RNA isolated from control cotyledons. The pre-.beta.-subunit polypeptide was not detected in translation products from RNA isolated from fluridone-treated cotyledons. Nucleic acid hybridization reactions showed that the level of .beta.-subunit mRNA was higher in ABA-treated cotyledons compared to the control, and was lower in the fluridone-treated cotyledons. We have shown that exogenous ABA is able to modulate the accumulation of the .beta.-subunit of .beta.-conglycinin in developing cultured soybean cotyledons.