Regulation byABAof,-Conglycinin Expression inCultured Developing Soybean Cotyledons' Received forpublication February 2,1985 andinrevised formJuly 8,1985

Theregulation ofcotyledon-specific geneexpression byexogenously applied abscisic acid (ABA)wasstudied indeveloping cultured cotyledons ofsoybean (Glycine maxL.Merr. cvProvar). Whenimmature cotyledons werecultured inmodified Thompson's medium, theaddition ofABA resulted inanincreased concentration ofthej6-subunit ofy-conglycin, oneofthemajor storage proteins ofsoybean seeds. Theamount ofthe a'-anda-subunits of$-conglycinin wasrelatively unaffected bytheABA treatment. Whenfluridone, aninhibitor ofcarotenoid biosynthesis that hasbeenshowntodecrease ABAlevels inplant tissues, wasadded to themedium thelevel ofABAandthe#-subunit decreased inthecotyledons. Increasing theconcentration ofsucrose intheculture medium caused anincrease intheconcentration ofABAand#-subunit inthe cotyledons. Wheninvitro translation products fromRNAisolated from cotyledons cultured withABAwereimmunoprecipitated with antiserum against l-conglycinin, there wasanincreased amountofpre-li-subunit polypetide compared tothetranslation products fromRNAisolated from control cotyledons. Thepre-l-subunit polypeptide wasnotdetected in translation products fromRNA isolated fromfluridone-treated cotyledons. Nucleic acidhybridization reactions showed that thelevel of,subunit mRNA washigher inABA-treated cotyledons compared tothe control, andwaslower inthefluridone-treated cotyledons. We have shownthat exogenous ABAisable tomodulate theaccumulation ofthe li-subunit of,l-conglycinin indeveloping cultured soybean cotyledons. Developing soybean seeds accumulate twomajor groups of storage proteins; ,B-conglycinin which hasasedimentation coefficient ofabout7Sandglycinin whichhasasedimentation coefficient ofabout11S. ,3-Conglycinin isaglycoprotein composed ofthree major subunits; a'(76kD), a(72kD), andfi(53 kD).Inthecultivar Provar, thea'-anda-subunits begin to accumulate 19dafter flowering whentheseeds areapproximately 8mm inlength. The,B-subunit accumulates atalater stage ofdevelopment, 21dafter flowering, whentheseeds are approximately 10mm inlength (20). Theaccumulation of storage proteins islargely regulated atthelevel ofgenetranscription. ThemRNAsforsoybean seedstorage proteins arefound only indeveloping seeds andcannot bedetected inthecytoplasm orthenuclei ofleaves (8,9).Thea'-anda-subunits of11conglycinin begin toaccumulate several days after themRNAs arefirst detected (20). Although itisthought that theprimary regulation ofdevelopmental expression ofstorage proteins in