GENOTYPIC AND DEVELOPMENTAL REGULATION OF TRANSIENT EXPRESSION OF A REPORTER GENE IN SOYBEAN ZYGOTIC COTYLEDONS

Processes involved in transformation of regenerable soybean (Glycine m ax (L.) Merrill) immature zygotic cotyledons were studied by assaying the transient expression of the beta-glucuronidase gene driven by the 35S promoter and terminated at the 3' end by the soybean 7S storage pr otein gene. The plasmid containing the chimeric gene was delivered to the cotyledons via particle bombardment 900 PSI. Zygotic cotyledons fr om six soybean varieties were tested for transient expression of the b eta-glucuronidase gene. The level of reporter gene expression differed between genotypes. The genotypes could be classified as high, fair or poor expressors. Cotyledons from different genotypes were then bombar ded at 650, 900 or 1100 PSI. GUS expression varied among genotypes ind ependently of the pressure of bombardment. Finally, the ability of cot yledons to express the reporter gene depended on the developmental sta ge of the seed from which it was excised with the younger stage being the least responsive. However, genotypic specific expression remained after controlling for developmental stage of the cotyledons.