Genotypic and developmental regulation of transient expression of a reporter gene in soybean zygotic cotyledons.

Processes involved in transformation of regenerable soybean (Glycine max (L.) Merrill) immature zygotic cotyledons were studied by assaying the transient expression of the β-glucuronidase gene driven by the 35S promoter and terminated at the 3' end by the soybean 7S storage protein gene. The plasmid containing the chimeric gene was delivered to the cotyledons via particle bombardment 900 PSI. Zygotic cotyledons from six soybean varieties were tested for transient expression of the β-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 bombarded at 650, 900 or 1100 PSI. GUS expression varied among genotypes independently of the pressure of bombardment. Finally, the ability of cotyledons to express the reporter gene depended on the developmental stage 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.