The paper describes the use of the Escherichia coli β-glucuronidase (GUS) gene as a sensitive and versatile reporter gene for analyzing gene expression in transformed plants. GUS is used as a gene fusion marker to study the expression of genes in plants. The GUS gene is highly stable and can be detected in plant tissues even after prolonged storage. It is also easily assayed using fluorometric methods, allowing for the detection of very small amounts of transformed plant tissue. GUS is not present in higher plants, making it an ideal marker for gene expression studies. The GUS gene can be fused to various promoters, such as the cauliflower mosaic virus (CaMV) 35S promoter or the promoter of the ribulose bisphosphate carboxylase small subunit (rbcS), to direct the expression of GUS in transformed plants. The expression of GUS can be visualized using histochemical methods, allowing for the localization of gene activity in cells and tissues. The GUS system is highly sensitive and can be used to study gene expression in a variety of plant tissues. The system is also useful for studying the transport and targeting of proteins in plants. The GUS system has been used to study the expression of genes in transformed plants and to monitor the transient expression of chimaeric genes introduced into plant cells. The system is also useful for studying the regulation of gene expression in plants. The GUS system is a valuable tool for studying gene expression in plants and has the potential to be used in a wide range of applications.The paper describes the use of the Escherichia coli β-glucuronidase (GUS) gene as a sensitive and versatile reporter gene for analyzing gene expression in transformed plants. GUS is used as a gene fusion marker to study the expression of genes in plants. The GUS gene is highly stable and can be detected in plant tissues even after prolonged storage. It is also easily assayed using fluorometric methods, allowing for the detection of very small amounts of transformed plant tissue. GUS is not present in higher plants, making it an ideal marker for gene expression studies. The GUS gene can be fused to various promoters, such as the cauliflower mosaic virus (CaMV) 35S promoter or the promoter of the ribulose bisphosphate carboxylase small subunit (rbcS), to direct the expression of GUS in transformed plants. The expression of GUS can be visualized using histochemical methods, allowing for the localization of gene activity in cells and tissues. The GUS system is highly sensitive and can be used to study gene expression in a variety of plant tissues. The system is also useful for studying the transport and targeting of proteins in plants. The GUS system has been used to study the expression of genes in transformed plants and to monitor the transient expression of chimaeric genes introduced into plant cells. The system is also useful for studying the regulation of gene expression in plants. The GUS system is a valuable tool for studying gene expression in plants and has the potential to be used in a wide range of applications.