DIFFERENTIAL REGULATION OF THE EXPRESSION IN TRANSGENIC TOBACCO OF THE GENE FOR BETA-GLUCURONIDASE UNDER THE CONTROL OF THE 5'-UPSTREAM REGIONS OF 2 CATALASE GENES FROM CASTOR BEAN

The regulatory functions of the 5'-flanking regions of two genes for c atalase (cat1 and cat2) from castor bean were analyzed in transgenic t obacco plants that carried fusion constructs that included the gene fo r beta-glucuronidase (GUS) for Escherichia coli. Dry mature seeds from transgenic plants carrying the CAT1-GUS or CAT2-GUS constructs, in wh ich the GUS gene was fused to the 5'-flanking region of cat1 or cat2, respectively, contained significant GUS activity, indicating that the promoters of cat1 and cat2 were active during seed development. GUS ac tivity increased in response to germination in the seeds of transgenic tobacco that carried CAT1-GUS, as well as in those that carried CAT2- GUS. During the post-germinative stage the GUS activity directed by CA T2-GUS increased still further, whereas that directed by CAT1-GUS decr eased, The changes in GUS activity in the transgenic tobacco plants th at carried CAT1-GUS and CAT2-GUS were similar to the changes in the le vels of transcripts of cat1 and cat2, respectively, in castor bean. Th e results suggest that the expression of cat1 and cat2 in the germinat ing seeds and postgerminative seedlings is regulated mainly at the lev el of transcription. However, the distribution of GUS activity among t he organs of the transgenic tobacco seedlings and plantlets, which was examined by histochemical staining and by enzymatic assays of tissue extracts, was not identical to that of transcripts of cat1 and cat2 in castor bean. Histochemical analysis also revealed the interesting spa tial regulation of the expression of the promoter of cat2 in the trans genic tobacco seedlings.