TISSUE-SPECIFIC AND LIGHT REGULATION OF A LARCH RIBULOSE-1,5-BISPHOSPHATE CARBOXYLASE PROMOTER IN TRANSGENIC TOBACCO

A chimeric gene composed of an eastern larch (Larix laricina (Du Roi) K. Koch) ribulose-1,5-bisphosphate carboxylase (RbcS) promoter linked to the beta-glucuronidase (GUS) coding sequence was transferred to tob acco (Nicotiana tabacum (L.)) via Agrobacterium tumefaciens transforma tion. Based on GUS activity the larch RbcS promoter functioned in an o rgan-specific and light-regulated manner. Histochemical analysis revea led high levels of GUS activity in photosynthetically active tissues a nd low or undetectable activity in xylem and root tissues. Fluorometri c analysis of GUS activity demonstrated that the larch RbcS promoter w as expressed at a 10-fold higher level in leaf blades than in root tis sue. Light-grown transgenic plants expressed GUS at a two-fold higher level than dark grown individuals. These results suggest evolutionary conservation of tissue-specific RbcS promoter activity between gymnosp erms and angiosperms but only weak conservation of the transduction me chanism for light regulation.