FIELD PERFORMANCE AND HEAVY-METAL CONCENTRATIONS OF TRANSGENIC FLUE-CURED TOBACCO EXPRESSING A MAMMALIAN METALLOTHIONEIN-BETA-GLUCURONIDASEGENE FUSION

Cadmium (Cd) is a nonessential heavy metal that can cause acute and ch ronic illness in humans. Some plant species such as tobacco (Nicotiana tabacum L.) tend to accumulate high levels of Cd in leaf tissue, the consumed portion of the plant. Tissue-specific expression of mammalian metallothionein has been suggested as a means of partitioning Cd in n onconsumed portions of transgenic plants. The purpose of the experimen t reported here was to evaluate Cd concentration and agronomic perform ance of four field-grown transgenic tobacco lines harbouring a metallo thionein-beta-glucuronidase (MG) gene fusion driven by the constitutiv e 35S promoter of cauliflower mosaic virus. The trial was grown in a r egion of Canada known to have high background levels of Cd. The agrono mic evaluation showed that some of the transgenic lines were equal to, while others performed more poorly than, the untransformed control fo r yield, days to flower, and leaf number. Gene expression measured by beta-glucuronidase activity showed that all of the transgenic lines ex pressed the MG gene in the upper portion of the plant. One line did no t express the MG gene in the roots. Cd levels in the leaf tissue of tr ansformed lines were not significantly different from the untransforme d control.