In principle, just about any substance that poisons plants or otherwise retards growth could be used for selection, as long as there's a resistance gene to go with it. University of Georgia geneticist Richard Meagher engineers plants to phytoremediate heavy metals in contaminated soils. Meagher says merA can be used as a marker to select transformed plantlets on medium containing mercuric chloride. Georgia patented the system in 1996, and Meagher sees commercial interest, particularly for pine transformation. For plantlets to grow from transformed tissue, they need exogenous hormones in the form of auxin and cytokinin.
Plant scientists can construct selection systems around that requirement.
12 Chua uses a gene from Agrobacterium tumefaciens encoding isopentenyl transferase, which synthesizes natural cytokinin, but adds a promoter sequence to turn on gene activity under the influence of the steroid dexamethazone. Chua, who just patented the procedure, has tried it on tobacco and lettuce. As another plant biologist put it, it's the wave of the future. S Barry A. Palevitz is a contributing editor for The Scientist. F.T. Okkels et al.