Legacy effects of heavy metal exposure on tobacco germination success

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Jenna Crawford, Biology, Norfolk State University, Norfolk, VA

Background/Question/Methods
Human industrial and technological growth have left many marks on the world in which we live. We constantly deal with relic and modern crises of climate and environment. One of the most complex of our legacies is the contamination of terrestrial and aquatic systems with a cocktail of naturally occurring elements and compounds as well as synthetic ones. Ecotoxicological studies have investigated a broad range of compounds, on a vast number of species, in highly varied systems. Immediate responses to contaminants have received the bulk of the focus; however, we must not forget the potential for legacy effects on biota as well. This study compared germination success of tobacco seeds with healthy parentage to germination success of seeds from plants grown in contaminated soils. Seed stock was obtained from Tobacco (Nicotiana tobacum var. Cubana Corojo) grown in the Norfolk State Greenhouse. Plants were exposed to 0 ppm (Reference), 25 ppm Cd, 50 ppm Cd, 400 ppm Pb, 1200 ppm Pb, 1300 ppm Zn, or 4500 ppm Zn. Concentrations were chosen from average high and low reference values presented in the literature for each element. Seeds were harvested from fully mature pods and stored at 4℃ in the dark until tested. Seeds from control plants were then exposed to the same levels of contamination and germination was monitored for 7 days. Seeds from plants exposed to metals were germinated without exposure to contamination and also monitored for 7 days.
Results/Conclusions
This study found that there was a greater relative reduction in germination for seeds from contaminated parentage than Reference seeds exposed to the contaminants directly. Seeds from healthy parents exposed to metals directly only exhibited significant reductions when high levels of cadmium were present, while seeds from parent plants exposed to high levels of all three metals tested showed significant reductions. This illustrates that there is great potential for contaminated systems to not only affect those organisms currently residing therein but also impact the success of their offspring even if they travel to cleaner environments.