Heavy Metals and Seed Germination in Medicinal and Aromatic Plants

Abstract

Phytoremediation has been suggested as a solution to heavy metal—polluted soils, but the choices of suitable plant species for phytoremediation have been limited. Medicinal and aromatic plants appear to be excellent selections for these plantings, since these plants are grown for economically valuable secondary products (essential oils), not for food or feed. Preliminary research indicates that heavy metals are not accumulated in essential oils, permitting the oil to be used commercially. Productivity of some, but not all aromatic plants was reduced, however, by the heavy metals. The objective of our experiment was to distinguish the mechanism of heavy metal tolerance of plants using germinating seeds of medicinal and aromatic plant species. Seeds from medicinal and aromatic plants were germinated in solutions with selected levels of heavy metals (cadmium at 6 and 10 (μg·L-1; copper at 60 and 150 μg·L-1; lead at 100 and 500 μg·L-1; zinc at 400 and 800 μg·L-1) and in distilled water. Tests on Anethum graveolens L., Carum carvi L., Cuminum cyminum L., Foeniculum vulgare Mill., Pimpinella anisum L., Ocimum basilicum L., and the hyperaccumulator species Brassica juncea L. and Alyssum bertolonii established that different plant species reacted in different ways to the heavy metals. For example, cadmium did not decrease seed germination of Alyssum, O. basilicum, and B. juncea compared with germination in water but did decrease germination of C. cyminum. Lead did not affect germination of A. bertolonii and B. juncea as compared with water but did negatively affect germination of P. anisum, F. vulgare, and C. cyminum. Except for B. juncea, F. vulgare, and C. cyminum, copper had a negative effect on germination. Zinc decreased germination in all tested species except B. juncea.