Monoterpenes from the essential oil from Brazilian propolis affect seedling cellular elongation

Propolis is a complex mixture of beeswax, resinous and volatile substances produced by honeybees with material collected from plant exudates. The essential oil obtained from a propolis samples from southern Brazil was extracted by hydro-distillation. The yield of oil is high (8.5%), and its major constituents are the monoterpenes α-pinene (86%), β-pinene (12%) and camphene (1%). At 1% concentration, the oil inhibited the germination of lettuce seeds. At 0.25%, the growth speed index and the growth of the hypocotyl–radicle axis reduced substantially. The oil at 0.5% inhibited the elongation of procambial cells and shifted the elongation of the ground meristem cells axially to radially. Hence, the elongation zone assumed a stratified arrangement. In radicles from seeds treated with oil at 1%, a radially directed cell elongation took place in the root cap, protoderm and procambium, preventing the root to protrude. Intercellular spaces appeared between layers of cells of the ground meristem. The anatomical changes observed might be an effect of monoterpenes, either promoting the production of ethylene or affecting the sensitivity of meristem cells to this regulator.