Seedcoat Permeability: Uptake and Post-germination Transport of Applied Model Tracer Compounds

The seedcoat permeability, uptake, and transport of model fluorescent tracers were investigated in snapbean (Phaseolus vulgaris), pepper (Capsicum annuum), tomato (Solanum lycopersicum), onion (Allium cepa), cucumber (Cucumis sativus), and lettuce (Lactuca sativa) seeds. Nine fluorescent tracers and one vital stain were selected to represent a diversity of physicochemical properties (lipophilicity, electrical charge, etc.) and to simulate behavior of applied seed treatments. To study seedcoat permeability, tracers were applied to seeds as dry powders, and treated seeds were sown in moistened sand at 20 degrees C and removed after 18 to 24 h, a time before visible germination. Imbibed seeds were dissected and fluorescence (staining) was observed in embryos with a dissecting microscope under ultraviolet (365 nm) or visible radiation. Seedcoat permeability of species to solutes was grouped into three categories: 1) permeable-snapbeans; 2) selectively permeable-tomato, pepper, and onion; and 3) non-permeable-cucumber and lettuce. Systemic tracers that failed to permeate seedcoats during seed imbibition were taken up by roots or hypocotyls after visible germination.