SEED COAT PERMEABILITY AND UPTAKE OF APPLIED SYSTEMIC COMPOUNDS

Efficacy of systemic seed treatments depends on the ability of applied chemical compounds to penetrate through the seed coat and be transported into the seedling. The objective of the present work was to study how chemicals diffuse through the seed coat and whether or not they are able to penetrate the embryo of different vegetable crop seeds. Seed coat permeability properties of snap bean (Phaseolus vulgaris L.) and cucumber (Cucumis sativus L.) were selected to represent different morphology and composition, including the presence of a semi-permeable layer. Fluorescent tracer was employed to mimic the movement of seed treatments and for visualization of chemical movement. Fluorescent tracer was applied to seeds by a dry powder coating, placed in moistened sand at 20°C. Seeds were removed, and studied prior to and after germination. The location and intensity of fluorescence in hand dissected, imbibed seeds and developing seedlings were observed under long-wavelength UV light. Fluorescent tracer was able to cross the snap bean seed coat and to be taken-up by seed embryo tissues. In contrast, cucumber seed coats were impermeable to fluorescent tracers supporting the hypothesis of an 'endosperm-perisperm envelope' surrounding the embryo. Two pathways of systemic compounds uptake was observed: through the seed coat to the embryo (permeable snap bean seeds) and through emerging seedling tissues after germination occurred (cucumber seeds).