Phytotoxicity evaluation of poly (ɛ-caprolactone) nanocapsules prepared using different methods and compositions in Brassica juncea seeds

The objective of this study was to analyze the phytotoxic effects of poly (ɛ-caprolactone) (PCL) nanocapsules on mustard (Brassica juncea) seeds. The nanoformulations were prepared using two protocols: PCL nanocapsules containing Tween as a stabilizer (NC TW) and PCL nanocapsules containing poly(vinyl alcohol) (PVA), a polymer that has emulsifying properties (NC PVA). Two experimental systems were used (nanoformulations sprayed on the substrate and as seed treatment), each one in a factorial scheme with two formulations (NC TW and NC PVA) and five dilutions (0%, 25%, 50%, 75%, and 100% of the stock formulation). In general, intermediary concentrations of NC TW showed higher phytotoxicity than NC PVA, as indicated by sharper reductions in germination and increases in the percentage of abnormal seedlings. However, in the substrate treatment, NC PVA (100%) led to a sharper reduction in germination than NC TW in the same dilution. NC TW-treated seeds presented greater water absorption. In an additional assay with nanocapsules labeled with a fluorescent probe (rhodamine B), NC PVA-treated seeds showed higher fluorescence intensity in the seed coat. In the case of NC TW-treated seeds, the fluorescence signal tended to move to the seed interior as the nanocapsule levels increased. Moreover, the seed treatment with this formulation induced sharper increases in water uptake by the seeds than NC PVA. The different effects induced by NC TW and NC PVA could be related to the different characteristics of the nanocapsules, as the lower size and more negative charge of NC TW might have favored their entrance into the seeds.