Effect of nanosized anatase TiO2 on germination, stress defense enzymes, and fruit nutritional quality of Abelmoschus esculentus (L.) Moench (okra)

Due to wide-scale generation/use of titanium dioxide (TiO2) nanoparticles, significant release into agricultural soil is inevitable. This has caused great ecotoxicological concern due to their unclear fate in plants, most especially food crops. This study aimed to compare the impact of anatase nano-TiO2 of two primary diameters (nTiO(2) [50 nm] and bTiO(2) [68 nm]) on stress enzymes and seed nutritional quality of okra (Abelmoschus esculentus) plant. Compared to control, bTiO(2) significantly promoted seed germination in okra while chlorophylls were only enhanced significantly by nTiO(2) and reduced by bTiO(2). The results of biochemical experiments implied that both nano-TiO2 particles significantly reduced ascorbate peroxidase (APX) and glutathione reductase (GR) activity levels in roots. Conversely in leaves, APX activity level was significantly reduced by the both nano-TiO2 particles, while GR activity was promoted. Interestingly, both nano-TiO2 particles significantly increased superoxide dismutase activity in roots and leaves, indicating that nano-TiO2 induced toxicity to okra plant. The accumulation of malondialdehyde in leaves was significantly high in okra plants exposed to bTiO(2), and this underpins the fact that the large-sized nano-TiO2 portends phytotoxicity to the leaves. In this study, the degree of response of stress enzymes to nano-TiO2 was particle size. Fruit quality analysis indicated a decrease in Ca, Mg, and Fe contents which was particle size-dependent and dose-dependent. In addition, the proximate compositions (except carbohydrate) of fruits were all negatively altered by both nano-TiO2 particles. Conclusively, the results suggest that particle size is a factor in the phytotoxicity and the individual effect of both nano-TiO2 particles on okra plant was dose-dependent.