Effects of nanosized titanium dioxide on the photosynthetic metabolism of fenugreek (Trigonella foenum-graecum L.).

The potential toxicity of nanoparticles in plants is scarce and contradictory. Despite the diversity of research efforts, a detailed explanation of the TiO2 NPS effects in plant photosynthesis is still missing. The present work gives a new approach to examine the impact of the TiO2 NPs on crop production (development and photosynthesis) and plant protection (tolerance and defense systems) in fenugreek (Trigonella foenum graecum L.). Seedlings were assessed in greenhouse trials to estimate the influence of TiO2 NPs on physiological characters for 16 days. They were treated with TiO2 NPs at a size less than 20nm. The results revealed that there were no significant effects on seedlings growth and biomass of stem, but a decrease in the fresh weight of leaves after TiO2 NPs treatment. Plants treated with 100mg·L-1 of TiO2 NPs presented a reduction and chlorosis in leaf area due to a significant decrease in the chlorophyll a and b contents. The highest value of the photosynthetic pigments was recorded at 50mg·L-1 of TiO2 NPs. However, the treatment with 100mg·L-1 of TiO2 NPs caused a decrease in the levels of chlorophyll a, b and of carotenoids. Both doses of TiO2 NPs induced an accumulation of anthocyanins compared to the control after 16 days of seedling development. A nano-stress significantly decreased the flavonoids level, but increased that of polyphenols compared to control after 16 days of exposure. The decrease in the translocation ratio of flavonoids suggests that many of them contain an enediol group, which suggests that they may act as bidentate ligands for anatase TiO2 NPs. Accordingly, nano-stressed leaves exhibited significantly enhanced GPOX, CAT and APX activity levels. On the contrary, GPOX and CAT activities were reduced substantially in stems treated with 100mg·L-1 TiO2 NPs. The accumulation of MDA was found to be higher in stems than in leaves. This could be explained by the accumulation of nanoparticles in different organs; it could be that the stems are the favored targets of nanoparticles. These results underline the necessity for a deeper estimation of nanoparticle ecotoxicity and particularly concerning their interaction with plants.