ASSESSMENT OF STRESS END POINTS IN VIGNA RADIATA SEEDLINGS EXPOSED TO PRE-ACTIVATED TIO2 AND TISIO4 NANOPARTICLES UNDER SOLAR RADIATION
<p class="03-Address"><strong>Objective: </strong>The present study was aimed to evaluate the phototoxic effects of sunlight pre-irradiated/nonirradiated TiO<sub>2</sub>, TiSiO<sub>4</sub> nanoparticles and TiO<sub>2 </sub>bulk powder to Vigna radiata seedlings.</p><p class="03-Address"><strong>Methods</strong><strong>: </strong>Different concentrations (0.05, 0.2, 0.5 and 1.0 g/l) of nano/bulk particles were applied to the germinated seedlings for 24 h and various biochemical end points were assessed. The end points were superoxide dismutase activity, catalase activity, malondialdehyde (MDA) and proline content.</p><p class="03-Address"><strong>Results: </strong>The irradiated nano TiO<sub>2 </sub>was more phototoxic to the seedlings as compared to both the non-irradiated nano TiO<sub>2 </sub>as well as the irradiated/non-irradiated TiO<sub>2</sub> bulk powder, as revealed by the increased level of antioxidant enzymes activity in irradiated TiO<sub>2</sub> nanoparticles treated group. Toxicity in nano TiO<sub>2</sub> group was more confined to the lowest concentration (0.05 g/l). Proline, a well-recognized stress biomarker, was found to increase in all the irradiated as well as the non-irradiated groups in a dose dependent manner (0.20 to 1.0 g/l), offering a different mechanism of toxicity from that of antioxidative enzymes. TiSiO<sub>4</sub> nanoparticles were not found to be phototoxic significantly under either exposure conditions.</p><p class="03-Address"><strong>Conclusion: </strong>The seedlings of the three treatment groups responded variably to the stress biomarkers, indicating that the mode of action of the nanoparticles to the plant was different from that of the bulk particles in irradiated and non-irradiated conditions and was governed by more than a single factor.</p>