Enhanced growth and antioxidant efficiency of Vigna radiata seedlings in the presence of titanium dioxide nanoparticles synthesized via the sonochemical method

Nanosized titanium dioxide (nTiO(2)) is one of the most diverse nanomaterials available today but inconclusive studies on the effects of nTiO(2) on plants are withholding its successful application in agriculture. In the present work, an attempt has been made to evaluate the interaction of nTiO(2) with Vigna radiata (L.) Wilczek from the seed germination stage until the plants were 14 days old. TEM analysis revealed that nTiO(2) was synthesized in the size range of 1-10 nm and X-ray diffraction (XRD) analysis confirmed the crystal structure. The plants were raised hydroponically in nutrient solution spiked with two different concentrations of nTiO(2) (10 and 100 mg L-1). Inductively coupled plasma mass spectrometry (ICP-MS) results established the accumulation of nTiO(2) in leaves. In response to the presence of nTiO(2), V. radiata plants performed better as indicated by their increased seed germination, root and shoot length, higher fresh and dry weight and elevated chlorophyll and flavonoid contents. Germination percentage of V. radiata seeds increased by about 22% at 10 mg L-1 and 14% at 100 mg L-1 nTiO(2) concentration. Maximum stimulation of total chlorophyll, flavonoids and phenolic contents was observed at 100 mg L-1 nTiO(2) concentration in 7-day old plants, where an astonishing 8 fold increase in chlorophyll, 3 fold increase in flavonoids and 2 fold increase in phenolics was observed. However, a decrease in carbohydrate and protein contents and an increase in lipid peroxidation also marked the presence of mild oxidative stress that was neutralized by increased activity of antioxdant enzymes namely catalase, glutathione reductase and glutathione-s-transferase. The activity of superoxide dismutase was more or less stable while glutathione peroxidase activity reduced compared to the control plants. The higher ABTS and DPPH free radical scavenging activities of the nTiO(2) treated plants also supported effective neutralization of free radicals.