Non-toxicity of nano alumina: A case on mung bean seedlings

Wide use of Al2O3 nanoparticles (NPs) leading to their possible escape into environment and their interaction with living organisms demands immediate attention. We evaluated impact of nanoparticulate (Al2O3-NPs) and ionic (Al3+) forms of aluminium on early seedling growth of Vigna radiata. While Al3+ inhibited growth of seedlings, Al2O3-NPs did not affect it negatively. Unlike enhancement in proline, malondialdehyde and H2O2 levels in roots and shoots induced by Al3+, these stress markers remained unaltered by Al2O3-NPs. No signs of membrane damage were recorded in roots of seedlings raised in presence of Al2O3-NPs; this was witnessed from insignificant electrolyte leakage and Evans blue uptake. Activities of antioxidant enzymes, i.e., superoxide dismustase, catalase, guaiacol peroxidase in root and shoot were enhanced by Al3+. However, they were unaffected by Al2O3-NPs. Al3+ enhanced levels of non-protein thiols, phenolics and ascorbate, with no alterations induced by Al2O3-NPs. These findings revealed that, Al2O3-NPs did not induce oxidative stress in seedlings. Seedlings raised in Al3+ showed higher uptake of Al than those grown in Al2O3-NPs; Al content was higher in roots. Al was not detected in shoots of seedlings grown in Al2O3-NPs. Lower translocation of Al in seedlings raised in Al2O3-NPs was due to adsorption/restriction of Al2O3-NPs on root surface. Al3+ caused ruptures on root epidermis of seedlings and inhibited root-hair formation, whereas no structural damage was caused by Al2O3 NPs. Our findings revealed that while ionic Al is highly toxic, nanoparticulate form of Al is non-toxic to growth of V. radiata.