Alleviation of nickel toxicity in finger millet (Eleusine coracana L.) germinating seedlings by exogenous application of salicylic acid and nitric oxide

This study investigated the effect of salicylic acid (SA) and sodium nitroprusside (SNP; NO donor) on nickel (Ni) toxicity in germinating finger millet seedlings. Fourteen-day-old finger millet plants were subjected to 0.5 mmol L− 1 Ni overload and treated with 0.2 mmol L− 1 salicylic acid and 0.2 mmol L− 1 sodium nitroprusside to lessen the toxic effect of Ni. The Ni overload led to high accumulation in the roots of growing plants compared to shoots, causing oxidative stress. It further reduced root and shoot length, dry mass, total chlorophyll, and mineral content. Exogenous addition of either 0.2 mmol L− 1 SA or 0.2 mmol L− 1 SNP reduced the toxic effect of Ni, and supplementation with both SA and SNP significantly reduced the toxic effect of Ni and increased root and shoot length, chlorophyll content, dry mass, and mineral concentration in Ni-treated plants. The results show that oxidative stress can be triggered in finger millet plants by Ni stress by induction of lipoxygenase activity, increase in levels of proline, O2•− radical, MDA, and H2O2, and reduction in the activity of antioxidant enzymes such as CAT, SOD, and APX in shoots and roots. Exogenous application of SA or SNP, specifically the combination of SA + SNP, protects finger millet plants from oxidative stress observed under Ni treatment.