Abstract
Lanthanum (La) is a chemically active and naturally occurring rare-earth element (REE) known to exert both beneficial and deleterious effects to plant growth and physio-biochemical functions. Not much information is available to substantiate the integrative role of salicylic acid (SA) and silicon (Si) in alleviating La toxicity in plants. Therefore, the current study was planned to evaluate the role of SA and Si in mitigating the La toxicity in mustard (Brassica juncea L.) seedlings. Different physiological and biochemical parameters like the estimation of chlorophyll, nutrients content and osmotic compounds, and analysis of antioxidative enzymes and non-antioxidative enzymes were used in this study. Mustard seedlings grown under La toxicity conditions exhibited reduced growth attributes and impaired photosynthetic metabolism. However, the combined application of SA and Si synergistically suppressed hydrogen peroxide (H2O2) content, electrolytic leakage, malondialdehyde and improved the content of nutrients (nitrogen, phosphorus, potassium, sulfur, calcium and Si). Upregulation of antioxidant enzymes superoxide dismutase, ascorbate peroxidase content, glutathione reductase and glutathione S-transferase , nutrient homeostasis, and carbonic anhydrase (CA) activity, ribulose-1,5-bisphosphate carboxylase/oxygenase (involved in CO2 fixation), and betaine aldehyde dehydrogenase , was also accompanied by increased accumulation of glycine betaine and cysteine in SA plus Si-treated seedlings. Present evidence reveals the beneficial role of SA and/or Si in the mitigation of La toxicity being attained through the improvement of physiological and biochemical mechanisms, redox regulation and photosynthetic efficiency in mustard (Brassica juncea L.) seedlings. Thus, obtained results postulate that the combined application of SA and Si is effective in mitigating the toxic effect of La on the growth and physio-biochemical parameters of mustard seedlings.