Pre-treatment of seeds with salicylic acid attenuates cadmium chloride-induced oxidative damages in the seedlings of mungbean (Vigna radiata L. Wilczek)

Abstract

Salicylic acid (SA) is known to be responsive to major abiotic stress factors like drought, cold, heavy metal toxicity, and such other forms of osmotic stress. However, molecular regulation of SA signaling, including the mechanism of action in heavy metal stress tolerance, is not well understood, so that currently there is an increasing trend in studies in this area. The present study was focused to assess the possible regulatory role of SA in mitigating oxidative damages under cadmium (Cd) toxicity, taking mungbean (Vigna radiata) seedlings as the experimental model. Pre-soaking of seeds in SA, prior to Cd exposure of germinated seedlings, alleviated the overall detrimental effects of Cd toxicity. The SA-promoted seedling growth under stress was correlated with improved germination percentage due to enhanced α-amylase activity, thereby stimulating tissue growth, biomass, and relative water content. The seedlings showed considerably less chlorophyll degradation or reduced chlorophyllase activity, lesser malondialdehyde and total peroxide content, and increased reducing power. The loss in free amino acid and cysteine pool, and protease activity with Cd stress was overcome by SA-pre-treatment. The restoration to almost the normal level of osmolytes like total sugar and Pro, antioxidants like ascorbic acid, total phenolics and polyphenol oxidase activity, and antioxidative enzymes like catechol peroxidase, ascorbate peroxidase, catalase and superoxide dismutase, in seedlings grown from SA-pre-treated seeds also pointed towards partial Cd stress recovery. Isozyme profiling revealed induction of isoform(s) of guaiacol peroxidase and superoxide dismutase, in particular, in stressed seedlings, grown from SA-pre-treated seeds. Pre-treatment could also overcome the Cd-induced loss in nitrate reductase activity, leading to better nitrogen assimilation. While the decline in pyruvate dehydrogenase and malate dehydrogenase with Cd stress was recovered by SA, the increased succinate dehydrogenase activity with stress was lowered by SA, since lesser malic acid was required for osmotolerance in presence of SA. On the basis of the above observations, it can be concluded that priming with SA before seed sowing can attenuate Cd-induced oxidative stress in mungbean seedlings through induced antioxidative defense mechanism and improving the overall growth performances.