Counteractive mechanism (s) of salicylic acid in response to lead toxicity in Brassica juncea (L.) Czern. cv. Varuna

Abstract

Salicylic acid alleviates lead toxicity in Brassica juncea (L.) by promoting growth under non-stress and activating stress-defense mechanism (s) under lead stress conditions. It also boosts the ascorbate-glutathione cycle and thus helps in minimizing oxidative and DNA damage. Brassica juncea plants were exposed to different concentrations (0, 500, 1000 and 2000 mg kg) of lead (Pb) and subsequently sprayed with 0.5 mM of salicylic acid (SA) to check for morphological and leaf gas exchange parameters like transpiration rate (E), stomatal conductance (GHO), net photosynthetic rate (A) and maximum quantum yield of PS II (F/F). Leaf epidermis by scanning electron microscopy (SEM), enzymatic and non-enzymatic components of ascorbate-glutathione (AsA-GSH) cycle, DNA damage by comet assay, lipid peroxidation and endogenous SA quantification by HPLC were analyzed. Lead accumulation in root, shoot and its sub-cellular distribution ratio (SDR) and localization was also determined using atomic absorption spectroscopy (AAS) and rhodizonate-dye staining method, respectively. Results revealed that notable amount of Pb was accumulated in root and shoot in dose-dependent manner which significantly (P ≤ 0.05) posed the toxicity on the majority of morphological parameters, structural integrity of epidermal and guard cells, photosynthetic pigments, malondialdehyde (MDA) and HO content. Notable decrease in leaf gas exchange parameters, F/F, poor performance of AsA-GSH cycle and striking amount of DNA damage, was found as well. However, SA revoked Pb toxicity to a great extent by promoting growth, chlorophyll content, improving the A, F/F, boosting the overall performance of AsA-GSH cycle and by lessening the DNA damage.

Salicylic acid‐induced hydrogen sulphide improves lead stress tolerance in pepper plants by upraising the ascorbate‐glutathione cycle

“…In this experiment, the increased accumulation of H 2 O 2 in Pb‐S plants may have been due to an elevation of APX and GR activities. The addition of SA or SA + NaHS further elevated the activity of APX and GR, similarly to what observed in Brassica juncea L. by Agnihotri et al (2018) who reported that SA reduced the activity of APX in Pb‐stressed plants.…”

“…The addition of SA or SA + NaHS resulted in higher activities of DHAR and MDHAR in the Pb‐S pepper plants. The positive effect of SA on DHAR in Brassica juncea L. has been reported by Agnihotri et al (2018). Similar effects of SA on DHAR and MDHAR activities under other stressors has been reported, e.g.…”

“…DHAR and MDHAR are other enzymes allied to the AsA‐GSH cycle: DHAR contributes to the exchange of DHA to AsA, and MDHAR contributes to sustaining the reduced pool of AsA and ascorbate redox status (Sakhno et al 2019). The Pb‐S pepper plants exhibited a decrease in the activities of DHAR and MDHAR, although contradictory results have been reported in Brassica juncea L. (Agnihotri et al 2018).…”

“…Plants have evolved antioxidant defence systems to overcome Pb stress (Halim and Phang 2017), e.g. regulation of the AsA‐GSH cycle‐related enzymes (Agnihotri et al 2018). However, antioxidant defence mechanisms are complex and controlled by numerous factors especially in plants sensitive to Pb stress (Kaya et al 2019).…”

Exogenous salicylic acid alleviates the oxidative damageof Arabidopsis thaliana by enhancing antioxidant defense systemsunder high light

“…A previous study showed that SA increases the content of AsA and GSH in salt-stressed wheat seedlings, which is associated with SA-induced salt tolerance (Wei 2013). Agnihotri et al (2018) also indicated that SA boosts the ascorbate-glutathione cycle and thus helps to alleviate oxidative damage and damage to DNA under lead stress. Consistently, our results show that the SA-treated plants accumulated high concentrations of AsA and GSH, and low concentrations of DHA and GSSG under the high light suggesting that SA could improve the tolerance to high light by regulating the ascorbateglutathione cycle.…”