Tomato (Solanum lycopersicum L.) being a widespread and most commonly consumed vegetable all over the world has an important economic value for its producers and related food industries. It is a serious matter of concern as its production is affected by arsenic present in soil. So, the present study, investigated the toxicity of As(V) on photosynthetic performance along with nitrogen metabolism and its alleviation by exogenous application of nitrate. Plants were grown under natural conditions using soil spiked with 25 mg and 20 mM, As(V) and nitrate, respectively. Our results revealed that plant growth indices, photosynthetic pigments, and other major photosynthetic parameters like net photosynthetic rate and maximum quantum efficiency (F v /F m ) of photosystem II (PSII) were significantly (P B 0.05) reduced under As(V) stress. However, nitrate application significantly (P B 0.05) alleviated As(V) toxicity by improving the aforesaid plant responses and also restored the abnormal shape of guard cells. Nitrogen metabolism was assessed by studying the key nitrogen-metabolic enzymes. Exogenous nitrate revamped nitrogen metabolism through a major impact on activities of NR, NiR, GS and GOGAT enzymes and also enhanced the total nitrogen and NO content while malondialdehyde content, and membrane electrolytic leakage were remarkably reduced. Our study suggested that exogenous nitrate application could be considered as a cost effective approach in ameliorating As(V) toxicity.

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.

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The accumulation and toxicity of chromium (Cr) in Indian mustard (Brassica juncea L.) under ethylene diamine tetraacetic acid (EDTA) and oxalic acid (OA) as chelating agents was studied. Plants were exposed to Cr(VI) and chelating agents in four experimental set-ups as Cr(VI), Cr(VI) + EDTA (1 : 1), Cr(VI) + OA (1 : 1) and Cr(VI) + EDTA + OA (1 : 1 : 1), where each set-up comprised of 0, 6.25, 12.5 and 25.0 mg of Cr(VI) and/or chelating agents in 250 g of soil. Results conferred that EDTA augmented bio-concentration factor in all the three doses of Cr(VI), OA considerably increased translocation factor in all the treatments, including control, and the combined application of the two chelates escalated both the aforesaid factors. Moreover, these chelating agents help in ameliorating Cr(VI) toxicity asserted by low degree of lipid peroxidation, insubstantial damage in root and shoot length, fresh and dry biomass, chlorophyll and leaf gas exchange parameters. Besides, plants showed a robust detoxification mechanism primarily by significant (P < 0.05) production of reduced glutathione and phytochelatins among other enzymatic and nonenzymatic antioxidants under these chelating agents. The present findings suggest that Indian mustard could be used as a potential phytoremediator of Cr(VI) under the combined application of EDTA and OA.

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Heavy metals affect plant system in various toxic ways including morphophysiological alterations and genotoxic damages inside a plant cell. The extent of DNA damage under any genotoxic agents can be effectively measured in single cells applying comet assay approach. Comet assay primarily measures DNA strand breakage in single cells and its use has increased in different areas: clinical applications, human monitoring, radiation biology and genetic ecotoxicology. This paper is a review of the detailed protocol and precautions to be taken while performing comet assay and may have been slightly modified from other original protocols according to the plant, organ, cell type, etc. In conclusion, the study reviewed in this paper demonstrate that the comet assay application in plants provides a reliable, sensitive and rapid system for the study of environmental genotoxicity caused by heavy metals.