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Sulphur(S)-deficiency is emerging as a major problem for agricultural productivity. Cadmium (Cd) exerts its phytotoxicity against defence, growth and development. S-rich compounds (glutathione, phytochelatins, etc.) limit the impacts of Cd-toxicity. We investigated what happens during S-deficiency and Cd exposure (dual stress) in mustard. Major findings were: S-deficiency increases the susceptibility of plants to Cd-generated oxidative damage and modulates the AsA-GSH antioxidant cycle; SOD is not the first line of defence against metal stress and S-rich metabolites play a prime role; S-deprived plants are more prone to Cd and oxidative stress; and great loss is incurred to defence modules and growth under dual stress, restricting the efficiency of phytoremediation.

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Parthenium hysterophorus is a plant that tolerates drought and salinity to an extremely high degree. Higher expression of stress-responsive proteome contributes for greater defence against abiotic stresses. Thus, P. hysterophorus could be a rich source of genes that encode stress-imparting mechanisms and systems. The present study utilizes comparative physiological and proteomic approaches for identification of key proteins involved in stress-defence of P. hysterophorus. Thirty-days-old plants were exposed to drought (10% PEG 6000) and salinity (160 mM NaCl) for 10 days duration. Both stresses induced oxidative stress estimated in terms of TBARS and H2O2. Levels of both enzymatic and non-enzymatic antioxidants were elevated, more by drought than salinity. Particularly, SOD, GR, CAT and GST proved to be assisting as very commendable defence under drought, as well as salinity. Levels of ascorbate, glutathione and proline were also increased by both stresses, more in response to drought. Comparative proteomics analysis revealed a significant change in relative abundance of 72 proteins under drought and salinity. Drought and salinity increased abundance of 45 and 41 proteins and decreased abundance of 24 and 26 proteins, respectively. Drought and salinity increased and decreased abundance of 31 and 18 proteins, respectively. The functions of identified proteins included those related to defence response (26%), signal transduction (13%), transcription and translation (10%), growth and development (8.5%), photosynthesis (8.5%), metabolism (7%), terpenoid biosynthesis (5.5%), protein modification and transport (7%), oxido-reductase (4%) and Miscellaneous (11%). Among the defence related proteins, antioxidants and HSPs constituted 26% and 21%, respectively. Present study suggests a potential role of defence proteins. Proteins involved in molecular stabilization, formation of osmolytes and wax and contributing to stress-avoiding anatomical features emerged as key and complex mechanisms for imparting stress tolerance to P. hysterophorus.

BackgroundLead (Pb) and mercury (Hg) are persistent hazardous metals in industrially polluted soils which can be toxic in low quantities. Metal toxicity can cause changes at cellular and molecular level which should be studied for better understanding of tolerance mechanism in plants. Soybean (Glycine max L.) is an important oilseed crop of the world including India. Indian soils growing soybean are often contaminated by Pb and Hg. The aim of this study was to explore how soybean root nodule responds to Pb and Hg through proteomic and ecophysiological alterations in order to enhance tolerance to metal stress.ResultsSoybean plants were exposed to Pb (30 ppm PbCl2) and Hg (0.5 ppm HgCl2) to study histological, histochemical, biochemical and molecular response of N2-fixing symbiotic nodules. Both Pb and Hg treatment increased the level of oxidative stress in leaves and nodules. Chlorosis in leaves and morphological/anatomical changes in nodules were observed. Activities of ascorbate peroxidase, glutathione reductase and catalase were also modulated. Significant changes were observed in abundance of 76 proteins by Pb and Hg. Pb and Hg influenced abundance of 33 proteins (17 up and 16 down) and 43 proteins (33 up and 10 down), respectively. MS/MS ion search identified 55 proteins which were functionally associated with numerous cellular functions. Six crucial proteins namely catalase (CAT), allene oxide synthase (AOS), glutathione S-transferase (GST), calcineurin B like (CBL), calmodulin like (CML) and rapid alkalinisation factor (RAF) were selected for transcript abundance estimation. The qRT-PCR based real time expression exhibited a positive correlation with proteomics expression except for GST and RAF.ConclusionSoybean root nodule responds to metal stress by increased abundance of defence, development and repair related proteins. An efficient proteomic modulation might lead to metal-induced stress tolerance in N2-fixing nodules. Although concentrations of Pb and Hg used in the study cannot be considered equimolar, yet Hg seems to induce more changes in nodule proteomic profile, and higher damage to both bacteroides and root anatomy.Electronic supplementary materialThe online version of this article (10.1186/s12870-018-1499-7) contains supplementary material, which is available to authorized users.

Parthenium hysterophorus is a weed of global concern with high threshold of tolerance against most of biotic and abiotic stresses. Phytochemical profile and in vitro antioxidant analysis may help in understanding its tolerance to stresses. Root, stem, leaf, phyllary, and receptacle (including disc and ray florets) were chemotyped employing GC tof-MS and assessed for antioxidant activity by DPPH, FRAP, HRSA, and TAC assays. Phytochemicals identified were terpenes, fatty acids, hydrocarbons, phytosterols, and compounds of miscellaneous chemical nature. Organ-specific maximum concentration of metabolite was β-vatirenene (root), hexadecanoic acid methylester (stem), aristolene epoxide (leaf), hexadecanoic acid methylester (phyllary), and hexadecanoic acid methylester (receptacle). Identified metabolites could be associated with stress tolerance mechanisms, basic metabolism, and allelopathy, etc. Root extracts showed highest antioxidant potential followed by receptacle. It can be concluded that diverse and unique phytochemical profile and great antioxidant potential make P. hysterophorus stress-tolerant, hence a weed of global habitat.

Sulphur (S) deficiency, cadmium (Cd) toxicity and their combinations are of wide occurrence throughout agricultural lands. We assessed the impact of short-term (2 days) and long-term (4 days) applications of cadmium (40 μg/g soil) on spinach plants grown on sulphur-sufficient (300 μM SO) and sulphur-deficient (30 μM SO) soils. Compared with the control (+S and -Cd), oxidative stress was increased by S deficiency (-S and -Cd), cadmium (+S and +Cd) and their combination stress (-S and +Cd) in the order of (S deficiency) < (Cd stress) < (S deficiency and +Cd stress). SDS-PAGE profile of leaf proteins showed a high vulnerability of rubisco large subunit (RbcL) to S deficiency. Rubisco small subunit (RbcS) was particularly sensitive to Cd as well as dual stress (+Cd and -S) but increased with Cd in the presence of S. Cysteine content in low molecular weight proteins/peptide was also affected, showing a significant increase under cadmium treatment. Components of ascorbate-glutathione antioxidant system altered their levels, showing the maximum decline in ascorbate (ASA), dehydroascorbate (DHA), total ascorbate (ASA + DHA, hereafter TA), glutathione (GSH) and total glutathione (GSH + GSSG, hereafter TG) under S deficiency. However, total ascorbate and total glutathione increased, besides a marginal increase in their reduced and oxidized forms, when Cd was applied in the presence of sufficient S. Sulphur supply also helped in increasing the activity of superoxide dismutase (SOD), ascorbate peroxidase (APX), glutathione reductase (GR) and catalase (CAT) under Cd stress. However, their activity suffered by S deficiency and by Cd stress during S deficiency. Each stress declined the contents of soluble protein and photosynthetic pigments; the highest decline in contents of protein and pigments occurred under S deficiency and dual stress respectively. The fresh and dry weights, although affected adversely by every stress, declined most under dual stress. It may be concluded that an optimal level of S is required during Cd stress for better response of SOD, APX, GR and CAT activity, as well as synthesis of cysteine. RbcS is as highly sensitive to S deficiency as RbcL is to Cd stress.