Soil salinity is one of the major abiotic stress factors that hampers plant growth and productivity by limiting photosynthesis and other related metabolic processes. In this study we investigated whether treatment with proline and/or 24-epibrassinolide (EBL) to two contrasting cultivars of Brassica juncea (L.) Czern and Coss viz. Varuna and RH-30 could counteract with the adverse effects of salinity on photosynthesis and seed yield. Plants were treated with proline and/or 24-epibrassinolide (EBL) at 28 and 29d-stages of growth. Salt stress reduced plant growth, photosynthetic attributes, efficiency of PSII (Fv/Fm), leaf water potential and finally seed yield, at harvest but improved the activity of antioxidant enzymes in both the cultivars in a concentration dependent manner. Exogenous application of EBL with proline completely neutralised the adverse effects of salt at 78 mM or 117 mM stress levels whereas the treatment partially neutralised the impact of highest salt concentration of 156 mM, through the upregulation of the antioxidant system.

The present study was carried out to screen out the best concentration of proline, applied exogenously as foliar spray, which will have beneficial effects on growth and physio-biochemical parameters in two varieties of Brassica juncea (‘Varuna’ and ‘RH-30’). The proline concentrations tested in this experiment were 0, 10, 20 or 30 mM. The foliar spray was done at 29 days after sowing (DAS) and sampling at 60 DAS. Out of these concentrations, 20 mM proline was found best. The proline treatment significantly increased the growth, net photosynthetic rate and related attributes, SPAD value of chlorophyll, leaf carbonic anhydrase activity and quantum yield of photosystem II, as well as proline content and activity of antioxident enzymes also increased in both the varieties at 60 d stage of growth. The result was more pronounced in the ‘Varuna’ than in ‘RH-30’.

The present investigation was conducted to evaluate the silicon (Si) mediated responses in different cultivars of Indian mustard (Brassica juncea) and to evaluate if Si could be used as an essential, beneficial, or quasi-essential element for growth and development of these cultivars. Surface sterilized seeds were sown in pots and allowed to germinate under natural environmental conditions. At 10, 12, 14, 16, and 18 days after germination, a range of Si concentrations (0.0, 0.2, 0.4, 0.8 and 1.6 mM) was administered to the soil and at 30 days post germination the plants were sampled to assess growth and development, leaf gas exchange traits and plant biochemical parameters, including activities of carbonic anhydrase, catalase, peroxidase, superoxide dismutase, and protein and proline content. The results demonstrate a dual response to Si concentration: 0.8 mM of Si significantly increased plant growth and development (length of root and shoot, fresh and dry biomass, and leaf area) and photosynthetic efficiency, and enhanced the antioxidant response in T-59 over all the other cultivars tested, whereas, 1.6 mM of Si significantly reduced the above parameters. It is therefore concluded that low levels of Si could be used as a quasi-essential element for enhanced photosynthetic efficiency and antioxidant response of Brassica juncea plants; however, the response is cultivar specific and concentration dependent.

This study was conducted to provide an insight into the effect of Se (through soil) induced changes in Brassica juncea plants in the presence and absence of 24-epibrassinolide (EBL; foliar). The Se treatments showed dual response, 10 mu M of Se significantly increased growth, water relations, photosynthetic attributes along with carbonic anhydrase activity whereas its higher concentrations proved inhibitory in concentration dependent manner. The follow-up application of EBL to the Se stressed plants improved growth, water relations, photosynthesis and simultaneously enhanced the various antioxidant enzymes viz. catalase, peroxidase and superoxide dismutase with the excess accumulation of proline. In addition to this, 10 mu M Se increases the efficacy of 10(-8) M of EBL and both in combination showed maximum increase for the growth and photosynthetic traits of plants. On the other hand, the elevated level of antioxidant enzymes as well as proline could have conferred tolerance to the Se-stressed plants resulting in improved growth, water relations and photosynthesis. (C) 2015 Elsevier Ltd. All rights reserved.

Excess cadmium accumulation in shoot decreases the photosynthetic attributes and the activity of carbonic anhydrase (CA; E.C. 4.2.1.1) thereby retarding plant growth metabolism, in a cultivar dependent manner. Two mustard (Brassica juncea) varieties were treated with increasing cadmium doses (0, 25, 50 or 100 mg CdCl2 kg−1 of soil) in the soil in a net house. The photosynthetic features, activity of CA, and the yield attributes were recorded in association with morphological characters. A clear-cut difference in these features was noted among the varieties, where Varuna excelled in its resistance to the cadmium toxicity with better growth and yield, at harvest.

The role of 28-homobrassinolide (HBL) in countering nickel-induced oxidative damage through overexpression of antioxidant enzymes and proline in Vigna radiata has been investigated. Two varieties of V. radiata, one sensitive to Ni (PDM-139) and the other tolerant to Ni (T-44), were sown in the soil fed with different levels (0, 50, 100 or 150 mg kg(-1)) of Ni, and at 29-day stage, foliage of plants was applied with deionized water (control), 10(-8) or 10(-6) M of HBL. The plants were sampled at 45-day stage of growth to assess various physiological as well as biochemical characteristics. The remaining plants were allowed to grow up to maturity to study the yield characteristics. The growth traits, leghemoglobin, nitrogen and carbohydrate content in the nodules, leaf chlorophyll content, photosynthesis efficiency, leaf water potential, activities of nitrate reductase, carbonic anhydrase and nitrogenase decreased proportionately with the increasing concentrations of nickel, whereas electrolyte leakage, various antioxidant enzymes viz. catalase, peroxidase and superoxide dismutase and accumulation of proline increased at 45-day stage. However, the exogenously applied HBL to the nickel-stressed or non-stressed plants improved growth, nodulation and photosynthesis and further enhanced the various antioxidant enzymes viz. catalase, peroxidase and superoxide dismutase and accumulation of proline. The deleterious impact of Ni on the plants was concentration dependent where HBL applied to the foliage induced overexpression of antioxidant enzyme and accumulation of proline (osmolyte) which could have conferred tolerance to Ni up to 100 mg kg(-1), resulting in improved growth, nodulation, photosynthesis and yield attributes.

Cadmium, a non-essential and toxic metal, negatively affects plant growth and productivity, and alters the plant's physiological processes necessary for its survival. The present study was designed to explore the individual and combined effects of calcium and salicylic acid (SA) on the morphology and physiology of Brassica juncea L. cv. Varuna under cadmium stress. The application of calcium (2 mM) through the soil and/or SA (10(-5) M) as foliar spray enhanced the growth, photosynthetic parameters, and proline content determined after 45 days of treatment. The application of cadmium (6 mg kg(-1)) through the soil was toxic and decreased both growth and the photosynthetic parameters. The application of calcium and SA in combination was most effective in alleviating the harmful effects of cadmium on growth and photosynthesis. Calcium and SA clearly induced plant protection mechanisms by enhancing proline and chlorophyll accumulation in the leaves.

The aim of this study was to determine the effect of salicylic acid (SA) on nitrogen fixation and assimilation under conditions of cadmium stress in chickpea plants. Chickpea seeds were sown in pots containing 0, 25, 50, or 100 mg of cadmium per kilogram of soil. The foliage of the 30-day-old plants was sprayed with 10(-5) M SA, and the activities of nitrogenase, nitrate reductase, glutamine synthetase, glutamate synthase, and glutamate dehydrogenase were investigated. SA exposure increased the number of nodules, fresh and dry nodule masses, leghemoglobin content, and activity of the nitrogen-fixing enzyme nitrogenase compared with the control conditions. Furthermore, SA application enhanced the activities of the enzymes involved in nitrogen assimilation, in both the control and cadmium-stressed plants. The overall results indicate that SA increases the fixation and assimilation of nitrogen regardless of whether the plants are grown in the presence or absence of cadmium.

The present study was designed with an objective to elucidate the cumulative effect of the exogenous application of 20 mM proline and 10(-5) M of salicylic acid (SA) on the physio-morphological changes in chickpea plants exposed to 0, 25, 50, or 100 mg cadmium (Cd) per kg of soil. The exogenous application of proline and SA alleviated completely the ill effects generated by the presence of metals in soil which was expressed in terms of increased dry matter accumulation and nodulation, enhanced efficiency of nitrogen fixation, and its assimilation. The foliar spray of SA and proline resulted in an increased stomatal conductance and net photosynthetic rate in the Cd-stressed plants. The oxidative stress generated in plants was completely overcome by the combined application of proline (20 mM) and SA (10(-5) M) by increasing the activity of antioxidative enzymes [catalase (CAT), peroxidase (POX) and superoxide dismutase (SOD)] coupled with an increased accumulation of endogenous proline which was found to be maximum in the plants exposed to 100 mg Cd per kg of soil, and also sprayed with proline and SA.

High temperature is a serious threat to crop production. Brassinosteroids (BRs), a group of plant steroidal hormones, can reduce effects of abiotic stresses. The present study was aimed to study the potency of brassinosteroids on high temperature induced changes in Indian mustard (Brassica juncea L.) for effects on growth, chlorophyll, photosynthesis, photosystem II, antioxidant system and proline. Surface sterilized seeds of Indian mustard were sown in pots, grown for 21 days and treated with double distilled water or 0.01 µM of 28-homobrassinolide. Treated plants, after 24 h, were exposed to 30°C or 40°C for 48 h. One set of plants were kept at ambient temperature, 25°C, as the control. Plants were harvested at 30 days stage of growth to assess the various parameters. Plants exposed to 40°C had a decline in growth, leaf water potential, chlorophyll, photosynthetic rate, and activities of carbonic anhydrase (E.C.4.2.1.1) and nitrate reductase (E.C.1.6.1.1). The 28-homobrassinolide alone improved growth and photosynthesis responses along with various enzymes activities. Treatment of plants with HBL prior to exposure to 40°C, partially reduced damage and completely controlled damage when exposure was to 30°C. Levels of the antioxidative enzymes catalase (E.C.1.11.1.6), peroxidase (E.C.1.11.1.7), and superoxide dismutase (E.C.1.15.1.1), and the level of proline increased in response to 30 or 40°C and were further enhanced in the presence of 28-homobrassinolide. Plants grown under high temperature had increased levels of H2O2; application of HBL before temperature treatment decreased H2O2 content compared to the control. Elevated levels of antioxidative enzymes and proline might be responsible for conferring tolerance to high temperature stress in Indian mustard and overcome the loss of productivity of the crop.

The aim was to explore the responses of varied doses of manganese in mustard plants and also to test the proposition that salicylic acid induced up-regulation of antioxidant system which protect photosynthetic apparatus. Seeds were sown in pots and allowed to germinate under natural environmental conditions. At 10 days stage, soils in the pots were enriched with different levels (0, 3, 6, or 9 mM) of Mn for three days and allowed to grow till 30 day stage. At 31st day, foliage of plants was sprayed with 10 μM of salicylic acid (SA) and then allowed to grow till 45 days. Then plants were harvested to assess various growth, leaf gas exchange traits and biochemical parameters. Mn-treated plants had diminished growth, water relations and photosynthetic attributes along with carbonic anhydrase activity whereas; the level of lipid peroxidation, electrolyte leakage, accumulation of H2O2 along with proline accumulation and antioxidant enzymes increased in a concentration dependent manner. Follow-up application of SA to the Mn-stressed plants improved growth, water relations and photosynthetic traits, accelerated the activity of antioxidant enzymes and also the accumulation of proline. SA mediated tolerance to Mn-stressed plants could have due to up-regulation of antioxidant enzymes and proline accumulation.

Low temperature can delay growth and development, reduce productivity, or cause plant death. An experiment was carried out to determine the most sensitive and most tolerant tomato (Solanum lycopersicum L.; variety S-22, Selection N-5, Pusa Gorav, K-21, Pusa Ruby, Hera Research, and PKM-1) to low temperature. Forty-day-old seedlings were exposed to day/night temperatures of 10/3°C, 12/7°C, 20/14°C, or 25/18°C (control) for 24 h in a plant growth chamber and then transferred to ambient environmental conditions in a net house and maintained for 60 days. Decreasing temperature led to decreases in growth, chlorophyll content, and photosynthesis rate in all varieties. Activity of antioxidant enzymes catalase, peroxidase, and superoxide dismutase and proline accumulation in leaves increased in all varieties as temperature decreased. Variety S-22 had the most antioxidant enzyme activity and proline accumulation and ‘PKM-1’ had the lowest antioxidant enzyme activity and proline content; these were classified as tolerant and sensitive, respectively. Tolerant tomato varieties provide options for producers where low temperature can interfere with plant development.

Increasing contamination and higher enrichment ratio of non-essential heavy metal cadmium (Cd) induce various toxic responses in plants when accumulated above the threshold level. These effects and growth responses are genotype and Cd level dependent. An experiment was conducted to analyze the effect of Cd toxicity in Brassica juncea [L] Czern and Coss by selecting its two varieties Varuna and RH-30. Cadmium (0, 25, 50 or 100 mg CdCl2 kg(-1) of soil) fed to soil decreased the values of growth characteristics, activity of nitrate reductase and leaf water potential, whereas activities of antioxidant enzymes and proline content increased with the increasing concentration of Cd, observed at 30 and 60 day stages of growth, in both the varieties. Moreover, Cd uptake by the roots was higher in RH-30 than Varuna. Also the activity of antioxidant enzymes and proline accumulation were higher in Varuna with increasing soil level of Cd. Out of the two varieties, Varuna was more tolerant than RH-30 to Cd stress. (C) 2013 Production and hosting by Elsevier B.V. on behalf of King Saud University.

Salicylic acid (SA) and its derivatives are the most widely known drugs in the world used to reduce pain and fever, helping to treat many inflammatory diseases, in the prevention of coronary heart disease and heart attacks, and in tumor suppression. This substance is also characterized by a high metabolic and physiological activity, which enables it to perform regulatory functions in plant development and reaction to biotic and abiotic stress factors. Under non-stress conditions, SA is present in plant tissues in quantities of several mg to several ng in one g of fresh mass. Its level substantially increases in plants exposed to water deficit. The accumulation of SA may result from its de novo synthesis through activation of enzymes involved in the synthesis of SA from phenylalanine, i.e. phenylalanine ammonia lyase (PAL) and benzoic-acid-2-hydroxylase (BA2H). SA accumulated in plants growing under the conditions of water shortage may be involved in the regulation of mechanisms responsible for resistance to drought through the control of water balance and activation of antioxidant system. Large body of evidences revealed that exogenous application of SA was effective in modeling plant responses to water deficit. Plant pre-treatment with SA resulted in higher tissue water content, increased activity of antioxidant enzymes, decreased level of lipid peroxidation and membrane injury and it also protected nitrate reductase activity against inhibition under water deficit conditions. These changes enable plants to survive under drought and play an essential role in countering the adverse effects of stress on growth and yield.

Tomato (Solanum lycopersicum L.) is moderately salt sensitive and yield can be reduced by 50% when exposed to a 7.5 dS·m−1 electrical conductivity (EC) saline solution. The response of tomato, cv. K-21, to presowing seed treatment with sodium chloride (NaCl) and sodium nitroprusside (SNP) was investigated. Before sowing, surface-sterilized seed of tomato were soaked in 50, 100, or 150 mM NaCl for 8 h and then transferred to a 10−5 M solution of SNP for 8 h. Plants were sampled at 45 and 60 days after sowing (DAS) to assess carbonic anhydrase activity (E.C. 4.2.1.1), relative water content, photosynthetic attributes, and growth parameters. Activity of carbonic anhydrase and all other parameters was increased by SNP application following the NaCl treatment. Detrimental effects generated by the 50 mM NaCl concentration were completely neutralized by SNP at 60 DAS, whereas those of highest NaCl concentration were not reversed by SNP at both sampling stages. It appears that SNP alleviates salinity stress up to 50 mM NaCl.

Among the compatible solutes, glycine betaine (GB) is particularly an effective osmolyte against abiotic stress. Metabolic acclimation of GB is regarded as a basic strategy for the protection and survival of plants in harsh environmental conditions. Plant species vary in their capacity to synthesize GB. Some plants, such as spinach and barley, accumulate relatively higher levels of GB in their chloroplasts while others, like Arabidopsis and tobacco, lack this compound. The accumulation of GB is induced under stress conditions and the level of GB is correlated with the degree of tolerance to stress. Genetic engineering has allowed the introduction of genes of its biosynthetic pathway into GB-deficient species from both microorganisms and higher plants. This approach has facilitated investigation of the importance of GB in stress protection. However, the level of GB in transgenic plants is relatively low. An alternative approach of exogenous application of GB to plants under stress has gained some attention. In this review, the protective role of GB in conferring tolerance to plants against various abiotic stresses through both exogenous application and genetic engineering has been summarized. _____________________________________________________________________________________________________________

This study examines the impact of 28-homobrassinolide (HBL) in alleviating the effects of cadmium (Cd) and salinity (NaCl) on wheat plants solely and against the synergy. The surface sterilized seeds of Triticum aestivum cv. PBW-373 were sown in the soil amended either with salinity or cadmium or both. The foliage in was sprayed at 20d after sowing (DAS) both in stressed and non-stressed plants. The spray of HBL at 20 DAS increased almost all the parameters while decreased the H2O2 content and lipid peroxidation in the leaves. The presence of cadmium and/or salinity decreased the values for all the growth and photosynthetic parameters but improved the activity of antioxidant enzymes and proline content in 30d old plants. However, the ill effects observed under NaCl and/or Cd treatment were completely overcomed by the spray of HBL to the plants at 20d stage. The spray of HBL to stressed plants further increased the antioxidant enzyme activities and proline content thereby giving tolerance to the plants against the stress.

Salt stress is among the major abiotic stresses that adversely affect the global crop production and its adverse impacts are getting more serious in the regions where saline water is used for irrigation. It induces reactive oxygen species, alters the activity of antioxidant system and adversely affects the process of photosynthesis. Various strategies have been employed to mitigate the deleterious effects of salt stress. Presently, the recommended strategies to overcome the adverse effects of salt stress include the use of tolerant cultivars, ameliorative water management and diverse cultural practices. However, none of these approaches have been found to be fully effective under salt stress conditions. An alternative and technically simpler approach to induce salt stress tolerance is the exogenous application of plant growth regulators (PGRs). This technique has gained significant importance during the past decade. PGRs have been implicated to regulate a wide range of metabolic and physiological activities in plants, ranging from cell division and organogenesis to protection against biotic and abiotic stresses. One of the important factors for enhanced plant productivity by PGRs is their efficiency to overcome the salt-induced stress conditions. Recent findings on the effects of brassinosteroids and polyamines on the salt stress tolerance of crops open new avenues to address the salinity problems. This review enlightens the role of brassinosteroids and polyamines in different plant processes like their role in regulation of photosynthesis, antioxidant systems and other related aspects, thereby improving overall performance of plants.