The effect of sulphur supplementation on cadmium phytotoxicity in wheat and lettuce: changes in physiochemical properties of roots and accumulation of phytochelatins.

Intensive sulphur fertilisation has been reported to improve the nutrient balance and growth of Cd-exposed plants, but the reasons of this phenomenon and the role of sulphur compounds in the resistance to cadmium are unclear. We investigated sulphur supplementation-induced changes in the surface properties of roots and the level of thiol peptides (PCs) in Cd-stressed Triticum aestivum L. (monocots clade) and Lactuca sativa L. (dicots clade) grown in nutrient solution. The combination of three sulphur (2 mM S-basic level, 6 or 9 mM S-elevated levels) and four cadmium (0, 0.0002, 0.02 or 0.04 mM Cd) concentrations was used. The physicochemical parameters of the roots were determined based on the apparent surface area (Sr), total variable surface charge (Q), cation exchange capacity (CEC) and surface charge density (SCD). In Cd-exposed plants supplied with sulphur, a different character and trend in the physicochemical changes (adsorption and ion exchange) of roots were noted. At the increased sulphur levels, as a rule, the Sr, CEC, Q and SCD values clearly increased in the lettuce but decreased in the wheat in the entire range of the Cd concentrations, except the enhanced Sr of wheat supplied with 6 mM S together with elevated (0.0002 mM) and unchanged (0.02, 0.04 mM Cd) value of this parameter at 9 mM S. This indicates a clade-specific and/or species-specific plant reaction. The 6 mM S appears to be more effective than 9 mM S in alleviation of the cadmium's toxic effects on roots. It was found that at 0.02 and 0.04 mM Cd, the use of 6 mM S limits the Cd accumulation in the roots of both species in comparison with the basic S fertilisation. Moreover, PC accumulation was much more efficient in wheat than in lettuce, and intensive sulphur nutrition generally induced biosynthesis of these chelating compounds. Physicochemical parameters together with quantitative and qualitative assessment of thiol peptides can be important indicators of the efficiency of root system functioning under cadmium stress. The differences between the species and the multidirectional character of the changes are a result of the involvement of a number of multi-level mechanisms engaged in the defence against metal toxicity.

Effect of Different Rootstocks on the Salt Stress Tolerance and Fruit Quality of Grafted Eggplants (Solanum melongena L.).

Vegetable grafting is considered a rapid, non-chemical alternative method to relatively slow and expensive breeding to overcome the adverse effect of salinity. Therefore, a soilless experiment was performed to determine the salinity tolerance of eggplant (Solanum melongena) cv. Madonna grafted onto two different rootstocks, Solanum grandifolium × Solanum melongena (SH) and Solanum torvum (ST), as well as self-grafted (SG) and self-rooted (SR) as controls. All groups of plants were treated with 0 mM NaCl or 80 mM NaCl. A significant decrease in the relative leaf chlorophyll content (SPAD value) and chlorophyll concentrations were found in response to NaCl. However, the grafted plants had a higher photosynthetic pigment level than the non-grafted plants grown under saline conditions. Grafting eggplants onto SH significantly enhanced the total fruit yield as compared to the self-rooted plants exposed to salinity by increasing the average fruit weight. Moreover, salt stress significantly increased the whitening index and oxidation potential of fruits. The plants grafted onto SH or ST accumulated more Na+ in their roots than in their fruit or leaves, thus the Na+ partitioning between the above-ground and root parts most probably determines the increased salinity tolerance of the grafted ST and SH plants. To conclude, both the SH and ST rootstocks protected the scions against salinity; the scion showed both increased photosynthetic pigment concentration and chlorophyll fluorescence parameters as well as a lower Na+ concentration under stress that resulted in a higher fruit yield and quality.

Comparative Effects of Two Forms of Chitosan on Selected Phytochemical Properties of Plectranthus amboinicus (Lour.).

In response to stress factors, plants produce a wide range of biologically active substances, from a group of secondary metabolites, which are applied in medicine and health prophylaxis. Chitosan is a well-known elicitor affecting secondary metabolism in plants, but its effect on the phytochemical profile of Plectranthus amboinicus has not been assessed yet. In the present experiment, the effectiveness of the foliar application of two forms of chitosan (chitosan suspension or chitosan lactate) was compared in order to evaluate their potential to induce the accumulation of selected polyphenolic compounds in the aboveground parts of P. amboinicus. It was shown that chitosan lactate had substantially higher elicitation efficiency, as the use of this form exerted a beneficial effect on the analysed quality parameters of the raw material, especially the content of selected polyphenolic compounds (total content of polyphenols, flavonols, anthocyanins, and caffeic acid derivatives) and the free radical-scavenging activity of extracts from elicited plants. Concurrently, it had no phytotoxic effects. Hence, chitosan lactate-based elicitation can be an effective method for optimisation of the production of high-quality P. amboinicus raw material characterised by an increased concentration of health-promoting and antioxidant compounds.

Plant Growth Regulators Improve Grain Production and Water Use Efficiency of Foeniculum vulgare Mill. under Water Stress.

The development of methods increasing plant water use efficiency (WUE) would enhance the ability to grow wild aromatic and medicinally important species. The aim of this research was to determine the effect of plant growth regulators (PGRs) applied by spraying on stress resistance and WUE of fennel subjected to water stress. Plants in the generative stage were more drought tolerant than those in the vegetative stage. Water stress at vegetative stage decreased plant biomass and grain yield by 60% and 61%, respectively. Severe water stress in vegetative stage reduced grain production by 56%, and grains had 43% lower mass than those from non-stressed plants. Application of PGRs at both stages of growth increased grain yield and biomass, but the magnitude of increase depended on the type and application time of PGRs. Plants grown in well-watered conditions and sprayed with methyl jasmonate during the vegetative stage had the highest grain production (2.7 g plant-1), whereas under moderate water stress, plants yielded the best (2.1 g plant-1) when sprayed with epibrassinolide. The maximum WUE for grain (0.91 g L-1) and essential oil production (20 mg L-1) was noted in plants exposed to moderate stress and treated with methyl jasmonate during the vegetative stage.

Protective, Biostimulating, and Eliciting Effects of Chitosan and Its Derivatives on Crop Plants.

Chitosan is a biodegradable and biocompatible polysaccharide obtained by partial deacetylation of chitin. This polymer has been gaining increasing popularity due to its natural origin, favorable physicochemical properties, and multidirectional bioactivity. In agriculture, the greatest hopes are raised by the possibility of using chitosan as a biostimulant, a plant protection product, an elicitor, or an agent to increase the storage stability of plant raw materials. The most important properties of chitosan include induction of plant defense mechanisms and regulation of metabolic processes. Additionally, it has antifungal, antibacterial, antiviral, and antioxidant activity. The effectiveness of chitosan interactions is determined by its origin, deacetylation degree and acetylation pattern, molecular weight, type of chemical modifications, pH, concentration, and solubility. There is a need to conduct research on alternative sources of chitosan, extraction methods, optimization of physicochemical properties, and commercial implementation of scientific progress outcomes in this field. Moreover, studies are necessary to assess the bioactivity and toxicity of chitosan nanoparticles and chitosan conjugates with other substances and to evaluate the consequences of the large-scale use thereof. This review presents the unique properties of chitosan and its derivatives that have the greatest importance for plant production and yield quality as well as the benefits and limitations of their application.

NaCl-Induced Elicitation Alters Physiology and Increases Accumulation of Phenolic Compounds in Melissa officinalis L.

In nature, plants usually produce secondary metabolites as a defense mechanism against environmental stresses. Different stresses determine the chemical diversity of plant-specialized metabolism products. In this study, we applied an abiotic elicitor, i.e., NaCl, to enhance the biosynthesis and accumulation of phenolic secondary metabolites in Melissa officinalis L. Plants were subjected to salt stress treatment by application of NaCl solutions (0, 50, or 100 mM) to the pots. Generally, the NaCl treatments were found to inhibit the growth of plants, simultaneously enhancing the accumulation of phenolic compounds (total phenolics, soluble flavonols, anthocyanins, phenolic acids), especially at 100 mM NaCl. However, the salt stress did not disturb the accumulation of photosynthetic pigments and proper functioning of the PS II photosystem. Therefore, the proposed method of elicitation represents a convenient alternative to cell suspension or hydroponic techniques as it is easier and cheaper with simple application in lemon balm pot cultivation. The improvement of lemon balm quality by NaCl elicitation can potentially increase the level of health-promoting phytochemicals and the bioactivity of low-processed herbal products.

High Temperature Alters Secondary Metabolites and Photosynthetic Efficiency in Heracleum sosnowskyi.

Due to global warming, invasive species have spread across the world. We therefore studied the impact of short-term (1 day or 2 days) and longer (7 days) heat stress on photosynthesis and secondary metabolites in Heracleum sosnowskyi, one of the important invasive species in the European Union. H. sosnowskyi leaves exposed to short-term heat stress (35 °C/1 d) showed a decrease in chlorophyll and maximum potential quantum efficiency of photosystem II (Fv/Fm) compared to control, 35 °C/2 d, or 30 °C/7 d treatments. In turn, the high level of lipid peroxidation and increased H2O2 accumulation indicated that the 30 °C/7 d stress induced oxidative damage. The contents of xanthotoxin and bergapten were elevated in the 2 d and 7 d treatments, while isopimpinellin was detected only in the heat-stressed plants. Additionally, the levels of free proline and anthocyanins significantly increased in response to high temperature, with a substantially higher increase in the 7 d (30 °C) treatment. The results indicate that the accumulation of proline, anthocyanins, and furanocoumarins, but not of phenolic acids or flavonols, contributes to protection of H. sosnowskyi plants against heat stress. Further studies could focus on the suppression of these metabolites to suppress the spread of this invasive species.

Eliciting effect of foliar application of chitosan lactate on the phytochemical properties of Ocimum basilicum L. and Melissa officinalis L.

An increase in the content of secondary metabolites in herbal plants is desirable due to their therapeutic and nutraceutical properties. Therefore, the effects of foliar spray of 100 mg/L or 500 mg/L of chitosan lactate (ChL) on the accumulation of selected phenolics and physiological parameters of basil and lemon balm were investigated. In basil, the concentration of rosmarinic acid (RA) increased after application of 100 mg/L of ChL. In turn, in lemon balm both ChL concentrations increased the accumulation of RA and anthocyanins, while the level of total phenolic compounds (TPC) was elevated only at the dose of 100 mg/L of ChL. Elicitation of basil with 500 mg/L of ChL increased the shoot biomass. Therefore, such an elicitor as ChL can enhance the accumulation of valuable phytochemicals in Lamiaceae species. This simple and non-laborious method can be used for elicitation of herbal plants in production of functional food.

Organic nitrogen modulates not only cadmium toxicity but also microbial activity in plants.

It is known that organic nitrogen may modify uptake and toxicity of metals but direct metabolic and microbial comparison of various organic N sources is not available. We therefore studied comparative impact of additional N sources (nitrate, urea or allantoin as 1 mM of N for each compound in addition to 15 mM of inorganic N in the Hoagland solution) on Cd toxicity and microbial activity in common crop cucumber. Organic N significantly elevated the growth, chlorophyll content and photosynthetic activity under Cd excess in comparison with inorganic N though the impact on Cd uptake was negligible. Both organic N compounds also affected accumulation of mineral nutrients, total N, amino acids, and protein content in Cd-stressed plants. Among organic acids, mainly allantoin and partially urea affected accumulation of citrate and tartrate. The most notably, we detected that allantoin was decomposed even within 24 h by microbes into the urea, but it significantly elevated rhizosphere microbial activity. All these data indicate that allantoin is metabolized by plants/microbes into the urea and that it affects microbes mainly in the rhizosphere, which could contribute to amelioration of Cd toxicity.

Difference between Selenite and Selenate in the Regulation of Growth and Physiological Parameters of Nickel-Exposed Lettuce.

Nickel is an essential plant micronutrient; however, even at low concentrations, it may be phytotoxic. Selenium is a beneficial element with an alleviating effect that has been confirmed in the case of many abiotic stresses, including metal toxicity. The aim of this study is to assess the effect of two forms of Se (Se(IV) or Se(VI)) on the phytotoxicity, accumulation, and translocation of Ni in lettuce. Nickel causes a reduction in lettuce growth and vitality of roots, probably through increased lipid peroxidation. The application of Se(IV) to a Ni-contaminated medium resulted in a further reduction of growth, especially in the presence of 6 µM Se(IV). The growth-promoting effect of Se was found only in the 2 µM Se(VI)/10 µM Ni treatment. The application of 6 µM Se, regardless of the Se form, to the Ni-containing substrate caused an increase in shoot Ni concentration. In turn, a decrease in root Ni content was found for all Se treatments. The strong aggravation of Ni phytotoxicity in the presence of 6 µM Se(IV) was most likely related to the accumulation of high Se concentration in the roots, and the combination of high root Ni accumulation caused irreversible dysregulation of cell metabolism.

Selenium Toxicity in Plants and Environment: Biogeochemistry and Remediation Possibilities.

Selenium (Se) is a widely distributed trace element with dual (beneficial or toxic) effects for humans, animals, and plants. The availability of Se in the soil is reliant on the structure of the parental material and the procedures succeeding to soil formation. Anthropogenic activities affect the content of Se in the environment. Although plants are the core source of Se in animal and human diet, the role of Se in plants is still debatable. A low concentration of Se can be beneficial for plant growth, development, and ecophysiology both under optimum and unfavorable environmental conditions. However, excess Se results in toxic effects, especially in Se sensitive plants, due to changing structure and function of proteins and induce oxidative/nitrosative stress, which disrupts several metabolic processes. Contrary, Se hyperaccumulators absorb and tolerate exceedingly large amounts of Se, could be potentially used to remediate, i.e., remove, transfer, stabilize, and/or detoxify Se-contaminants in the soil and groundwater. Thereby, Se-hyperaccumulators can play a dynamic role in overcoming global problem Se-inadequacy and toxicity. However, the knowledge of Se uptake and metabolism is essential for the effective phytoremediation to remove this element. Moreover, selecting the most efficient species accumulating Se is crucial for successful phytoremediation of a particular Se-contaminated area. This review emphasizes Se toxicity in plants and the environment with regards to Se biogeochemistry and phytoremediation aspects. This review follows a critical approach and stimulates thought for future research avenues.

Tolerance of Facultative Metallophyte Carlina acaulis to Cadmium Relies on Chelating and Antioxidative Metabolites.

The impact of long-term chronic cadmium stress (ChS, 0.1 µM Cd, 85 days) or short-term acute cadmium stress (AS, 10 µM Cd, 4 days) on Carlina acaulis (Asteraceae) metabolites was compared to identify specific traits. The content of Cd was higher under AS in all organs in comparison with ChS (130 vs. 16 µg·g-1 DW, 7.9 vs. 3.2 µg·g-1 DW, and 11.5 vs. 2.4 µg·g-1 DW in roots, leaves, and trichomes, respectively) while shoot bioaccumulation factor under ChS (ca. 280) indicates efficient Cd accumulation. High content of Cd in the trichomes from the AS treatment may be an anatomical adaptation mechanism. ChS evoked an increase in root biomass (hormesis), while the impact on shoot biomass was not significant in any treatment. The amounts of ascorbic acid and sum of phytochelatins were higher in the shoots but organic (malic and citric) acids dominated in the roots of plants from the ChS treatment. Chlorogenic acid, but not ursolic and oleanolic acids, was elevated by ChS. These data indicate that both chelation and enhancement of antioxidative power contribute to protection of plants exposed to long-term (chronic) Cd presence with subsequent hormetic effect.

Metabolic Changes Induced by Silver Ions in Carlina acaulis.

Silver is one of the most toxic heavy metals for plants, inducing various toxic symptoms and metabolic changes. Here, the impact of Ag(I) on Carlina acaulis physiology and selected metabolites was studied using two Ag concentrations (1 or 10 µM) after 14 days of exposure. The higher concentration of Ag(I) evoked reduction of growth, while 1 µM Ag had a growth-promoting effect on root biomass. The translocation factor (<0.04) showed that Ag was mainly retained in the roots. The 1 µM Ag concentration increased the level of low-molecular-weight organic acids (LMWOAs), while 10 µM Ag depleted these compounds in the roots. The increased concentration of Ag(I) elevated the accumulation of phytochelatins (PCs) in the roots and reduced glutathione (GSH) in the shoots (but not in the roots). At 1 µM, Ag(I) elevated the level of phenolic and triterpene acids, while the 10 µM Ag treatment increased the carlina oxide content in the roots. The obtained results indicate an alteration of metabolic pathways of C. acaulis to cope with different levels of Ag(I) stress. Our data imply that the intracellular binding of Ag(I) and nonenzymatic antioxidants contribute to the protection against low concentrations of Ag ions.

Micronutrient Status and Selected Physiological Parameters of Roots in Nickel-Exposed Sinapis alba L. Affected by Different Sulphur Levels.

An efficient method of improving the micronutrient status of Ni-treated white mustard (Sinapis alba L.) using intensive S-SO4 nutrition was developed. Twelve variants of Hoagland's nutrient solution differing in the concentration of S-SO4 (standard: 2 mM S, and elevated level: 6 or 9 mM S) and Ni (0, 0.0004, 0.04, or 0.08 mM Ni) were tested. The beneficial effect of intensive S nutrition on Ni-stressed plants was manifested by a significant rise in the content of Fe, Mn, and Zn, especially in the shoots. An increase was also found in the shoot B, Cu, and Mo content, whilst there were no changes in their root concentrations. Simultaneously, the shoot Cl concentrations dropped. The elevated level of S in the nutrient solution in general enhanced the translocation of Fe, Cu, Mo, and B in Ni-exposed plants. The beneficial effect of intensive S nutrition on the growth and micronutrient balance of Ni-exposed plants can be at least partially related to the positive changes in root surface properties, especially in cation exchange capacity (CEC). Meanwhile both reduced glutathione (GSH) and phytochelatins (PCs) probably do not significantly contribute to Ni resistance of white mustard under intensive S nutrition.

Sulfur nutrition level modifies the growth, micronutrient status, and cadmium distribution in cadmium-exposed spring wheat.

The effect of S nutrition level (standard-2 and intensive-6 or 9 mmol S L-1) on the growth, micronutrient status, and Cd concentration of Cd-exposed (0, 0.0002, 0.02, and 0.04 mmol Cd L-1) Triticum aestivum L. 'Zebra' was examined. The hypothesis that Cd-induced micronutrient imbalance in this species is alleviated by enhanced S-sulfate (S-SO4) nutrition was tested. The intensive S nutrition, especially the dose of 6 mmol L-1, to some extent alleviated Cd-induced stress by improving the adverse changes in micronutrient status and increase of the biomass. The root and shoot Fe, Cu, Mn, and Zn concentrations of Cd-exposed wheat rose at 6 and remained unaltered at 9 mmol S L-1. Particularly noteworthy is the substantial increase of Fe bioconcentration found in Cd-stressed plants at 6 mmol S L-1. The root Cu concentration increased at 6 and decreased at 9 mmol S L-1, but did not change in shoots. Simultaneously, both the high S levels elevated the shoot Cl concentration but had no effect on the root Cl concentration. There were no substantial changes in the Mo concentration. The intensive S nutrition of the Cd-treated wheat did not affect the translocation factor (TF) of Fe and B. In turn, root-to-shoot translocation of Mo and Zn was enhanced at 6 and remained unchanged at 9 mmol S L-1. The changes in TF of Cl, Cu, and Mn varied greatly, depending on the S and Cd concentrations. Intensive S nutrition of Cd-stressed wheat, as a rule, dropped the root and increased the shoot Cd concentration as well as reduced Cd bioconcentration/bioaccumulation factor enhancing root-to-shoot Cd translocation.

Silicon-induced antioxidant defense and methylglyoxal detoxification works coordinately in alleviating nickel toxicity in Oryza sativa L.

Nickel (Ni), an essential nutrient of plant but very toxic to plant at supra-optimal concentration that causes inhibition of seed germination emergence and growth of plants as a consequence of physiological disorders. Hence, the present study investigates the possible mechanisms of Ni tolerance in rice seedlings by exogenous application of silicon (Si). Thirteen-day-old hydroponically grown rice (Oryza sativa L. cv. BRRI dhan54) were treated with Ni (NiSO4.7H2O, 0.25 and 0.5 mM) sole or in combination with 0.50 mM Na2SiO3 for a period of 3 days to investigate the effect of Si supply for revoking the Ni stress. Nickel toxicity gave rise to reactive oxygen species (ROS) and cytotoxic methylglyoxal (MG), accordingly, initiated oxidative stress in rice leaves, and accelerated peroxidation of lipids and consequent damage to membranes. Reduced growth, biomass accumulation, chlorophyll (chl) content, and water balance under Ni-stress were also found. However, free proline (Pro) content increased in Ni-exposed plants. In contrast, the Ni-stressed seedlings fed with supplemental Si reclaimed the seedlings from chlorosis, water retrenchment, growth inhibition, and oxidative stress. Silicon up-regulated most of the antioxidant defense components as well as glyoxalase systems, which helped to improve ROS scavenging and MG detoxification. Hence, these results suggest that the exogenous Si application can improve rice seedlings' tolerance to Ni-toxicity.

Allantoin attenuates cadmium-induced toxicity in cucumber plants.

Concentration-dependent responses of cucumber plants to cadmium (Cd, 5-15 µM) and/or allantoin (Alla, 10-1000 µM) have been investigated to detect a possible protective role of Alla under Cd excess. After 14 days of exposure, Alla often considerably reversed Cd-induced inhibition of growth and reduction of the content of photosynthetic pigments. Higher Alla doses depleted the Cd amount in shoots, which could be related to citric acid (increase in the shoots but depletion in the roots in Cd+Alla treatments) rather than to phytochelatins (Alla had a negative impact on the phytochelatin accumulation). An increase in the Alla concentration suppressed Cd-induced spatial H2O2 appearance, which does not seem to be related to antioxidative enzymes (low impact of Alla on catalase, ascorbate peroxidase, and guaiacol peroxidase). On the contrary, shoot glutathione and mainly ascorbic acid accumulation strongly increased in Cd+Alla treatments, indicating their prominent role in Alla-induced amelioration of Cd-stimulated oxidative stress and growth retardation. Similarly, phenolic metabolites (total soluble phenols and flavonols) were slightly influenced by Alla and their antioxidative action was not expected. We conclude that Alla-mediated attenuation of Cd-induced toxicity relies on enhanced accumulation of glutathione and ascorbate in the shoot tissue mainly, rather than on elevated antioxidative enzyme activities.

Selenium biofortification enhances the growth and alters the physiological response of lamb's lettuce grown under high temperature stress.

We examined the possibility to enhance the growth and the physiological tolerance of lamb's lettuce (Valerianella locusta L.) grown under heat stress (HS) by biofortification with selenium (Se). The plants were grown at optimal (22/19 °C; day/night) or high (35/22 °C; day/night) temperature and Se was applied via foliar or soil treatment. The HS reduced plant biomass and photosynthetic pigment concentration and impaired some parameters of chlorophyll a fluorescence. The lamb's lettuce grown under HS accumulated large amounts of H2O2 in the leaves, especially in younger ones. The Se fertilization (both foliar and soil) at HS was beneficial to plant growth, whilst the concentration of photosynthetic pigments and the analysed parameters of chlorophyll a fluorescence were unaffected by the Se supply. The application of Se enhanced the thermo-tolerance of plants through cooperative action of antioxidant enzymes, such as guaiacol peroxidase (GPOX; EC 1.11.1.7) and catalase (CAT; EC 1.11.1.6), and reduced glutathione (GSH) among low-molecular-weight non-enzymatic antioxidants, in removal of excess of H2O2. Although under HS the content of different phenolic compounds in the leaves was higher than under normal temperature (NT), the application of Se did not affect their concentration at stress conditions. On the other hand, at NT the Se-biofortified plants accumulated significantly more phenolic compounds with health-promoting properties than Se-untreated plants. Therefore, biofortification of lamb's lettuce with Se can be beneficial in terms of plants yield and their nutritional value under both NT and HS.

Interaction Between Cadmium Stress and Sulphur Nutrition Level on Macronutrient Status of Sinapis alba L.

This study evaluated the possibility of improving the macronutrient status of Cd-stressed white mustard 'Rota' using intensive S nutrition. Three S-SO4 (2, 6, 9 mM S) and four CdCl2 doses (0, 0.0002, 0.02, 0.04 mM Cd) in the Hoagland's nutrient solution were conducted for 14 days. High S supply (6 or 9 mM) appears, to some extent, to affect positively the macronutrient status of Cd-stressed mustard. It increased roots and shoots contents of K and S, without significant changes in P content. Simultaneously, Mg content in shoots and roots remained stable, but Mg bioaccumulation was elevated. Shoot Ca content at the lowest and medium Cd dose decreased, whilst was unaffected at the highest Cd treatment. Intensive S nutrition of Cd-stressed mustard increased root N content and accumulation at the highest Cd concentration, but the N content dropped in above-ground parts. The bioaccumulation of remained macronutrients in general was substantially elevated together with enhanced Cd accumulation. Thus, the intensive S nutrition can enhance mustard tolerance to Cd stress by improvement macronutrients relations in plants, and S supplementation may be recommended for mustard cultivation on the Cd-contaminated areas.

Macroelemental composition of cadmium stressed lettuce plants grown under conditions of intensive sulphur nutrition.

Lettuce (Lactuca sativa L.) is moderately sensitive to cadmium (Cd) and shows high accumulation of this metal. Thus, this species is considered to be a good model for both identifying determinants controlling Cd accumulation in plant tissues and for developing breeding strategies aimed at limiting the accumulation of this metal in edible tissues. Simultaneously, lettuce is characterised by medium requirements for sulphur (S) - a macronutrient whose role is associated not only with proper growth and development, but also with stress tolerance. The common use of NPK fertilizers without sulphates (S-SO4) together with the progressive process of reducing emissions of S compounds to the natural environment may lead to deficiency of this element in plants. The present study evaluated the changes in macronutrient content and accumulation in Cd-stressed lettuce 'Justyna' supplied with different S doses. Four concentrations of Cd (0, 0.0002, 0.02 or 0.04 mM) and three levels of S applied in the form of S-SO4 (2, 6 or 9 mM S) were used. Cd exposure impaired the macronutrient balance and accumulation in lettuce. Intensive S nutrition to some extent alleviated Cd-induced toxicity. High S doses, especially 6 mM S, partially improved macronutrient status and restored the macronutrient balance. In Cd-stressed plants supplemented with additional S, an increase in root and shoot biomass and in the content of N, K and Mg was found, without significant changes in the Ca content. Simultaneously, the P and S contents in the biomass of both above- and underground organs remained unchanged. In the leaves, as opposite to the roots, intensive S nutrition reduced the accumulation of Cd. However, the foliar Cd concentration still exceeded the acceptable limits established for consumption. All the obtained results concerning the content of macronutrients and their ratios were referred, inter alia, to the standards i.e. the Diagnosis and Recommendation Integrated System (DRIS) norms.