A multivariate analysis of health risk assessment,phytoremediation potential,and biochemical attributes of Spinacia oleracea exposed to cadmium in the presence of organic amendments under hydroponic conditions

Abstract

Cadmium (Cd) phytoremediation potential and its accumulation in edible and nonedible plant tissues is the function of various biochemical processes taking place inside plants. This study assessed the impact of organic ligands on Cd phyto uptake and different biophysiochemical processes of Spinacia oleracea L., and associated health hazards. Plants were exposed to Cd alone and chelated with citric acid (CA) and ethylenediaminetetraacetic acid (EDTA). Results revealed that the effect of Cd on lipid peroxidation, H₂O₂ production and pigment contents varied greatly with its applied level and the type of organic ligand. Moreover, the effect was more prominent in root tissues than leaf tissues and for high concentrations of Cd and organic ligands. Cadmium accumulation increased by 90 and 74% in roots and leaves, respectively, with increasing Cd levels (25–100?µM). Cadmium exposure at high levels caused lipid peroxidation in roots only. Application of both CA and EDTA slightly diminished Cd toxicity with respect to pigment contents, lipid peroxidation and hydrogen peroxide (H₂O₂) contents. Hazard quotient (HQ) of Cd was <1.00 for all the treatments. Under nonlinear effect of treatments, multivariate analysis can be an effective tool to trace overall effects/trends.     

Morpho-physiological and antioxidant response to NaCl-induced stress in in vitro shoots of pomegranate (<Emphasis Type="Italic">Punica granatum</Emphasis> L.)

The physiological and antioxidant response to salinity was studied in pomegranate (Punica granatum L.) by exposing in vitro growing shoots of the Italian variety Profeta Partanna to 125 or 250 mM NaCl for 10 and 20 days. 250 mM NaCl significantly reduced shoot length, leaf area and water content of the shoots, regardless the length of the salt treatment,with respect to the control and to the 125 mM NaCl treatment. After 20 days the shoots treated with 250 mM NaCl also showed a significant reduction in relative growth rate (RGR) together with marked necroses and abscission of the oldest leaves. Salt treatments significantly decreased the contents of chlorophylls and carotenoids in both exposure times, depending on NaCl concentration. Proline, total phenolic compounds and ellagic acid did not increase or even decrease with the salt treatments. The levels of lipid peroxidation decreased, ascorbate peroxidase (APX) activity significantly increased in both treatment times and concentrations, while guaiacol peroxidase (G-POD) activity significantly increased in shoots treated with 250 mM NaCl for 20 days suggesting the rapid involvement of APX in controlling the oxidative stress in this species, even at low salt concentrations, and a delayed complementary role of G-POD.     

Glutathione and citric acid modulates lead- and arsenic-induced phytotoxicity and genotoxicity responses in two cultivars of <Emphasis Type="Italic">Solanum lycopersicum</Emphasis> L.

This study was conducted through the pot experiments to understand the mechanism of lead (Pb) and arsenic (As)-induced phytotoxicity and their possible alleviation by glutathione (GSH) and citric acid (CA) in two cultivars of Solanum lycopersicum L., i.e., Pusa ruby (PR) and Arka vikas (S22). Therefore, tomato seedlings were germinated in soil-rite supplemented with seven treatments, i.e., control, 10 µM Pb, 10 µM As, 10 µM Pb + 250 µM GSH, 10 µM As + 250 µM GSH, 10 µM Pb + 250 µM CA and 10 µM As + 250 µM CA for 7 days and examined for growth parameters, lipid peroxidation, photosynthetic pigments and antioxidative mechanism. Results of our study showed that Pb and As alone decrease seed germination, growth parameter, chlorophylls and increase anthocyanins and lipid peroxidation in both the cultivars. Pb- and As-induced oxidative stress resulted into significant changes in the plant responses that attributed by increased activity of antioxidative enzymes and non-enzymatic antioxidants. GSH and CA showed potential to alleviate Pb- or As-induced phytotoxicity and strengthen the plant antioxidative machinery and structural integrity. Cultivar PR showed better response than cv. S22. Pb and As treatment caused significant damages to the DNA molecules and structural integrity of the cv. PR roots. These findings can be useful for understanding the Pb- and As-induced phytotoxic biomarkers along with GSH- and CA-mediated alleviation mechanisms, which will provide new insight in developing better system for phytoremediation technology.     

Effect of sodium nitroprusside on responses of <Emphasis Type="Italic">Melissa officinalis</Emphasis> to bicarbonate exposure and direct Fe deficiency stress

In our study, one-month-old Melissa officinalis plants were subjected to Fe-deficiency treatments, such as 10 µM Fe (as direct iron deficiency, DD), and 30 µM Fe + 10 mM NaHCO₃ + 0.5 g l^?1 CaCO₃ (as indirect iron deficiency, ID), and 30 µM Fe (as control) for 14 d. Both Fe-deficiency types reduced plant growth, photosynthetic pigment contents, an active Fe content in roots and leaves, root Fe(III)-reducing capacity, Fe-use efficiency, maximal quantum yield of PSII photochemistry, a ratio of variable to basic fluorescence, and activities of antioxidant enzymes, while they increased lipid peroxidation and a H₂O₂ content in leaves. These effects were more pronounced in plants exposed to ID with bicarbonate than those of DD plants. We showed that sodium nitroprusside (SNP), as NO donor, could ameliorate the adverse effects of bicarbonate on above traits. The methylene blue, as NO blocker, reversed the protective effects conferred by SNP in the ID-treated plants as well as DD plants. These findings suggests that NO protects photosynthesis and growth of IDtreated plants as well as DD plants by contribution in availability and/or delivery of metabolically active iron or by changing activities of reactive oxygen species-scavenging enzymes.     

Concentration Levels of Essential and Non-essential Metals in Ethiopian Khat (Catha edulis Forsk)

The levels of essential (Ca, Mg, Mn, Fe, Zn, Cr, Cu, and Co) and non-essential (Cd and Pb) metal in six different varieties of Ethiopian khat (Catha edulis Forsk, an evergreen stimulant plant) commonly consumed in the country and exported to the neighboring countries were determined by flame atomic absorption spectrometry. Known weight of oven-dried khat samples were wet-digested using 2 mL of (69–72%) HNO₃ and 2 mL of (70%) HClO₄ for 2 h and 30 min at variable temperature (120–270°C). The mineral contents in the digests were analyzed using flame atomic absorption spectrometer. The following concentrations ranges in fresh-weight basis were recorded in decreasing order: Ca (1,038–2,173 µg/g)?>?Mg (478.2–812.3 µg/g)?>?Fe (53.95–82.83 µg/g)?>?Zn (5.18–9.40 µg/g)?>?Mn (6.98–8.66 µg/g)?>?Cu (1.85–5.53 µg/g)?>?Cr (0.66–3.47 µg/g)?>?Co (0.41–0.80 µg/g). A wide variation in the mineral contents of khat from different region of Ethiopia was noticed. The toxic metals (Pb and Cd) were not detected in all the samples analyzed.     

Effects of exogenous nitric oxide on photosynthesis,antioxidative ability,and mineral element contents of perennial ryegrass under copper stress

A hydroponics experiment was conducted to test the effects of sodium nitroprusside (SNP, a donor of NO) supplied with different concentrations on copper (Cu) toxicity in ryegrass seedlings (Lolium perenne L.). Excess Cu (200 µM) reduced chlorophyll content, resulting a decrease in photosynthesis. Cu stress induced the production of hydrogen peroxide (H₂O₂) and superoxide anion (O₂^{? ?}), leading to malondialdehyde (MDA) accumulation. Furthermore, activities of antioxidant enzymes in Cu-treated seedlings such as superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT) were decreased. In addition, Cu stress inhibited the uptake of K, Mg, Fe, and Zn and increased Ca content in roots. Moreover, in leaves of Cu-stressed seedlings, K, Fe, and Zn contents were decreased and the contents of Ca and Mg were not affected significantly. In Cu-treated seedlings, Cu concentration in roots was higher than in leaves. Addition of 50, 100, 200 µM SNP in Cu-mediated solutions increased chlorophyll content and photosynthesis, improved antioxidant enzyme activities, reduced Cu-induced oxidative damages, kept intracellular ion equilibrium under Cu stress, increased Cu concentration in roots and inhibited Cu accumulation in leaves. In particular, addition of 100 µM SNP had the best effect on promoting growth of ryegrass seedlings under Cu stress. However, the application of 400 µM SNP had no obvious alleviating effect on Cu toxicity in ryegrass seedlings.     

Physiological responses of peanut seedlings to exposure to low or high cadmium concentration and the alleviating effect of exogenous nitric oxide to high cadmium concentration stress

Abstract

The physiological responses of peanut seedlings exposed to low (5 µM) or high (200 µM) cadmium (Cd) concentration and the ability of sodium nitroprusside (SNP, a donor of NO) to reverse the harmful effects of Cd on peanut (Arachis hypogaea L.) were studied. Changes in plant growth parameters, chlorophyll content, antioxidant system, nutrient contents and Cd accumulation were investigated. The results showed that SNP and 5 µM Cd improved plant growth and chlorophyll content. Furthermore, antioxidative system was up-regulated, and as a result, the production rate of superoxide radical (O₂^??) was reduced. Moreover, the absorption of nutrient elements was not impacted, and Cd toxicity was not observed. However, 200 µM Cd had negative effects on the above measured parameters and dramatically increased the accumulation of Cd in all the plant organs. In the 200 µM Cd treatment, addition of 250 µM SNP stimulated plant growth and increased chlorophyll content. It also enhanced the regulation of antioxidative system and reduced the production rate of O₂^?? and malondialdehyde (MDA) content. Besides, SNP supply enhanced the absorption of nutrient elements and restrained the absorption and transport of Cd.     

Epibrassinolide Application Regulates Some Key Physio-biochemical Attributes As Well As Oxidative Defense System in Maize Plants Grown Under Saline Stress

It was aimed to investigate the ameliorative effect of exogenously applied 24-epibrassinolide (EBR) on some key growth parameters and mineral elements in two salt-stressed maize (PR 32T83 and PR 34N24) cultivars. A factorial experiment was designed with two electrical permeability (EC) levels (1.1 and 8.0 dS/m) and two levels (1.5 and 2.0 µM) of EBR supplied as a seed treatment, foliar spray, or both in combination. The foliar application of EBR was done once a week during the experiment. After 42 days of these treatments, the plants were harvested to assess growth, water relations, and oxidative and antioxidative systems. Salt stress markedly reduced plant fresh and dry weights, maximum fluorescence yield of PS-II, chlorophyll contents, leaf water potential, and leaf K and Ca, but it increased membrane permeability, the activities of superoxide dismutase (SOD; EC 1.15.1.1), peroxidase (POD; EC. 1.11.1.7), and catalase (CAT; EC. 1.11.1.6) enzymes, and the contents of proline and glycine betaine, leaf sap osmotic pressure, lipid peroxidation, hydrogen peroxide, and leaf Na and Cl. However, both seed treatment and foliar application of EBR to the maize plants exposed to saline conditions enhanced key growth attributes, water relations, and the activities of various antioxidant enzymes as well as the levels of proline, but they reduced electrolyte leakage, and H₂O₂ and MDA contents. Saline stress reduced leaf N, Ca²⁺, K⁺, and P contents as compared to those in the non-stressed plants. Both seed treatment and foliar application of EBR reduced Na⁺ and Cl^? concentrations, but increased those of N, Ca²⁺, K⁺, and P. Foliar application of EBR was more effective in increasing nutrient levels of plants grown at the high saline regime compared to the seed treatment of EBR. The study clearly indicates that both seed treatment and foliar application of EBR at the rate of 2.0 µM can overcome the detrimental effect of salinity stress on maize growth, which was found to be significantly linked to reduced concentrations of Na, Cl, MDA, and H₂O₂ as well as EL and increased activities of key antioxidant enzymes in the maize plants.     

Methyl jasmonate alleviates arsenic-induced oxidative damage and modulates the ascorbate–glutathione cycle in oilseed rape roots

Methyl jasmonate (MJ) is an important plant growth regulator, involves in various physiological processes of plants. In the present study, role of MJ in tolerance to oilseed rape (Brassica napus L.) roots under arsenic (As) stress was investigated. The treatments were comprised of three MJ doses (0, 0.1, and 1 µM) and two levels of As (0 and 200 µM). Arsenic stress resulted in oxidative damage as evidenced by decreased root growth and enhanced reactive oxygen species and lipid peroxidation. However, plants treated with MJ decreased the H₂O₂ and O₂ ^·? contents in roots and have higher antioxidant activities. Importantly, results showed that MJ enhanced the redox states of AsA and GSH, and the related enzymes involved in the AsA–GSH cycle. Moreover, MJ also induced the secondary metabolites related enzymes (PAL and PPO) activities, under As stress. PAL and PPO expression was further increased by MJ application in the roots of B. napus under As stress. MJ also reduced the total As content compared with As alone treated plants. These findings suggest the role of MJ in mitigation of the As-induced oxidative damage by regulating AsA and GSH redox states and by reducing As uptake in both cultivars.     

Photosynthetic capacity of the capsule wall and its contribution to carbon fixation and seed yield in castor (<Emphasis Type="Italic">Ricinus communis</Emphasis> L.)

Defoliation occurs in castor due to several reasons, but the crop has propensity to compensate for the seed yield. Photosynthetic efficiency in terms of functional (gas exchange and chlorophyll fluorescence) and structural characteristics (photosynthetic pigment profiles and anatomical properties) of castor capsule walls under light- and dark-adapted conditions was compared with that of leaves. Capsule wall showed high intrinsic efficiency of photosystem II (F _v/F _m, 0.82) which was comparable to leaves (F _v/F _m, 0.80). With increasing photon flux densities (PFD), actual quantum yields and photochemical quenching coefficients of the capsule walls were similar to that in leaves, while electron transport rates reached a maximum corresponding to about 118 % of the leaves. However, maximum net photosynthetic rate of the capsule walls (2.60 µmol CO₂ m^?2 s^?1) was less than one-fourth of the leaves (15.67 µmol CO₂ m^?2 s^?1) at the CO₂ concentration of 400 µmol mol^?1, and the difference was attributed to about 80 % lower stomatal density and the 75 % lower total chlorophyll content of capsule walls than the leaves. Furthermore, seed weight in dark-adapted capsules was 2.70–12.42 % less as compared to the capsules developed under light. The results indicate that castor capsule walls are photosynthetically active (about 15–30 % of the leaves) and contribute significantly to carbon fixation and seed yield accounting for 10 % photoassimilates towards seed weight.     

Calcium supplementation modulates arsenic-induced alterations and augments arsenic accumulation in callus cultures of Indian mustard (Brassica juncea (L.) Czern.)

In the present study, the effect of arsenate (AsV) exposure either alone or in combination with calcium (Ca) was investigated in callus cultures of Brassica juncea (L.) Czern. cv. Pusa Bold grown for a period up to 24 h. The AsV?(250 μM) + Ca (10 mM) treatment resulted in a significantly higher level of As (464 μg g^?1 dry weight (DW)) than AsV without Ca (167 μg g^?1 DW) treatment at 24 h. Furthermore, AsV + Ca-treated calli had a higher percent of AsIII (24–47%) than calli subjected to AsV treatment (12–14%). Despite this, AsV + Ca-treated calli did not show any signs of hydrogen peroxide (H₂O₂) accumulation or cell death upon in vivo staining, while AsV-exposed calli had increased H₂O₂, shrinkage of cytoplasmic contents, and cell death. Thus, AsV treatment induced oxidative stress, which in turn elicited a response of antioxidant enzymes and metabolites as compared with control and AsV + Ca treatment. The positive effects of Ca supplementation were also correlated to an increase in thiolic constituents', viz., cysteine, reduced glutathione, and glutathione reductase in AsV + Ca than in AsV treatment. An analysis of selected signaling related genes, e.g., mitogen-activated protein kinases (MAPK3 and MAPK6) and jasmonate ZIM-domain (JAZ3) suggested that AsV and AsV + Ca followed variable pathways to sense and signal the As stress. In AsV-alone treatment, jasmonate signaling was seemingly activated, while MAPK3 was not involved. In contrast, AsV + Ca treatment appeared to specifically inhibit jasmonate signaling and activate MAPK3. In conclusion, Ca supplementation may hold promise for achieving increased As accumulation in plants without compromising their tolerance.     

Root morphology, root-hair development and rhizosheath formation on perennial grass seedlings is influenced by soil acidity

Cadmium (Cd) exerts a detrimental effect on the metabolism of plants, whereas selenium (Se) may protect them against various stressors through its antioxidative activity. In this in vitro study we investigated the impact of Se (2 µM Na₂SeO₄) on the growth, nutrient (P, S, K, Ca, Mg, B, Mn, Fe and Zn) concentrations and cell integrity of rape (Brassica napus oleifera) and two wheat (Triticum aestivum) genotypes subjected to Cd stress (600 µM CdCl₂). Rape accumulated both Cd and Se more than did wheat. In all plants, Cd markedly reduced the biomass, enhanced lipid peroxidation and diminished plasmalemma fluidity. A drop in the K uptake and the reduced plasmalemma permeability diminished the K efflux from the leaf cells. In contrast, Cd elevated S concomitantly with Zn, indicating an activity of detoxifying SH groups and SOD isoenzymes. When added alone, Se promoted the growth of all plants, it enhanced the accumulation of S, but the impact on other nutrients remained minor. In Cd-stressed plants, Se tended to counterbalance the Cd-induced changes in nutrients, it also reduced the lipid peroxidation and exerted positive effects on the cell membrane stability. The Cd stress and the protective role of Se were most evident in rape. The Finnish wheat genotype was less tolerant to Cd than the Polish one.     

Effect of heavy metal pollution on mineral absorption in sunflower (Helianthus annuus L.) hybrids

The present study was conducted in a potted experiment to examine the effects of chromium pollution on absorption of mineral nutrients and some morpho-physiological attributes of two sunflower (Helianthus annuus L.) hybrids (FH-331 and FH-259) in the presence and absence of ethylene diamine tetra acetic acid (EDTA) used as a chelating agent. Four concentrations of chromium (Cr³⁺) i.e., 0, 20, 30 and 40 mg kg^?1 with and without 0.3 g kg^?1, EDTA as chelating agent were applied to 25-day-old sunflower plants. A gradually decreasing trend in absorption of all minerals and other parameters studied were observed. Different treatments of Cr³⁺ as well as Cr³⁺ and EDTA significantly reduced root and shoot fresh weight; however, root, shoot and achene Cr³⁺ contents of two sunflowers hybrids under higher chromium and EDTA stress varied significantly whereas movement of Cr³⁺ contents to leaves was non-significant. Absorption of Na⁺, K⁺, N₂ and P through roots and shoots significantly reduced with increasing concentration of Cr³⁺ treatments. In fact addition of EDTA to the medium further enhanced the toxicity of chromium.     

Effects of Adding Nitroprusside on Arsenic Stressed Response of Pistia stratiotes L. Under Hydroponic Conditions

Effect of nitric oxide (NO) in mitigating stress induced by arsenic (As) was assessed in Pistia stratiotes, with NO supplied as sodium nitroprusside (SNP). Plants were exposed to four treatments: control, SNP (0.1 mg L^?1), As (1.5 mg L^?1), As + SNP (1.5 and 0.1 mg L^?1), for seven days (analyses of growth, absorption of As and mineral nutrients) and for 24 h (analyses of concentration of reactive oxygen intermediates (ROIs), antioxidant capacity and photosynthesis). P. stratiotes accumulated high concentrations of As and this accumulation wasn't affected by the addition of SNP, but the tolerance index of the plant to As increased. SNP attenuated effects of As on the absorption of mineral nutrients (Ca, Fe, Mn, and Mg), but not for phosphorus, and maintained concentrations of ROIs to normal levels, probably due to the increase in antioxidant capacity. The As damaged the photosynthesis by the decrease in pigment contents and by disturbance the photochemical (loss of PSII efficiency and increases in non-photochemical quenching coefficient) and biochemical (reductions in carbon assimilation, increase in the C_i/C_a and Φ_PSII/Φ_CO2 ratios) steps. The addition of SNP restored these parameters to normal levels. Thus, NO was able to increasing the resistance of P. stratiotes to As.

Supplemental materials are available for this article. Go to the publisher's online edition of International Journal of Phytoremediation to view the supplemental file.     

Responses of in vitro-cultured <Emphasis Type="Italic">Allium hirtifolium</Emphasis> to exogenous sodium nitroprusside under PEG-imposed drought stress

Drought stress is a major threat to plant production in semi-arid and arid areas of the world. This research was laid out to asses the effects of sodium nitroprusside (SNP) as a nitric oxide donor on growth, physiological and biochemical changes of in vitro-cultured Allium hirtifolium under polyethylene glycol (PEG) induced drought stress. Basal plate explants of A. hirtifolium were cultured on MS medium containing different levels of PEG (0, 2, 4, 8 and 16 mM) and SNP (0, 10, 40 and 70 µM). After prolonged drought, growth responses, oxidative stress indicators, and phytochemical variations of regenerated plantlets with or without PEG and/or SNP treatments were recorded. Water limitation reduced regeneration potential of explants and consequently number of shoots per explant. Relative water content, total chlorophyll and carotenoid contents of regenerated A. hirtifolium plantlets decreased, but accumulation of malondialdehyde, H₂O₂ and proline and the activities of superoxide dismutase, ascorbate peroxidase, catalase and peroxidase enzymes increased with decreasing water availability. Total phenol and allicin contents were also increased in response to drought stress. Exogenous SNP in 10 and particularly in 40 µM was effective in enhancing regeneration rate and relative water content as well as protecting photosynthetic pigments under different levels of water availability. SNP also inhibited the hydrogen peroxide (H₂O₂) accumulation and lipid peroxidation in cell membranes via increasing the activities of superoxide dismutase and ascorbate peroxidase enzymes and accumulating proline and allicin. In general, these results suggest that exogenous SNP at 40 µM not only could somewhat protect A. hirtifolium from drought stress, but also can help to improve the propagation and allicin production of that plant under in vitro condition.     

Enhanced Phytoremediation of Cadmium-Contaminated Soil by Parthenium hysterophorus Plant: Effect of Gibberellic Acid (GA3) and Synthetic Chelator,Alone and in Combinations

The roles of gibberellic acid (GA₃) and ethylenediaminetetraacetic acid (EDTA) in phytoremediation of cadmium (Cd)-contaminated soil by Parthenium hysterophorus plant was investigated. GA₃ (10^?9, 10^?7, and 10^?5M) was applied as a foliar spray. EDTA was added to soil in a single dose (160 mg/kg soil) and split doses (40 mg/kg soil, four split doses). GA₃ and EDTA were used separately and in various combinations. P. hysterophorus was selected due to its fast growth and unpalatable nature to herbivores to reduce the entrance of metal into the food chain. The Cd phytoextraction potential of the P. hysterophorus plant was evaluated for the first time. Cd significantly reduced plant growth and dry biomass (DBM). GA₃ alone increased the plant growth and biomass in Cd-contaminated soil, whereas EDTA reduced it. GA₃ in combination with EDTA significantly increased the growth and biomass. The highest significant DBM was found in treatment T3 (10^?5M GA₃). All treatments of GA₃ or EDTA significantly enhanced the plant Cd uptake and accumulation compared with control (C1). The highest significant root and stem Cd concentrations were found in the combination treatment T11 (GA₃ 10^?5M + EDTA split doses), whereas in leaves it was found in the EDTA treatments. Cd concentration in plant parts increased in the order of stem < leaves < roots. The combination treatment T9 (GA₃ 10^?7M + EDTA split doses) showed the significantly highest total Cd accumulation (8 times greater than control C1, i.e., only Cd used). The GA₃ treatments accumulated more than 50% of the total Cd in the roots, whereas the EDTA treatments showed more than 50% in the leaves. Root dry biomass showed a positive and significant correlation with Cd accumulation. GA₃ is environment friendly as compared with EDTA. Therefore, further investigation of GA₃ is recommended for phytoremediation research for the remediation of metal-contaminated soil.     

Mechanical properties of Callitriche cophocarpa leaves under Cr(VI)/Cr(III) influence

Submersed Callitriche cophocarpa is an outstanding Cr phytoremediator in water systems. The mineral elements in waters can penetrate the submersed plant surface. This has led us to the hypothesis that the absorbed Cr can alter the mechanical properties of leaves. These properties were measured by applying atomic force microscopy. C. cophocarpa shoots were immersed in 100 µM (5.2 mg/l) Cr solution for 7 days. Cr was applied independently at two distinct oxidation states as Cr(VI) and Cr(III), known from different physicochemical properties and toxic effects. The contents of elements which were proportional to the fluorescence signal in individual leaves were evaluated using micro-X-ray fluorescence spectroscopy. The results obtained showed that the leaf epidermis significantly changes its elastic properties upon incubation with Cr-supplemented solution. When compared to the control, a drop in the leaf’s stiffness observed for Cr(III) was ca. 42 %. In the case of Cr(VI)-treated leaves, the stiffness raised to ca. 17 %. The changes in elasticity were significantly correlated with the contents of Ca (Pearson’s coefficient r = 0.87, p < 0.017). The results led us to ascertain that it is Cr(III) but not Cr(VI) that significantly influences Ca removal from leaves thus decreasing the stiffness of the leaf’s epidermis.     

Cobalt stress affects nitrogen metabolism,photosynthesis and antioxidant system in chickpea (Cicer arietinum L.)

Abstract

Plants of chickpea were exposed to varied levels of cobalt (Co) and sampled at the 60-day stage. Cobalt at concentration <100 µM significantly increased the number of nodules, their dry mass, leghemoglobin concentration and the activity of nitrogenase. Similarly, the activities of glutamate dehydrogenase, glutamine synthetase and glutamate synthase also exhibited an increase in the presence of Co <100 µM, in nodules and leaves, respectively. The various photosynthetic attributes in leaves and the activity of antioxidative enzymes both in nodules and leaves were inhibited by Co in a concentration-dependent manner. However, the lipid peroxidation and the content of proline exhibited a significant increase in response to Co and were at a maximum in the plants exposed to 250 µM concentration of cobalt. Since most of the parameters showed a significant increase in response to 50 µM cobalt, this concentration may be regarded as a threshold concentration.     

Stimulatory role of smoke–water and karrikinolide on the photosynthetic pigment and phenolic contents of micropropagated ‘Williams’ bananas

At low concentrations, smoke–water (SW) and smoke-derived karrikinolide (KAR₁) are compounds with potential cytokinin and auxin-like activity. Their roles on the growth, photosynthetic pigment and phenolic contents of micropropagated ‘Williams’ bananas were investigated in comparison with meta-topolin (mT). Explants were cultured on modified Murashige and Skoog basal media supplemented with either SW (1:125; 1:250; 1:500; 1:1,000; 1:2,000 dilutions) or KAR₁ at four concentrations ranging from 4.8?×?10^?22 to 3.3?×?10^?12?M. After 42?days, growth parameters were measured while the photosynthetic pigments and phenolic contents were quantified using spectrophotometric methods. Chlorophyll a, b and total carotenoid contents were significantly enhanced by KAR₁ (4.8?×?10^?22?M) and SW (1:125 and 1:1,000 dilutions). The pigments in KAR₁-treated plantlets were approximately two-fold to three-fold higher than those in the control and mT-treated plants, respectively. Total phenolic content was highest with KAR₁ at 1.0?×?10^?19?M in the leaves and 7.8?×?10^?17?M in the roots. Furthermore, KAR₁-treated plants at 1.0?×?10^?19?M yielded the highest level of total phenolics (leaves) and proanthocyanidins (roots). At 1:500 dilutions, SW stimulated the highest total flavonoid content in the leaves across all the treatments. Combining mT with either SW (1:500) or KAR₁ (4.8?×?10^?22?M) significantly increased the quantity of secondary metabolites. However, the growth parameters and pigment contents were not improved. Based on the significant role of photosynthetic pigments and phenolic compounds on the defense and survival strategies of plants, current findings will have practical significance for important processes such as acclimatization and survival of micropropagated plants. These results are also demonstrating the potential of SW and KAR₁ as an eliciting agent for secondary metabolite production.     

Effect of NaCl stress on rice physiological properties

Salinity is a major yield-reducing factor in coastal and arid irrigated rice production systems. Rice seedlings (Oryza sativa cv. Tarom Atri) were exposed to different NaCl concentrations for 8 days after germination. Plants height, fresh and dry weight, relative water content, pigment and carbohydrate content, photosynthetic efficiency and lipid peroxidase and antioxidant enzyme activity of rice seedlings grown under salt stress were investigated. Seedling grown under 25and 50 mM salt were shorter than the control. They could, however, develop their secondary leaves. Seedlings grown in the nutrient solution supplied with 100 and 200 mM extra salt could not develop their secondary leaves. Fresh weight ofseedlings grown under salt stress reduced up to 42.2% of the non-treated seedlings. Chlorophylls and carotenoids contents decreased significantly in the salt-treated seedlings. Carotenoid contents in NaCl-treated seedlings were decreased to 39.3%. No significant changes occurred in the photochemical efficiency of control and stressed plants. Increasing concentrations of NaCl resulted in increase and decrease of Na⁺ and K⁺ ions, respectively. NaCl salinity caused an increase in both peroxide content and lipid peroxidation. Seedlings which recovered for 24 h showed lower peroxide and malondialdehyde content.