Reactive Oxygen Species Formation and Cell Death in Catalase-Deficient Tobacco Leaf Discs Exposed to Paraquat

In the present work, the response of tobacco (Nicotiana tabaccum L.) wild-type SR1 and transgenic CAT1AS plants (with a basal reduced CAT activity) was evaluated after exposure to the herbicide paraquat (PQ). Superoxide anion (O₂^.−) formation was inhibited at 3 or 21 h of exposure, but H₂O₂ production and ion leakage increased significantly, both in SR1 or CAT1AS leaf discs. NADPH oxidase activity was constitutively 57% lower in non-treated transgenic leaves than in SR1 leaves and was greatly reduced both at 3 or 21 h of PQ treatment. Superoxide dismutase (SOD) activity was significantly reduced by PQ after 21 h, showing a decrease from 70% to 55%, whereas catalase (CAT) activity decreased an average of 50% after 3 h of treatment, and of 90% after 21 h, in SR1 and CAT1AS, respectively. Concomitantly, total CAT protein content was shown to be reduced in non-treated CAT1AS plants compared to control SR1 leaf discs at both exposure times. PQ decreased CAT expression in SR1 or CAT1AS plants at 3 and 21 h of treatment. The mechanisms underlying PQ-induced cell death were possibly not related exclusively to ROS formation and oxidative stress in tobacco wild-type or transgenic plants.     

Physiological responses and antioxidant enzyme changes in <Emphasis Type="Italic">Sulla coronaria</Emphasis> inoculated by cadmium resistant bacteria

Plant growth promoting bacteria (PGPB) may help to reduce the toxicity of heavy metals on plants growing in polluted soils. In this work, Sulla coronaria inoculated with four Cd resistant bacteria (two Pseudomonas spp. and two Rhizobium sullae) were cultivated in hydroponic conditions treated by Cd; long time treatment 50 µM CdCl₂ for 30 days and short time treatment; 100 µM CdCl₂ for 7 days. Results showed that inoculation with Cd resistant PGPB enhanced plant biomass, thus shoot and root dry weights of control plants were enhanced by 148 and 35% respectively after 7 days. Co-inoculation of plants treated with 50 and 100 µM Cd increased plant biomasses as compared to Cd-treated and uninoculated plants. Cadmium treatment induced lipid peroxidation in plant tissues measured through MDA content in short 7 days 100 µM treatment. Antioxidant enzyme studies showed that inoculation of control plants enhanced APX, SOD and CAT activities after 30 days in shoots and SOD, APX, SOD, GPOX in roots. Application of 50 µM CdCl₂ stimulated all enzymes in shoots and decreased SOD and CAT activities in roots. Moreover, 100 µM of CdCl₂ increased SOD, APX, CAT and GPOX activities in shoots and increased significantly CAT activity in roots. Metal accumulation depended on Cd concentration, plant organ and time of treatment. Furthermore, the inoculation enhanced Cd uptake in roots by 20% in all treatments. The cultivation of this symbiosis in Cd contaminated soil or in heavy metal hydroponically treated medium, showed that inoculation improved plant biomass and increased Cd uptake especially in roots. Therefore, the present study established that co-inoculation of S. coronaria by a specific consortium of heavy metal resistant PGPB formed a symbiotic system useful for soil phytostabilization.     

H2O2 Involvement in Polyamine-Induced Cell Death in Tobacco Leaf Discs

The response of tobacco (Nicotiana tabacum L.) wild-type SR1 leaf discs in terms of reactive oxygen species (ROS) formation and cell death occurrence was evaluated after exposure to the polyamines (PAs) putrescine (Put), spermidine (Spd), and spermine (Spm). Although NADPH oxidase-like enzyme activity was inhibited by all PAs at 3 or 21 h of treatment, H₂O₂ content increased significantly in a time- and concentration-dependent manner, suggesting that H₂O₂ accumulation was linked to the activity of other ROS-generating enzymes. Polyamine oxidase (PAO) activity, which increased markedly upon application of Spd or Spm, is a prime candidate for the increased H₂O₂ accumulation. Except for 0.1 mM Put, which maintained guaiacol peroxidase (GPOX) and catalase (CAT) activities at the same level as the control, the other PA treatments decreased CAT, ascorbate peroxidase, and GPOX activities at 21 h, contributing to the H₂O₂ increase. Esterase activity and Evans blue staining, two cell death parameters, were negatively affected at 3 h of treatment with 1 mM Spd and with both concentrations of Spm, whereas at 21 h there was an increase in cell death with both concentrations of the three PAs, except for 0.1 mM Put, which did not alter those parameters. The expression of the senescence-associated cysteine protease gene CP1 was measured to monitor senescence, a physiological cell death process. Application of all PAs increased the expression of the gene, except for 0.1 mM Put, which decreased its expression at 21 h. This result was in agreement with the prevention of cell death exerted by Put and evidenced by Evans blue staining, esterase activity, and electrolyte release.     

Evaluation of heme oxygenase 1 (HO 1) in Cd and Ni induced cytotoxicity and crosstalk with ROS quenching enzymes in two to four leaf stage seedlings of <Emphasis Type="Italic">Vigna radiata</Emphasis>

Research on heme oxygenase in plants has received consideration in recent years due to its several roles in development, defense, and metabolism during various environmental stresses. In the current investigation, the role of heme oxygenase (HO) 1 was evaluated in reducing heavy metal (Cd and Ni) uptake and alleviating Cd and Ni toxicity effects in the hydroponically grown seedlings of Vigna radiata var. PDM 54. Seedlings were subjected to Cd- and Ni-induced oxidative stress independently at different concentrations ranging from 10 to 100 μM. After 96 h (fourth day) of treatment, the stressed plants were harvested to study the cellular homeostasis and detoxification mechanism by examining the growth, stress parameters (LPX, H₂O₂ content), and non-enzymatic and enzymatic parameters (ascorbate peroxidase (APX), guaicol peroxidase (GPX), and catalase (CAT)) including HO 1. At 50 μM CdCl₂ and 60 μM NiSO₄, HO 1 activity was found to be highest in leaves which were 1.39 and 1.16-fold, respectively. The greatest HO 1 activity was reflected from the reduction of H₂O₂ content at these metal concentrations (50 μM CdCl₂ and 60 μM NiSO₄) which is correlated with the increasing activity of other antioxidant enzymes (CAT, APX). Thus, HO 1 works within a group that generates the defense machinery for the plant’s survival by scavenging ROS which is confirmed by a time-dependent study. Hence, it is concluded that seedlings of V. radiata were more tolerant towards metal-induced oxidative stress in which HO 1 is localized in its residential area (plastids).     

A Study on Cadmium Phytoremediation Potential of Indian Mustard,Brassica juncea

The objective of this study was to investigate Cd phytoremediation ability of Indian mustard, Brassica juncea. The study was conducted with 25, 50, 100, 200 and 400 mg Kg^?1 CdCl₂ in laboratory for 21 days and Cd concentrations in the root, shoot and leaf tissues were estimated by atomic absorption spectroscopy. The plant showed high Cd tolerance of up to 400 mg Kg^?1 but there was a general trend of decline in the root and shoot length, tissue biomass, leaf chlorophyll and carotenoid contents. The tolerance index (TI) of plants were calculated taking both root and shoot lengths as variables. The maximum tolerance (TI _shoot = 87.4 % and TI _root = 89.6 %) to Cd toxicity was observed at 25 mg Kg^?1, which progressively decreased with increase in dose. The highest shoot (10791 μg g^?1 dry wt) and root (9602 μg g^?1 dry wt) Cd accumulation was achieved at 200 mg kg^?1 Cd treatment and the maximum leaf Cd accumulation was 10071.6 μg g^?1 dry wt achieved at 100 mg Kg^?1 Cd, after 21 days of treatment. The enrichment coefficient and root to shoot translocation factor were calculated, which, pointed towards the suitability of Indian mustard for removing Cd from soil.     

In vitro induction of tetraploid <Emphasis Type="Italic">Ziziphus jujuba</Emphasis> Mill. var. <Emphasis Type="Italic">spinosa</Emphasis> plants from leaf explants

The genetic manipulation of Capsicum has been unsuccessful, and a large bottleneck to transferring the desired genes is due to the difficulty in regenerating whole plants through tissue culture because of its highly recalcitrant and high genotype specificity. This study aimed to investigate and establish rapid shoot regeneration from the proximal ends of the leaves of Capsicum frutescens KT-OC and BOX-RUB varieties. A maximum of 8–10 shoot buds were obtained from the margins of the proximal portion of a cotyledonary leaf explant of C. frutescens variety KT-OC on medium I containing 44.44 µM 6-benzylaminopurine (BA), 5.71 µM indole-3-acetic acid (IAA), 10 µM silver nitrate (AgNO₃) and 1.98 mg L^?1 2-(N-morpholine) ethane sulphonic acid within 4 weeks of incubation, of which 60% of explants responded in terms of shoot buds. Petiole explants (40%) cultured on the same medium produced 2–4 shoots per explant from the distal portion. The cut portions of the cotyledonary leaf proximal portions responded well to shoot bud formation in the presence of 22.20 µM BA and 14.68 µM phenyl acetic acid (PAA), wherein 100% of explants responded in terms of shoot bud formation, with an average of 10?±?1.7 and 8?±?1.9 shoot buds per explant in KT-OC and BOX-RUB varieties, respectively. The differentiated shoots grew well and proliferated in the presence of 14.68 µM PAA?+?22.20 µM BA and 10 µM AgNO₃. Shoot elongation was obtained in presence of 1.44 µM gibberellic acid (GA₃) and 10 µM AgNO₃. These shoots were rooted on plant growth regulator-free half-strength MS medium and upon hardening; field survival rate was 70%. This reproducible regeneration method for C. frutescens, especially the Indian high pungent variety, from proximal portion of cotyledonary leaf and petiole explants, can be used for biotechnological improvement.     

Iron plaque formation in the roots of Pistia stratiotes L.: importance in phytoremediation of cadmium

Aquatic macrophytes play an important role in the removal of toxic metals from wastewater. Therefore, the induction of Fe plaque on the roots, and its consequences on Cd tolerance investigated in an aquatic macrophyte Pistia stratiotes L. The presence of Fe²⁺ ion but not Fe³⁺ resulted in Fe plaque formation. Induction of Fe plaque decreased Ca and increased K and Fe accumulations in the root. Plaque formed plants had accumulated less Cd until 50.0?µM CdCl₂ treatments because plaque acted as a barrier to Cd exposure. However, at higher concentrations (500.0?µM CdCl₂), plaque formed plants contained more Cd in the roots. Cadmium inducible ion leakage in the root and lowering of the photosynthetic pigment content were less in plants with a plaque. Stretching of aromatic carbonyl groups and alkyl groups among plaque formed plants upon Cd treatments indicated the putative role of phenolics in Cd detoxification.     

Effects of Cadmium on Antioxidant Enzyme Activities in Sugar Cane

Sugar cane (Saccharum officinarum L. cv. Copersucar SP80-3280) seedlings were grown in nutrient solution with varying concentrations (0, 2 and 5 mM) of cadmium chloride for 96 h. Leaves were analysed for catalase (CAT), glutathione reductase (GR) and superoxide dismutase (SOD) activities. Although a clear effect of CdCl₂ on plant growth was observed, the activity of SOD was not altered significantly. However, the CAT activity decreased as the concentration of CdCl₂ increased. GR exhibits a significant increase in activity at 2 and 5 mM CdCl₂. CAT and SOD isoenzymes were further characterised by analysis in non-denaturing PAGE. Activity staining for SOD revealed up to seven isoenzymes in untreated control and 2 mM CdCl₂ treated plants, corresponding to Cu/Zn-SOD isoenzymes. At 5 mM CdCl₂, only six Cu/Zn-SOD isoenzymes were observed. No Fe-SOD and Mn-SOD isoenzymes were detected. For CAT, one band of activity was observed.     

Leaf responses to iron nutrition and low cadmium in peanut: anatomical properties in relation to gas exchange

Aims

This study evaluated how iron nutrition affect leaf anatomical and photosynthetic responses to low cadmium and its accumulation in peanut plants.

Methods

Seedlings were treated with Cd (0 and 0.2 μM CdCl₂) and Fe (0, 10, 25, 50 or 100 μM EDTA-Na₂Fe) in hydroponic culture.

Results

Cadmium accumulation is highest in Fe-deficient plants, and dramatically decreased with increasing Fe supply. The biomass, gas exchange, and reflectance indices were highest at 25 μM Fe²⁺ treatments, indicating the concentration is favorable for the growth of peanut plants. Both Fe deficiency and Cd exposure impair photosynthesis and reduce reflectance indices. However, they show different effects on leaf anatomical traits. Fe deficiency induces more and smaller stomata in the leaf surface, but does not affect the inner structure. Low Cd results in a thicker lamina with smaller stomata, thicker palisade and spongy tissues, and lower palisade to spongy thickness ratio. The stomatal length and length/width ratio in the upper epidermis, spongy tissue thickness, and palisade to spongy thickness ratio were closely correlated with net photosynthetic rate, stomatal conductance, and transpiration rate.

Conclusions

Cd accumulation rather than Fe deficiency alters leaf anatomy that may increase water use efficiency but inhibit photosynthesis.     

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.     

Grafting of watermelon (Citrullus lanatus cv. Mahbubi) onto different squash rootstocks as a means to minimize cadmium toxicity

To test the possibility that using appropriate rootstocks could improve the tolerance of watermelon to cadmium (Cd) toxicity, a greenhouse experiment was conducted to determine growth and antioxidant activities of watermelons, either nongrafted or grafted onto summer squash and winter squash. We provided nutrient solutions having four levels (0, 50, 100, and 200 μM) of cadmium to treat the plants. Shoot and root biomass reduction were significantly lower in summer squash rootstock-grafted watermelon than winter squash rootstock-grafted and nongrafted watermelons. Cadmium induced a smaller decrease in leaf area index in grafted watermelons compared with nongrafted plants. The Cd- related reductions in chlorophyll content and efficiency of photosynthesis were more severe in nongrafted watermelons compared with dose grafted onto summer squash. Cd accumulation in shoot at the highest dose (200 µM) of CdCl₂ was significantly lower (19.76 mg/kg) in summer squash rootstock-grafted watermelon compared with winter squash rootstock-grafted (37.58 mg/kg) and nongrafted watermelon (72.12 mg/kg). H₂O₂, MDA production and electrolyte leakage of summer squash rootstock-grafted watermelon showed less increase, which was associated with a significant increase in the activities of antioxidant. The improved crop performance of grafted watermelons was attributed to their strong capacity to inhibit Cd accumulation in the aerial parts.     

Enhancement of phenylpropanoid enzymes and lignin in Phalaenopsis orchid and their influence on plant acclimatisation at different levels of photosynthetic photon flux

Effects of three levels of photosynthetic photon flux (PPF: 60, 160 and 300 μmol m⁻²s⁻¹) were investigated in one-month-old Phalaenopsis plantlets acclimatised ex vitro. Optimal growth, chlorophyll and carotenoid concentations, and a high carotenoid:chlorophyll a ratio were obtained at 160 μmol m⁻²s⁻¹, while net CO₂ assimilation (A), stomatal conductance (g), transpiration rate (E) and leaf temperature peaked at 300 μmol m⁻²s⁻¹, indicating the ability of the plants to grow ex vitro. Adverse effects of the highest PPF were reflected in loss of chlorophyll, biomass, non-protein thiol and cysteine, but increased proline. After acclimatisation, glucose-6-phosphate dehydrogenase, shikimate dehydrogenase, phenylalanine ammonia-lyase (PAL) and cinnamyl alcohol dehydrogenase (CAD) increased, as did lignin. Peroxidases (POD), which play an important role in lignin synthesis, were induced in acclimatised plants. Polyphenol oxidase (PPO) and β-glucosidase (β-GS) activities increased to a maximum in acclimatised plants at 300 μmol m⁻²s⁻¹. A positive correlation between PAL, CAD activity and lignin concentration was observed, especially at 160 and 300 μmol m⁻²s⁻¹. The study concludes that enhancement of lignin biosynthesis probably not only adds rigidity to plant cell walls but also induces defence against radiation stress. A PPF of 160 μmol m⁻²s⁻¹was suitable for acclimatisation when plants were transferred from in vitro conditions.     

Combination of site-specific recombination and a conditional selective marker gene allows for the production of marker-free tobacco plants

We have designed an innovative construct (pX6-DAO1) combining the chemical inducible Cre-LoxP system and the conditional selectable marker gene dao1 to obtain marker-free transgenic tobacco plants. Nicotiana tabaccum transgenic lines were regenerated on medium with 6 mM d-alanine. The DNA site-specific recombination was controlled by the inducer ß-estradiol. Regeneration on medium containing 5 μM ß-estradiol and 8 mM d-valine was not obtained. However, leaf disks from all transgenic lines regenerated in the presence of ß-estradiol, although only 9.4 % of regenerated buds developed solid marker-free shoots. Partial recombination was found in 71.7 % of buds, and no recombination was detected in only 18.9 % of buds. Nevertheless, when leaf disks from chimeric shoots were cultured in medium with 8 mM d-valine, only marker-free buds regenerated, and no partial recombinants were detected. Similarly, marker-free plants were produced from T₂ seeds, obtained from chimeric ß-estradiol-induced T₁ plants, with 100 % efficiency in selective d-valine medium.     

Influence of CdCl2 and CdSO4 supplementation on Cd distribution and ligand environment in leaves of the Cd hyperaccumulator Noccaea (Thlaspi) praecox

Background and aims

The aim was to investigate whether different Cd salts in the nutrient solution of the Cd/Zn hyperaccumulator Noccaea (Thlaspi) praecox alter leaf Cd distribution and Cd ligand environment, and plant fitness.

Methods

Plants were grown for 8 weeks with 100/300 μM CdCl₂ or CdSO₄. Leaf biomass, and total chlorophyll, anthocyanin, Cd, Cl, S and P concentrations were monitored. Cd localisation and ligand environment in leaves were analysed using quantitative synchrotron-based micro-X-ray fluorescence imaging, and Cd K-edge X-ray absorption fine structure and Cd L₃-edge micro-X-ray absorption near-edge structure measurements.

Results

Cd uptake and plant fitness were comparable for CdCl₂ and CdSO₄ treatments, and depended on applied Cd concentration. In all treatments, Cd preferentially accumulated with high concentrations of Cl in vacuoles of large vacuolarised epidermal cells, bound mainly to oxygen-based (O)-ligands. In the mesophyll of CdCl₂? treated plants, Cd was preferentially sequestered in vacuoles, while for CdSO₄, Cd accumulated preferentially in the apoplast. In the symplast, O-ligands increased with increasing Cd concentrations; in the apoplast, sulphur-based (S)-ligands prevailed.

Conclusions

Cd partitioning between leaf mesophyll apoplast and symplast and the Cd ligand environment in N. praecox depend on the Cd salt type and concentration added to the nutrient solution.     

Cadmium tolerance in <Emphasis Type="Italic">Schinus molle</Emphasis> trees is modulated by enhanced leaf anatomy and photosynthesis

Key message

Low concentrations of cadmium cause anatomical responses in leaf chlorenchyma enhancing Schinus molle photosynthesis and tolerance.

Abstract

This work is aimed to evaluate the effects of cadmium (Cd) on leaf anatomy and photosynthesis in Schinus molle, a species that can cope with harsh environments. Seven-month-old S. molle plants were exposed over 90 days to varying Cd concentrations (0, 10, 20, 50, 125 or 250 µM using Cd(NO₃)₂ as the Cd source). The plants were placed in vases containing washed sand and vermiculite as the substrate and nutrient solution. Throughout the experiment, the substrate was maintained at field capacity, and the nutrient solution was replaced at 15-day intervals. After 90 days, leaves were collected and processed for anatomical analysis using typical plant microtechniques. In addition, plant growth, photosynthesis, chlorophyll content and A/Ci curve were evaluated using an infrared gas analyzer. S. molle growth was not affected by Cd. Lower Cd concentrations (10 and 20 µM) resulted in greater net photosynthesis, stomatal conductance and density, Vcmax, Jmax and mesophyll thickness. However, Cd concentrations of 50 µM or greater resulted in a reduction of most of the evaluated characteristics to levels close to control. All of the tested Cd concentrations resulted in reduced chlorophyll content and stomatal size. Therefore, the effect of Cd in a tolerant species such as S. molle is concentration dependent, and at low Cd concentrations, these plants can cope with the toxicity by adjusting leaf structure and function.

     

Fungicide resistance of Botrytis cinerea in tomato greenhouses in the Canary Islands and effectiveness of non-chemical treatments against gray mold

Tomato greenhouses in the Canary Islands, Spain, were surveyed to estimate frequencies of resistance to benzimidazoles, dicarboximides, anilinopyrimidines and N-phenylcarbamates in Botrytis cinerea. Resistance to carbendazim, iprodione, pyrimethanil and diethofencarb was found in 74.2, 86.4, 28.8 and 31.8 % of isolates, respectively. Benzimidazole- and anilinopyrimide-resistant isolates were highly resistant, showing EC₅₀ values above 500 µg/ml carbendazim and a mean EC₅₀ value of 28.42 µg/ml pyrimethanil, respectively. By contrast, a low level of resistance was observed among dicarboximide-resistant isolates (mean EC₅₀ value of 1.81 µg/ml iprodione). Phenotypes with double resistance to carbendazim and iprodione, and triple resistance to carbendazim, iprodione and pyrimethanil were the most common, occurring in 36.4 and 28.8 % of isolates. The surveyed greenhouses had never been treated with fenhexamid and Signum? (pre-packed mixture of boscalid and pyraclostrobin), and baseline sensitivities of B. cinerea isolates to these fungicides were determined. The EC₅₀ values were within the range of 0.009–0.795 µg/ml fenhexamid and of 0.014–0.48 µg/ml Signum. In addition, available formulations based on elicitors of plant defense response and biocontrol agents were evaluated against B. cinerea in tomato plants under semi-controlled greenhouse conditions, the yeast Candida sake CPA-1 being able to reduce gray mold significantly when it was applied on petiole wounds and the plants were inoculated 24 h later. Likewise, C. sake was effective against B. cinerea in harvested tomato fruits, yeast-treated tomatoes showed a 70.66 and 30.31 % reduction in the diameters of decay lesions compared with controls after 10 days of storage at 20 and 9 °C, respectively.     

Cadmium induces senescence symptoms in leaf peroxisomes of pea plants

The effect of growing pea (Pisum sativum L.) plants with a toxic CdCl₂ concentration (50 µm ) on the metabolism and proteolytic activity of leaf peroxisomes was studied. In peroxisomes purified from plants treated with cadmium, an increase in the total protein concentration and in the activity and protein level of the photorespiratory enzyme glycolate oxidase was found. The glyoxylate cycle enzymes, malate synthase and isocitrate lyase, whose activity is normally very low in leaf peroxisomes, were enhanced by Cd treatment. The activity of the endogenous proteases of leaf peroxisomes was determined. Two leucine‐aminopeptidase isozymes (AP1‐AP2) were detected, and their activity was slightly higher in Cd‐treated plants. Five endopeptidases (EP1‐EP5) were present in pea leaf peroxisomes, and in plants grown with Cd the activity of isozymes EP1‐EP4 was increased. The ultrastructural analysis of pea leaves showed that Cd produced a disorganization of the chloroplast structure, with an increase in the number of plastoglobuli, and the formation of vesicles in the vacuoles. Taken together, these results indicate that Cd induces senescence symptoms in leaf peroxisomes, and probably a metabolic transition of leaf peroxisomes into glyoxysomes, and suggest that the peroxisomal proteases could participate in the metabolic changes produced by Cd.     

Susceptibility of Asian citrus psyllid, <Emphasis Type="Italic">Diaphorina citri</Emphasis> (Hemiptera: Liviidae), to the insecticide afidopyropen: a new and potent modulator of insect transient receptor potential channels

A relatively new insecticide chemistry for controlling sucking insects, afidopyropen, was investigated for toxicity against Asian citrus psyllid, Diaphorina citri Kuwayama (Hemiptera: Liviidae). We evaluated the mortality of D. citri eggs, nymphs, and adults treated with afidopyropen using both laboratory-reared and field populations. We also quantified the effects of sublethal doses of afidopyropen on D. citri feeding, host choice selection, and fecundity. For laboratory susceptible adults, the contact LC₅₀, topical application LD₅₀, and leaf dip LC₅₀ were 2.13, 2.00, and 3.08 ng/µL, respectively. For adults collected from a commercially managed citrus grove in Florida, the contact LC₅₀, topical application LD₅₀, and leaf dip LC₅₀ were 1.37, 1.92, and 4.89 ng/µL, respectively. Egg hatch was significantly reduced following exposure to afidopyropen at 100 ng/µL. Furthermore, afidopyropen reduced D. citri nymph survival and adult emergence at concentrations ranging between 0.01 and 100 ng/µL. Diaphorina citri adult feeding decreased on citrus leaves treated with afidopyropen in a concentration-dependent manner as measured indirectly by honeydew excretion, and appeared almost completely inhibited after treatment with 10 and 100 ng/µL solutions of afidopyropen. In choice tests, significantly fewer D. citri adults settled on afidopyropen-treated plants than on control plants at 24, 48, and 72 h after release, with no differences in settling between males and females. Afidopyropen reduced the fecundity of D. citri in a concentration-dependent manner. Collectively, the results suggest that afidopyropen could contribute to the integrated management of D. citri and may therefore be useful in rotational programs to improve resistance management.     

Effect of Electron Donor to Sulfate Ratio on Mercury Methylation in Floodplain Sediments under Saturated Flow Conditions

A column transport experiment was conducted to examine the release and methylation of Hg using Hg contaminated sediment from the floodplain of the South River near Waynesboro, Virginia. Three input solutions were sequentially introduced into the column. Input 1 was unamended South River water, Input 2 was river water amended with 100 mg L^?1 SO₄ and 3600 mg L^?1 lactate, and Input 3 was river water amended with 500 mg L^?1 SO₄ and 340 mg L^?1 lactate. During the first stage of the experiment (Input 1) the effluent Hg concentration was initially 4 µg L^?1 and peaked at 21 µg L^?1 and after 21 pore volumes stabilized at 13 µg L^?1. During the second stage, at high lactate to SO₄ ratios, elevated concentrations of acetic and propionic acids were detected, indicating that fermentative bacteria were dominant. During the third stage, at high SO₄ to lactate ratios, a decrease in SO₄ and an increase in H₂S concentrations were detected in the column effluent indicating that SO₄ reduction was occurring. Concentrations of methyl Hg (MeHg) in the effluent were variable over the duration of the experiment. During the first phase, concentrations of MeHg remained <3.3 ng L^?1. During the fermentative stage, concentrations of MeHg increased to a maximum value of 32 ng L^?1, and during the sulfate-reducing stage to a maximum value of 266 ng L^?1. When the column was deconstructed both molecular and cultural techniques indicated that sulfate reducing bacteria were most dominant near the influent port. These results indicate that the formation of MeHg in the sediment is not limited by the availability of Hg and that the bacterial community that contributes to mercury methylation can respond quickly to changes in the abundances of electron donors and acceptors.     

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.