Occurrence and fate of the phytotoxin juglone in alley soils under black walnut trees

Indole and quinolizidine alkaloids from blue lupin leach to agricultural drainage water

Phytotoxins are produced in plants including agricultural crops. Lupins and other plants of the Fabaceae family produce toxic alkaloids. These alkaloids have been studied in food and feed, however, the environmental fate of alkaloids produced by cultivated lupins is largely unknown. Therefore, we conducted an agricultural field experiment to investigate the occurrence of indole and quinolizidine alkaloids in lupin plant tissues, soil, soil pore water and in drainage water. During the field experiment, alkaloids were regularly quantified (median concentrations) in lupin (13-8.7 × 10³ ng/g dry weight (dw)), and topsoils at depth 0-5 cm (0.1-10 ng/g dw), and depth 15-30 cm (0.2-8.5 ng/g dw), soil pore water (0.2-7.5 ng/L) and drainage water samples (0.4-18 ng/L). Lupanine was the dominant alkaloid in all collected samples. Cumulative amounts of alkaloids emitted via drainage water were around 0.1-11 mg/ha for individual alkaloids over one growing season. The total cumulative amount of alkaloid in drainage water was 14 mg/ha, which is a very small amount compared to the mass of alkaloid in the lupin biomass (11 kg/ha) and soil (0.02 kg/ha). Nearly half of the alkaloids were exported in the drainage water during high flow events, indicating that alkaloids transport preferentially via macropores. These findings indicate that drainage from lupin cultivated areas contribute to surface water contamination. The environmental and ecotoxicological relevance of alkaloids as newly identified aquatic micropollutants in areas with agricultural activities have yet to be assessed.

Kinetic solvent viscosity effects uncover an internal isomerization of the enzyme-substrate complex in Pseudomonas aeruginosa PAO1 NADH:Quinone oxidoreductase

NAD(P)H:quinone oxidoreductases (NQOs) play an essential protective role as antioxidants in the detoxification of quinones in both Prokaryotes and Eukaryotes. NQO from Pseudomonas aeruginosa PAO1 uses FMN to catalyze the two-electron reduction of various quinones with NADH. In this study, steady-state kinetics, kinetic solvent viscosity effects, and rapid reaction kinetics were used to determine which kinetic steps control the overall turnover of the enzyme with benzoquinone or juglone. The rate constant for flavin reduction (k_red) at pH 6.0 was 12.9 ± 0.3 s^-1, and the K_d for NADH was at least an order of magnitude lower than 90 μM. With benzoquinone, the k_cat value was 11.7 ± 0.3 s^-1, consistent with flavin reduction being almost entirely rate-limiting for overall turnover. With juglone, a k_cat value of 10.0 ± 0.5 s^-1 was recorded. The normalized plot of the relative solvent viscosity effects on the k_cat values established that hydride transfer from NADH to the FMN and quinol product release, with a calculated rate constant (k_P-rel) of 52 s^-1, are partially rate-limiting for the overall turnover of NQO. Kinetic solvent viscosity effects with glucose or sucrose revealed a hyperbolic dependence on the k_cat and k_cat/K_m values with benzoquinone or juglone, respectively, consistent with the presence of a solvent-sensitive internal isomerization of the enzyme-substrate complex (ES). The data demonstrate opposing effects of benzoquinone and juglone on the equilibrium of the NQO ES isomerization with glucose or sucrose. Thus, our study demonstrates how quinol substrate properties alter the equilibrium of NQO ES isomerization.

Host plant stimuli effects on survival and duration of dormancy of Rhagoletis zoqui, Rhagoletis completa (Diptera: Tephritidae) and associated parasitoids

Tephritid fruit flies in the genus Rhagoletis bridge between predictable periods of fruit availability by becoming dormant. To cope with acyclic unpredictable events (e.g., frost, mast seeding, etc), a proportion of the population can undergo prolonged dormancy. In the case of walnut infesting Rhagoletis, host plant-derived cues such as juglone soil concentration vary seasonally in predictable patterns. Here, we examined the effects of host plant parts and derived compounds on emergence rates and dormancy duration of Rhagoletis completa (Cresson), Rhagoletis zoqui (Bush) (Diptera: Tephritidae), and associated parasitoids. Pupae of both species were exposed to walnut leaves, fruit, or fruit and leaves and compared to a control. In a second experiment, R. zoqui were exposed to 10 mg l-1 of juglone applied to pupation medium during four consecutive 4-week time periods under variable combinations of temperature and frequency of exposure. Overall, the presence of fruit resulted in greater overwintering survival of R. completa but had no effect on the duration of dormancy of either fly species. Application of juglone over two consecutive periods produced greater mortality of R. zoqui than the control. Three parasitoid species emerged from R. completa and one from R. zoqui. Duration of dormancy for parasitoids was longer than that of fly hosts. Regardless of treatment, 13.3-18.4% of R. completa pupae and 1.3-2.8% R. zoqui engaged in prolonged (>year) dormancy. Our results indicate that host plant derived cues have little or no effect on survival and duration of dormancy of walnut infesting Rhagoletis, and at the tested concentration juglone is toxic to R. zoqui pupae. Testing the effect of juglone at lower concentrations is necessary to rule out its role as an environmental cue for regulation of dormancy. So far, host plant fruiting phenology appears to play a greater role than host plant derived cues in selecting for fly eclosion times.

Apple tree adaptation to shade in agroforestry: an architectural approach

PREMISE

The expression of shade adaptation traits is expected to be stronger in low light and can be detrimental to flowering and yield. Our study focused on the expression of shade adaptation traits of apple trees (Malus domestica Borkh. 'Dalinette') in an agroforestry system.

METHODS

The architecture of 45 apple trees in their third and fourth year was extensively described and analyzed at the tree scale and compared depending on the light quantity received during the growing season. Flower cluster phenology and the relation between leaf area and floral initiation were also investigated.

RESULTS

The number of growing shoots and the leaf area were reduced by shade even if specific leaf area increased with increasing shade. Shade did not modify primary growth but did decrease secondary growth, so that apple tree shoots in shade were slender, with a lower taper and reduced number and proportion of flower clusters. The correlation between floral initiation and leaf area was high both in full and moderate light but not for apple trees in low light. Shade did not impact the date of bud burst and the early phenological stages of flower clusters, but it reduced the number of days at full bloom.

CONCLUSIONS

Our results suggest that while the architecture of apple trees is modified by a reduction in light intensity, it is not until a reduction of 65% that the capability to produce fruit is impeded. These results could help optimize the design of apple-tree-based agroforestry systems.

Mitochondrial hydrogen peroxide positively regulates neuropeptide secretion during diet-induced activation of the oxidative stress response

Mitochondria play a pivotal role in the generation of signals coupling metabolism with neurotransmitter release, but a role for mitochondrial-produced ROS in regulating neurosecretion has not been described. Here we show that endogenously produced hydrogen peroxide originating from axonal mitochondria (mtH2O2) functions as a signaling cue to selectively regulate the secretion of a FMRFamide-related neuropeptide (FLP-1) from a pair of interneurons (AIY) in C. elegans. We show that pharmacological or genetic manipulations that increase mtH2O2 levels lead to increased FLP-1 secretion that is dependent upon ROS dismutation, mitochondrial calcium influx, and cysteine sulfenylation of the calcium-independent PKC family member PKC-1. mtH2O2-induced FLP-1 secretion activates the oxidative stress response transcription factor SKN-1/Nrf2 in distal tissues and protects animals from ROS-mediated toxicity. mtH2O2 levels in AIY neurons, FLP-1 secretion and SKN-1 activity are rapidly and reversibly regulated by exposing animals to different bacterial food sources. These results reveal a previously unreported role for mtH2O2 in linking diet-induced changes in mitochondrial homeostasis with neuropeptide secretion.

…Fell Upas Sits, the Hydra-Tree of Death †, or the Phytotoxicity of Trees

The use of natural products that can serve as natural herbicides and insecticides is a promising direction because of their greater safety for humans and environment. Secondary metabolites of plants that are toxic to plants and insects-allelochemicals-can be used as such products. Woody plants can produce allelochemicals, but they are studied much less than herbaceous species. Meanwhile, there is a problem of interaction of woody species with neighboring plants in the process of introduction or invasion, co-cultivation with agricultural crops (agroforestry) or in plantation forestry (multiclonal or multispecies plantations). This review describes woody plants with the greatest allelopathic potential, allelochemicals derived from them, and the prospects for their use as biopesticides. In addition, the achievement of and the prospects for the use of biotechnology methods in relation to the allelopathy of woody plants are presented and discussed.

Comprehensive Toxic Plants-Phytotoxins Database and Its Application in Assessing Aquatic Micropollution Potential

The production of toxic plant secondary metabolites (phytotoxins) for defense is a widespread phenomenon in the plant kingdom and is even present in agricultural crops. These phytotoxins may have similar characteristics to anthropogenic micropollutants in terms of persistence and toxicity. However, they are only rarely included in environmental risk assessments, partly because a systematic overview of phytotoxins is missing. Here, we present a newly developed, freely available database, Toxic Plants-PhytoToxins (TPPT), containing 1586 phytotoxins of potential ecotoxicological relevance in Central Europe linked to 844 plant species. Our database summarizes phytotoxin patterns in plant species and provides detailed biological and chemical information as well as in silico estimated properties. Using the database, we evaluated phytotoxins regarding occurrence, approximated from the frequencies of Swiss plant species; environmental behavior based on aquatic persistence and mobility; and toxicity. The assessment showed that over 34% of all phytotoxins are potential aquatic micropollutants and should be included in environmental investigations.

Root order-based traits of Manchurian walnut & larch and their plasticity under interspecific competition

Manchurian walnut and larch are key timber species of northeast China but information on (fine) root traits of both species is scarce. Plasticity of root traits in mixed plantations has been studied rarely although this could give important insights into mechanisms of root competition. This study examined root traits by branching order in 30-yr-old monocultures and their plasticity in mixed plantations. In monocultures, Manchurian walnut and larch differed in key fine root traits. Larch roots hold more absorptive root orders, larger diameter and lower specific root length/area. Walnut root orders featured greater cortex:stele ratios, N-concentrations and respiration rates. Under interspecific competition, the proportion of walnut root tips increased, the biomass/length of larch root orders 1-3 decreased. Larch possessed a greater morphological and anatomical plasticity of terminal root orders than walnut. Mycorrhizal colonization rates of walnut were reduced. Both species differed fundamentally in their fine root properties. Absorptive fine root orders reacted plastic under interspecific competition while traits of higher root orders remained unchanged. In mixture, larch roots possessed a greater plasticity in traits related to resource uptake (efficiency) than walnut roots whose reaction norm is suggested to be predominantly based on interference competition via juglone exudation.

Toxicity of the bionematicide 1,4-naphthoquinone on non-target soil organisms

The main goal of the present study was to evaluate the ecotoxicological effects of 1,4-naphthoquinone (1,4-NTQ), a natural-origin compound presenting nematicidal activity, that can be obtained from walnut husk, in plants and soil invertebrates, including non-target soil nematode communities. This research was part of an ongoing project that aims to develop environmentally-friendly nematicides obtained from agricultural residues. The battery of ISO tests included emergence and growth of corn (Zea mays) and rape (Brassica napus); avoidance with the earthworm Eisenia andrei and the collembolan Folsomia candida; and reproduction with the previous species plus the enchytraeid Enchytraeus crypticus. A novel soil nematode community assay was also performed. ISO tests and nematode assays were conducted using a natural uncontaminated soil that was spiked with a range of 1,4-NTQ concentrations. Toxicity of 1,4-NTQ was found for all test-species and the most sensitive were F. candida and E. andrei. After 7 days of exposure to 1,4-NTQ, nematode abundance decreased along the concentration gradient, and a partial recovery was observed after 14 days (1,4-NTQ <48 mg kg^-1 soil). The number of nematode families consistently decreased in both periods. Overall, results indicate that a 1,4-NTQ concentration of <20 mg kg^-1 could be environmentally safe but preliminary data suggest that it might be ineffective for the target-nematodes, root-knot nematodes, Meloidogyne spp., and root-lesion nematodes, Pratylenchus spp. In addition, if higher dosages of 1,4-NTQ bionematicide are necessary, the potential recovery of non-target organisms under real field scenarios also needs to be assessed.

Inhibition of the oxidative stress response by heat stress in Caenorhabditis elegans

It has long been recognized that simultaneous exposure to heat stress and oxidative stress shows a synergistic interaction that reduces organismal fitness, but relatively little is known about the mechanisms underlying this interaction. We investigated the role of molecular stress responses in driving this synergistic interaction using the nematode Caenorhabditis elegans. To induce oxidative stress, we used the pro-oxidant compounds acrylamide, paraquat, and juglone. As expected, we found that heat stress and oxidative stress interact synergistically to reduce survival. Compared to exposure to each stressor alone, during simultaneous, sub-lethal exposure to heat stress and oxidative stress the normal induction of key oxidative stress response (OxSR) genes was generally inhibited while the induction of key heat shock response (HSR) genes was not. Genetically activating the SKN-1 dependent OxSR increased a marker for protein aggregation and decreased whole-worm survival during heat stress alone, with the latter being independent of HSF-1. In contrast, inactivating the HSR by HSF-1 knockdown, which would be expected to decrease basal heat shock protein expression, increased survival during oxidative stress alone compared to wild- type worms. Taken together, these data suggest that in C. elegans the HSR and OxSR cannot be simultaneously activated to the same extent that each can be activated during a single stressor exposure. We conclude that the observed synergistic reduction in survival during combined exposure to heat stress and oxidative stress is due, at least in part, to inhibition of the OxSR during activation of the HSR.

Effect of Pin1 inhibitor juglone on proliferation, migration and angiogenic ability of breast cancer cell line MCF7Adr

This study aimed to evaluate the effects of Pin1 inhibitor Juglone on proliferation, migration and the angiogenic ability of breast cancer cell line MCF7Adr. MCF7Adr cells were cultured and separately treated with Pin1 inhibitor Juglone (treatment group) and DMEM without drug (control group). The cell cycle was examined by flow cytometry. Cell migration was measured by wound-healing assay. Cyclin E protein content was detected by Western blotting. The angiogenesis factor vascular endothelial growth factor (VEGF) in cell media was determined by enzyme linked immunosorbent assay. The results showed that the percentage of cells in G2/M phase in treatment group was significantly higher than that in control group (25.5% vs. 10.1%, P<0.05), and that in G0/G1 phase and S stage in treatment group was significantly lower than that in control group (40.5% vs. 48.2%, and 33.7% vs. 41.7%, P<0.05). Cyclin E protein content in treatment group was significantly lower than that in control group (39.2 ± 7.4 vs. 100 ± 23.1, P<0.05). (A0-A24)/A0 value in treatment group was significantly lower than that in control group (23.9 ± 3.8 vs. 100 ± 14.4, P<0.05). VEGF-A, -B, and -C contents in cell media of treatment group were significantly lower than those in control group (P<0.05). It was suggested that Pin1 inhibitor Juglone can effectively inhibit the proliferation, migration and the angiogenic ability of MCF7Adr cells, and can be used as an alternative drug therapy for breast cancer.

Phytotoxins: environmental micropollutants of concern?

Natural toxins such as mycotoxins or phytotoxins (bioactive compounds from fungi and plants, respectively) have been widely studied in food and feed, where they are stated to out-compete synthetic chemicals in their overall human and animal toxicological risk. A similar perception and awareness is yet largely missing for environmental safety. This article attempts to raise concern in this regard, by providing (circumstantial) evidence that phytotoxins in particular can be emitted into the environment, where they may contribute to the complex mixture of organic micropollutants. Exposures can be orders-of-magnitude higher in anthropogenically managed/affected (agro-)ecosystems than in the pristine environment.

Phytotoxic action of naphthoquinone juglone demonstrated on lettuce seedling roots

Juglone, 5-hydroxy-1,4-naphthoquinone, is the plant secondary metabolite with allelopathic properties, which was isolated especially from the plant species belonging to family Juglandaceae A. Rich. ex Kunth (walnut family). The mechanism of phytotoxic action of juglone was investigated on lettuce seedlings Lactuca sativa L. var. capitata L. cv. Merkurion by determining its effect at different levels. We have found that juglone inhibits mitosis (mitotic index 8.5 ± 0.6% for control versus 2.2 ± 0.9% for 250 μM juglone), changes mitotic phase index with accumulation of the cells in prophase (56.5 ± 2.6% for control versus 85.3 ± 5.0% for 250 μM juglone), and decreases meristematic activity in lettuce root tips (51.07 ± 3.62% for control versus 5.27 ± 2.29% for 250 μM juglone). In addition, juglone induced creation of reactive oxygen species and changed levels of reactive nitrogen species. Amount of malondialdehyde, a product of lipid peroxidation, increased from 24.0 ± 4.0 ng g(-1) FW for control to 55.5 ± 5.4 ng g(-1) FW for 250 μM juglone. We observed also changes in cellular structure, especially changes in the morphology of endoplasmic reticulum. Reactive oxygen species induced damage of plasma membrane. All these changes resulted in the disruption of the mitochondrial membrane potential, increase in free intracellular calcium ions, and DNA fragmentation and programmed cell death that was revealed by two methods, TUNEL test and DNA electrophoresis. The portion of TUNEL-positive cells increase from 0.96 ± 0.5% for control to 7.66 ± 1.5% for 250 μM juglone. Results of the study indicate complex mechanism of phytotoxic effect of juglone in lettuce root tips and may indicate mechanism of allelopathic activity of this compound.

Validation of the Antiproliferative Effects of Organic Extracts from the Green Husk of Juglans regia L. on PC-3 Human Prostate Cancer Cells by Assessment of Apoptosis-Related Genes

With the increased use of plant-based cancer chemotherapy, exploring the antiproliferative effects of phytochemicals for anticancer drug design has gained considerable attention worldwide. This study was undertaken to investigate the effect of walnut green husk extracts on cell proliferation and to determine the possible molecular mechanism of extract-induced cell death by quantifying the expression of Bcl-2, Bax, caspases-3, and Tp53. PC-3 human prostate cancer cells. In this study, we found that green husk extracts suppressed proliferation and induced apoptosis in a dose- and time-dependent manner by modulating expression of apoptosis-related genes. This involved DNA fragmentation (determined by TUNEL assay) and significant changes in levels of mRNA and the expression of corresponding proteins. An increase in expressions of Bax, caspase-3, and tp53 genes and their corresponding proteins was detected using real-time PCR and western blot analysis in PC-3 cells treated with the green husk organic extracts. In contrast, Bcl2 expression was downregulated after exposure to the extracts. Our data suggest the presence of bioactive compound(s) in walnut green husks that are capable of killing prostate carcinoma cells by inducing apoptosis and that the husks are a candidate source of anticancer drugs.

Soil degradation of parthenin-does it contradict the role of allelopathy in the invasive weed Parthenium hysterophorus L.?

The invasive success of Parthenium hysterophorus L. is thought to be partially attributable to allelopathy mediated by the plant metabolite parthenin. To assess the ecological significance of parthenin release from plant material, its persistence and phytotoxicity in soil was studied. Results show parthenin is rapidly degraded with an average DT (50) of 59 h under standard experimental conditions. Degradation was delayed in sterilized soils, at lower soil moisture, and higher parthenin concentrations. Higher temperatures, higher CEC(pot)/clay content of soils, soil preconditioning with parthenin, and P. hysterophorus infestation accelerated degradation. Physico-chemical and biological processes are, therefore, expected to govern the fate of parthenin in soil. Parthenin exhibited low soil phytotoxicity and did not accumulate over time. Along with the indicated reduction in bioavailability and development of hormetic effects, results suggest that for parthenin to have detrimental allelopathic effects, it requires high P. hysterophorus densities that result in high soil levels of parthenin and soil conditions that favor the persistence of parthenin. In light of this, the ecological significance of parthenin is discussed.

Degradation of the potato glycoalkaloid alpha-solanine in three agricultural soils

The toxic glycoalkaloids produced by the potato plant (Solanum tuberosum L.) have previously been found in upper soil from a potato field during several months. Further insight into the fate of the glycoalkaloids is needed, as only little information about their degradation in soil is available. Degradation of the glycoalkaloid, alpha-solanine, has been followed for 42d in three agricultural soils with common texture and carbon contents. A similar degradation pattern was found in all soils, and the kinetics was well described by a sum of two first-order equations. Overall, degradation rates for the initial first reaction were in the range 0.22-1.64d(-1). Estimated half-lives were in the range 1.8-4.1d for the three top soils at 15 degrees C; the fastest degradation was observed in the sandy soil. The major proportion of alpha-solanine in the sandy soil was degraded by the fast process, while the proportion was lower for the two other soils. Fast degradation appeared to be related to the presence of low amount of sorbents. Additionally, degradation was followed at 5 degrees C in A- and C-horizon soil from the sandy location, and for both horizons the half-lives were of similar length (4.7-8.7d). For the slow process, degradation rates were in the range 0.000-0.123d(-1), and residuals were still present in all soils and all temperatures at the end of the experiment (d 42). Overall, fast degradation was found in both top- and subsoil even at low temperatures, and the risk for alpha-solanine leaching to the groundwater appears to be low.

Increased age reduces DAF-16 and SKN-1 signaling and the hormetic response of Caenorhabditis elegans to the xenobiotic juglone

Cells adapt to stressors by activating mechanisms that repair damage and protect them from further injury. Stress-induced damage accumulates with age and contributes to age associated diseases. Increased age attenuates the ability to mount a stress response, but little is known about the mechanisms by which this occurs. To begin addressing this problem, we studied hormesis in the nematode Caenorhabditis elegans. When exposed to a low concentration of the xenobiotic juglone, young worms mount a robust hormetic stress response and survive a subsequent exposure to a higher concentration of juglone that is normally lethal to naïve animals. Old worms are unable to mount this adaptive response. Microarray and RNAi analyses demonstrate that an altered transcriptional response to juglone is responsible in part for the reduced adaptation of old worms. Many genes differentially regulated in young versus old animals are known or postulated to be regulated by the FOXO homologue DAF-16 and the Nrf2 homologue SKN-1. Activation of these pathways is greatly reduced in juglone stressed old worms. DAF-16- and SKN-1-like transcription factors play highly conserved roles in regulating stress resistance and longevity genes. Our studies provide a foundation for developing a molecular understanding of how age affects cytoprotective transcriptional pathways.