Autotoxic Effects Research Articles

Influence of a plasma-treated nutrient solution containing 2,4-dichlorobenzoic acid on the growth of cucumber in a hydroponic system

Allelochemicals are organic compounds exuded from the roots of plants, which have autotoxic effects on plant growth. In this study, the decomposition of 2,4-dichlorobenzoic acid (DCBA), an allelochemical of cucumber, by plasma generated in an air bubble in solution is examined, and the influence of plasma treatment of the solution on cucumber growth in a hydroponics system is investigated. Air gas is injected into water through a vertically positioned glass tube, into which a high-voltage wire electrode is placed to generate plasma. The concentration of DCBA decreases and the concentration of chloride ion produced by the dichlorination of DCBA increases with increasing discharge treatment time. Consequently, most DCBA has decomposed after 24 h of treatment. The discharge-treated solution is used as a nutrient solution for cultivating cucumber plants in a rockwool hydroponic system. The results show that the growth of most plants is inhibited by adding DCBA, as well as by the decrease in pH during discharge treatment; in contrast, plants subjected to discharge treatment with pH adjustment grow healthily.

Effects of Autotoxicity on Seed Germination, Gas Exchange Attributes and Chlorophyll Fluorescence in Melon Seedlings

In recent years, continuous cropping is more and more common in melon production, which shows significant adverse effects on melon cultivation. Autotoxicity is a critical factor for continuous cropping obstacle. The purpose of this study was to investigate whether the changes of chlorophyll fluorescence parameters could sensitively reflect the degree of melon autotoxicity and its damage. The root aqueous extract of melon plant was used to simulate the autotoxicity. The effects of autotoxicity on seed germination, seedling morphology, photosynthesis and chlorophyll a fluorescence transient (OJIP) were determined. The results showed that autotoxicity significantly inhibited seed germination and subsequent growth. The content of chlorophyll and carotenoid, photosynthetic rate, stomatal conductance, water-use efficiency and transpiration rate decreased significantly in melon seedlings under autotoxicity. The OJIP test parameters showed slight improvement or no obvious change at low treatment concentration (0.01 and 0.02 g·mL−1) and deteriorated rapidly at high concentration (0.03 and 0.04 g·mL−1), which was consistent with the concentration-dependent characteristics of autotoxicity. Under high autotoxicity stress concentration, most parameters related specific fluxes or activities per photosystem II (PS II) reaction centers (RC), such as absorption flux per active RC (ABS/RC), dissipated energy flux per active RC (DIo/RC) and other parameters, increased significantly in OJIP test. At the same time, most parameters related yields or flux ratios and performance index, such as maximum quantum yield of primary photochemistry (φPo), performance index on absorption basis (PIabs) and other parameters, decreased significantly. Photoinhibition induced by autotoxicity affected both the donor and the acceptor side of PS II, and then inhibited the growth of plants, decreased of photosynthetic pigment content. OJIP test parameters can be used to measure effectively the effect of autotoxicity on melon seedlings.

Autotoxic effects of applied vanillic acid on Dynamic succession of soil microbial community

We studied the degradation of vanillic acid in soil was studied by high performance liquid chromatography and gas chromatography. Illumina MISEQ high-throughput sequencing was used to identify the abundance of bacteria and fungi in soil. The results showed that when the concentration of vanillic acid decreased to a certain level in the soil, its degradation rate became slow. The application of vanillic acid gradually decreased the total number of bacterial OTUs in soil, while the total number of fungal OTUs increased. At the same time, the richness and diversity of bacteria were always higher than fungi. Key microbial taxa at different degradation stages of vanillic acid were identified at the phylum and genus level, including bacteria (<i>Proteobacteria, Firmicutes, Actinobacteria, Chloroflexi, Methylibium, Methylobacillus, Aeromicrobium, Pseudonocardia</i>) and Fungi (<i>Ascomycota, Zygomycota, Basidiomycota, Rhodotorula, Mortierella

Effects of Light and Autotoxicity on the Reproduction of Bidens pilosa L.: From Laboratory to the Field

In Taiwan, the good agricultural practices for Bidens pilosa L. (Cobbler’s pegs) had been established due to its pharmacology application. However, the reproduction of this species that may cause phytotoxicity to the subsequent crops has not been investigated extensively. We hypothesized that both the phytotoxicity and canopy shading conditions that were altered by agricultural practices might affect its seed reproduction. Three experiments from laboratory, pot and field were conducted under different light treatments and residue application rates to evaluate the light requirement and phytotoxicity on the germination of Cobbler’s pegs. The results showed that the germination in the laboratory, dark treatments was higher than that of light treatment while it was inhibited in the darkness in the pot experiments (24% of the light treatments). Moreover, some seeds in the pot experiments germinated in the far-red light (FR) pretreated dark treatments. This observation indicated that the germination response of the investigated plant might be a very low fluence response (VLFR). Results also showed that the autotoxicity enhanced the germination reduction in the FR pretreated dark treatment while increasing the residues buried in the field. Accordingly, both autotoxicity and canopy shading may inhibit the reproduction of Cobbler’s pegs, but the application method needs further study.

Soil scarification favors natural regeneration of Pinus pinea in Lebanon forests: Evidences from field and laboratory experiments

Pinus pinea is an important species for ecological and economic reasons in the Mediterranean area and especially in Lebanon. However, conditions of its natural regeneration have received little attention. Our study aimed to test the influence of soil disturbances, predation and autotoxicity on pine regeneration. A seed sowing field experiment was conducted in a mature stand in which two types of soil disturbances were tested (soil scarification and litter burning) in presence or absence of predation. In addition, a laboratory experiment evaluating the influence of litter (present, absent or burned) and green needle leachates (i.e. in order to mimic potential autotoxicity) on seed germination and seedling growth was conducted. Results showed a strong effect of soil disturbance, in particular soil scarification which promoted seedling emergence and early survival, whereas the role of predation was low. Forty to sixty days after seed installation, seedling density peaked at 14.9 ± 0.4 seedling.m in the scarification treatment, 13.1 ± 0.4 in the burning treatment and 8.4 ± 0.4 in the control treatment. However, an unexpected high mortality rate was recorded at the end of the field experiment in all treatments, as after seven months seedling density dropped to 0.2 ± 0.02. In the laboratory experiment, we emphasized an autotoxic effect of green needle aqueous extract on seed germination and seedling growth in the presence of litter. This allelopathic effect could be potentially linked to the presence of quinic acid which was measured as the major metabolite detected in needle aqueous extracts. In conclusion, we recommend soil preparation treatments to favor seedling emergence in combination with thinning to achieve seedling development on the long term.

Allelopathic and Autotoxic Effects of Medicago sativa-Derived Allelochemicals.

In this study, the allelopathic properties of Medicago sativa on different weeds were investigated under in vitro conditions. The compounds involved in the autotoxicity of M. sativa were analyzed using high-performance liquid chromatography. The extracts of all concentrations inhibited the growth of the calluses of Digitaria ciliaris, Chenopodium album, Amaranthus lividus, Portulaca oleracea, and Commelina communis. Six allelopathic compounds in alfalfa were identified and quantified, and the most predominant phenolic compounds were salicylic acid and p-hydroxybenzoic acid. Various concentrations (10−2, 10−3, and 10−5 M) of all the tested phenolic compounds exerted inhibitory effects on callus fresh weight. Rutin, salicylic acid, scopoletin, and quercetin significantly inhibited alfalfa seed germination. Of the seven identified saponins, medicagenic acid saponins exhibited the highest autotoxic effect and significantly lowered seed germination rate. Principal component analysis showed that the phenolic compounds and saponin composition significantly contributed to the different variables. The highly phytotoxic properties of the alfalfa-derived phenolic compounds and saponins indicate that these phytochemicals can be a potential source of bioherbicides.

Putrescine affects tomato growth and response of antioxidant defense system due to exposure to cinnamic acid

ABSTRACTThe present study deals with the mitigating effects of putrescine (Put) against cinnamic acid (CA). Cinnamic acid in root and shoot exudates of tomato (Solanum lycopersicum L.) acts as an autotoxin, inhibiting growth and metabolic activities. Put has significant role in plant growth and development, as well as in defense against abiotic and biotic challenges. There are no reports on mitigation of allelopathic effects due to CA by Put. Tomato seedlings exposed to CA decreased root and shoot length, fresh and dry weights, photosynthetic pigments, protein and sugar contents, and nitrate reductase activity. These parameters increased when Put were applied in combination with CA and alone. Lipid peroxidation enhanced in seedlings treated with CA, but decreased in combined CA-Put treatment. Histochemical staining indicated that CA-induced oxidative damage which is evident from the presence of reactive oxygen species (ROS) such as O2– and H2O2 in tomato leaves. Put decreased ROS activity and plays promising role in regulation of antioxidant enzyme activities against production of free radicals and improved seedling growth exposed to CA. Put induced tolerance of tomato seedlings to CA autotoxicity was reflected through enhanced growth of the seedlings. Our findings reveal that Put is efficient to mitigate the allelopathic and adverse effects of CA and buttressed the defense system of tomato and eliminated the autotoxic effects of endogenous CA in tomato.

Silencing of glycerol-3-phosphate acyltransferase 6 (GPAT6) gene using a newly established virus induced gene silencing (VIGS) system in cucumber alleviates autotoxicity mimicked by cinnamic acid (CA)

Autotoxicity is a serious problem for continuous cropping of cucumber, it can limit its own growth and that of nearby cucumber plants and decrease yield and quality. Cinnamic acid (CA) derivatives are a class of autotoxins that can mimic autotoxic effects in cucumber. We screened an Arabidopsis long hairpin RNA (lhRNA) library under CA-mimicked autotoxicity stress to obtain autotoxicity-resistant mutant lines. The glycerol-3-phosphate 2-O-acyltransferase 6 (GPAT6) gene was found to be silenced in one resistant mutant line, and GPAT6 homologous gene in cucumber was cloned and named CuGPAT6. To test gene function quickly, a new tobacco rattle virus (TRV)-mediated virus-induced gene silencing (VIGS) system was established in cucumber using a special agroinfiltration solution and whole cotyledonary nodes. Cucumber phytoene desaturase gene (CuPDS) and CuGPAT6 gene were successfully silenced with a newly established tobacco rattle virus (TRV)-mediated virus-induced gene silencing (VIGS) system in cucumber showing photobleaching and decreased CuPDS expression in leaves; and silencing of CuGPAT6 enhanced the tolerance to the autotoxin stress mimicked by CA in cucumber. It indicated that the alleviation of the damage caused by CA treatment was probably through maintaining the integrity of cellular structure, supporting cell vitality and promoting growth in roots, and increasing the integrate chloroplast and thylakoid numbers in leaves, which restored the growth and net photosynthesis rate of CA treated CuGPAT6 silenced plants to the similar level to those of control plants. The results also demonstrated that the newly established TRV mediated VIGS system is functional, rapid, convenient and highly efficient in cucumber.

Congeneric comparison of allelopathic and autotoxic effects of four Solidago species

The invasive species Solidago canadensis and S. gigantea are known for having the potential to inhibit their neighbours through allelopathy. However, there are no data on allelopathic properties of the natural interspecific hybrid S. ?niederederi and no investigations comparing the allelopathic potential of native and invasive Solidago species. We therefore studied the allelopathic effect of aqueous leaf extracts of S. virgaurea, S. canadensis, S. gigantea and S. ?niederederi on two congeneric pairs of species (Festuca and Solidago) occurring naturally in communities with the tested Solidago species. Germination and seedling growth of Festuca rubra were inhibited by all Solidago extracts more than were those characteristics of F. pratensis, while S. canadensis was more sensitive to its own and congeneric extracts than was S. ?niederederi. The effect of leaf type (green or withered) on Festuca seedling growth was target species-specific, while seed germination was more suppressed by green leaf extracts. The results of this study do not support the hypothesis that invasive plant species have stronger persistent allelopathic effects on native plants compared to their native congeners.

Influence of new effective allelochemicals on the distribution of Cleome arabica L. community in nature

New allelochemicals were identified through bio-guided fractionation from the ethyl acetate of seeds extracts, which was the most autotoxic compared to the other plant parts. Phytochemical investigation of the seeds extracts of C. arabica by spectroscopy analyses has led to identify two new dammarane type triterpenes (4 and 9), with nine known analogues (1 − 3, 5 − 8, 10 and 11), a new cucurbitane triterpene (12), acylated dehydrodiconiferyl alcohol (13), and three highly oxygenated flavonols (14−16). The most autotoxic compounds on germination and seedling growth were elucidated as dammarane type triterpenes. However, less autotoxic effect was recorded by an inhibition under 50% for most of the identified flavonoids. These results suggest that those autotoxic substances may be used as a new bio-herbicide that may contribute to manage the distribution of C. arabica in agronomic field.

Main Allelochemicals from the Rhizosphere Soil of Saussurea lappa (Decne.) Sch. Bip. and Their Effects on Plants' Antioxidase Systems.

Allelochemicals are the media of allelopathy and form the chemical bases of plant-environment interactions. To determine true allelochemicals and their autotoxic effects, seven compounds were isolated and identified from in-situ sampled rhizosphere soil of cultivated Saussurea lappa. Of these; costunolide (2), dehydrocostus lactone (3) and scopoletin (4) showed significant inhibition on seedling growth in a concentration-dependent manner. Detection and observation demonstrated that the antioxidase system was found to be affected by these chemicals, resulting in the accumulation of ROS and membrane damage. To investigate their release ways, the compounds were traced back and volumes quantified in rhizosphere soil and plant tissues. This work made clear the chemical bases and their physiological effects on the plants. These chemicals were found to be the secondary metabolites of the plants and included in the rhizosphere soil. The findings identified a potential pathway of plant-plant interactions, which provided theoretical basis to overcoming replanting problems. This research was also useful for exploring ecological effects of allelochemicals in green agriculture.

Assessing the Allelopathy and Autotoxicity Effects of Parthenium hysterophorus L., Senna uniflora (Mill.) H.S. Irwin and Barneby and Hyptis suaveolens (L.) Poit

In the current study laboratory experiments were conducted to elucidate the allelopathic and autotoxic effects of Parthenium hysterophorus, Senna uniflora and Hyptis suaveolens. The seed germination experiments were conducted using the leachates obtained from different organs of the three species. Ten grams, each of the plant materials were homogenized in 100 mL of quartz-distilled water for 24 hours, filtered and used as a stock solution of 100% concentration. From the stock solution, 25, 50 and 75% concentrations were prepared by diluting with quartz-distilled water. Three replicates with 30 seeds each for each plant species were maintained. Observations were made at regular intervals of 24 hours. The emergence of radicle was taken as the indicator of germination. Germination, root and shoot elongation was monitored for eight days. The study revealed inhibition of germination in both the species by the leaf leachates of P. hysterophorus of all concentrations. There was a strong and positive relationship between the concentration of the shoot and root leachates of H. suaveolens and their inhibitory effect on P. hysterophorus. The leachates of H. suaveolens, inhibited seed germination totally in P. hysterophorus in all concentrations. Allelopathic effect of leaf leachates of H. suaveolens on S. uniflora lasted longer than a week, inhibiting seed germination. The autotoxic effects of P.hysterophorus were much stronger than that of other two species. It is concluded that among the three species, H. suaveolens leaf leachates had the strongest inhibitory effect both on P. hysterophorus and S. uniflora and can be recommended as bio-herbicide.

Involvement of an autotoxic compound in asparagus decline

Asparagus (Asparagus officinalis L.) is a widely cultivated perennial veritable and can be harvested more than ten years. However, the crop quality and yield decline after a few year’s cultivation, which is called “asparagus decline”. Even though those asparagus plants were replaced with new young asparagus plants, the productivity and quality of the crop remain relatively low, which is known as a “asparagus replant problem”. One of the possible reasons for “asparagus decline” and “asparagus replant problem” is thought to be autotoxicity of asparagus. However, the compounds involved in the autotoxicity is not clear. The objective of this study was therefore to determine the potential role of autotoxicity in the “asparagus decline” and “asparagus replant problem”. An aqueous methanol extract of 10-year-asparagus-cultivated soils inhibited the growth of asparagus seedlings and other two test plants with concentration dependent manner. The result confirmed that the asparagus soils have autotoxic activity. The extract was then purified by several chromatographies with monitoring the inhibitory activity and a potent growth inhibitory substance causing the autotoxic effect was isolated. The chemical structures of the compound was determined by spectral data to be trans-cinnamic acid. trans-Cinnamic acid inhibited the growth of asparagus seedlings at concentrations greater than 10 μM. The concentrations required for 50% growth inhibition of asparagus (IC50) were 24.1–41.6 μM. trans-Cinnamic acid accumulated 174 μM in the 10-year-asparagus-cultivated soils, which may be enough levels to cause the growth inhibition on asparagus considering its IC50 value. Therefore, trans-cinnamic acid may contribute to the autotoxic effect of asparagus soils, and may be in part responsible for “asparagus decline” and “asparagus replant problem”.

Conspecific negative density dependence in a long-lived conifer, yew Taxus baccata L.

Conspecific negative density dependence in tree species can have major consequences for structuring of communities, yet in temperate forests this phenomenon remains largely unexplored. We investigated density-dependent recruitment in the long-lived conifer yew (Taxus baccata L.), for which low levels of regeneration have been linked with reduced light availability beneath conspecific canopies and speculative autotoxic effects. We combined in situ assessment of yew regeneration in a temperate forest in southwest Ireland with ex situ pot experiments to assess whether light and/or beneath conspecific canopy conditions inhibit the germination and early growth of yew. In field experiments, recruitment was related to distance from adult conspecifics, with higher levels of regeneration found in areas not beneath yew canopies. However, reduced light availability beneath the dense yew canopy was not responsible for this pattern, with abundant seedlings found in areas of equivalent or even lower light availability. Pot experiments showed that seedling survival was highest in deep shade treatments. Experiments also demonstrated that the addition of yew needles negatively affected seedling growth, but not seed germination. Together, our results suggest that under natural forest conditions, the absence of regeneration beneath mature yew canopies, often attributed to low light availability, may at least be partly related to substances in yew canopy or leaf leachates.

Phytotoxic effects of volatile and water soluble chemicals of Artemisia herba-alba

We investigated the phytotoxic effects of volatile and water soluble chemicals produced by the shrub Artemisia herba-alba Asso. We conducted a number of germination and early seedling growth bioassays on species that co-exist with A. herba-alba in natural semiarid plant communities (Salsola vermiculata L. Lygeum spartum L. Pinus halepensis Mill. and A. herba-alba itself). In addition, we assessed the phytotoxic effects of a mixture of phenols that were identified in the aqueous extract of A. herba-alba on the germination of such species. We found that volatile chemicals inhibited the germination of P. halepensis seeds, promoted the growth of P. halepensis seedlings and reduced the root biomass of S. vermiculata seedlings, while water soluble chemicals promoted the growth of L. spartum and P. halepensis seedlings. On the other hand, both volatile and water soluble compounds inhibited the germination of A. herba-alba seeds, highlighting its strong autotoxic nature. We did not find a phytotoxic effect of phenols identified (catechol, protocatechuic and vanillic acids) on species that co-exists with A. herba-alba, although they had a moderate autotoxic effect. Our results suggest that both the volatile and water soluble chemicals might be involved in chemical interactions among plants in semiarid environments.

Autotoxicity of Phthalate Esters in Tobacco Root Exudates: Effects on Seed Germination and Seedling Growth

Autotoxicity is one of the major factors that impede continuous cropping. It is defined as the toxic influence of chemicals released from one plant species on the germination and growth of individuals of the same species. Here, in order to exam the autotoxicity of tobacco root exudates, root exudates were collected from tobacco plants grown both in cultural solution and on natural soil. Using ultra-performance liquid chromatography coupled with triple-quadrupole tandem mass spectrometry, main autotoxic chemical substances in the root exudates were identified. The autotoxic effects of suspected autotoxins on seed germination (including germination rate, germination potential, germination index, and vigor index) and seedling growth were analyzed. Dibutyl phthalate (or diisobutyl phthalate), dioctyl phthalate, and diisooctyl phthalate were identified in tobacco root exudates. It was observed that high concentrations (greater than 0.5 mmol L−1) of each identified phthalate ester caused significant (P < 0.05) inhibition of tobacco seed germination and seedling growth. It can be concluded that phthalate esters such as dibutyl phthalate, diisobutyl phthalate, and diisooctyl phthalate in tobacco root exudates may play an important role in tobacco autotoxicity.

Nitrite Derived from Endogenous Bacterial Nitric Oxide Synthase Activity Promotes Aerobic Respiration.

ABSTRACTMacrophage-derived nitric oxide (NO·) is a crucial effector against invading pathogens. Yet, paradoxically, several bacterial species, including some pathogens, are known to endogenously produce NO· via nitric oxide synthase (NOS) activity, despite its apparent cytotoxicity. Here, we reveal a conserved role for bacterial NOS in activating aerobic respiration. We demonstrate that nitrite generated from endogenous NO· decomposition stimulates quinol oxidase activity in Staphylococcus aureus and increases the rate of cellular respiration. This not only supports optimal growth of this organism but also prevents a dysbalance in central metabolism. Further, we also show that activity of the SrrAB two-component system alleviates the physiological defects of the nos mutant. Our findings suggest that NOS and SrrAB constitute two distinct but functionally redundant routes for controlling staphylococcal respiration during aerobic growth.

Effects of Different Allelochemicals on the Growth and Gene Expression of Beet Seedlings

In this study, the effects of different allelochemicals on the germination of sugar beet seeds, the fresh weight and plant height of beet seedlings were studied. The allelochemicals were extracted from five kinds of plants, okra, soybean, Cichorium intybus, corn and beet. It was found that sugar beet had a serious autotoxic effect,and the allelopathic material of Cichorium intybus also inhibited the growth of sugar beet seedlings, while the other allelopathic substances promoted the growth of the seedlings. It is found that all the allelochemicals can effectively promote the production of pigments in beet seedling, but the treatment effects of the allelochemicals are different. What is more, the expression of UDP-GT and TYR gene was measured,and the relationship between pigment content and gene expression was found to be closely related, but the specific impact pathway still need to be further studied.

Physiological effects of autotoxicity due to DHAP stress on Picea schrenkiana regeneration

Picea Schrenkiana as one of the most important zonal vegetation was an endemic species in Middle Asia. Natural regeneration of P. Schrenkiana is a long existing problem troubling scientists. The autotoxicity of 3,4-dihydroxy-acetophenone (DHAP) was found to be a causative factor causing the failure of P. Schrenkiana natural regeneration. The effects of concentrations of DHAP treatment on the viability of root cell, activities of antioxidant enzymes and levels of P. Schrenkiana phytohormones were performed to disclose the physiological mechanism of DHAP autotoxicity. It was observed that high concentration of DHAP could inhibit the seed germination and seedling growth, but had a hormesis at low concentrations. Analyses showed that the root cells significantly lost their viability treated with high DHAP. The enzymes activities of seedlings were significantly stimulated by the treatment of 0.5 mM DHAP to give a transient increase and then decrease as DHAP concentration increased to 1.0 mM except for GR (glutathione reductase) in which DHAP treatment had little effect on its activity. Comparing with the control, an increase in the levels of phytohormones ZT (zeatin), GA3 (gibberellic acid) and IAA (indole acetic acid) was induced by the treatment of DHAP at low concentrations (0.1–0.25 mM), but the significant deficiency was found treated by high concentrations (0.5–1.0 mM). In addition, the ABA (abscisic acid) level increased in all experimental observations. These results suggested that DHAP significantly affected indices of growth and physiology, and provided some new information about different effect in P. Schrenkiana treated with DHAP.

Codonopilate A, a Triterpenyl Ester as Main Autotoxin in Cultivated Soil of Codonopsis pilosula (Franch.) Nannf.

Codonopilate A (1), a triterpenyl ester, was isolated from monocultivated soil of annual Codonopsis pilosula and identified as the main autotoxin. The yield ratio of codonopilate A in dried soil was calculated as 2.04 μg/g. Other two triterpenoids, taraxeryl acetate (2) and 24-methylenecycloartanol (3), were isolated and identified as well showing weaker autotoxity. This was the first time that the potential allelochemicals and autotoxins in the cultivated soil of Codonopsis pilosula were reported. Accumulation of reactive oxygen species (ROS) induced by the autotoxins in the root tips of Codonopsis pilosula was considered as an important factor for the phytotoxic effect. This work systematically investigates the allelopathic and autotoxic effect of Codonopsis pilosula, and the preliminary autotoxic action mode of the three autotoxins. These findings are helpful to understand the molecular mechanism of autotoxicity and conducive to explore proper ways to degrade the autotoxins and eliminate the replanting problems of Codonopsis pilosula.