The present study investigated the allelopathic interference of leaf debris of Ageratum conyzoide... more The present study investigated the allelopathic interference of leaf debris of Ageratum conyzoides (billy goat weed; Asteraceae)—a weed of cultivated land—against rice (Oryza sativa). Seedling length and dry weight of rice were significantly reduced (16–20%) in soil from A. conyzoides infested fields compared to the soil from an area devoid of the weed. It indicated the presence of certain phytotoxins in the A. conyzoides infested soil. To explore the possible contribution of the weed in releasing these phytotoxins, growth studies involving leaf debris extracts and amended soils (prepared by incorporating leaf debris—5, 10, 20 g kg−1 soil, w/w, or its extracts—0.5%, 1.0% and 2.0%, v/v) were conducted. The growth of rice was severely inhibited in A. conyzoides leaf debris- and debris extract-amended soils compared to unamended control soil. A significant amount of water-soluble phenolics, the potent phytotoxins, was found in the A. conyzoides infested soil, leaf debris, and debris-amended soils. These phenolics were identified as gallic acid, coumalic acid, protocatechuic acid, catechin and p-hydroxybenzoic acid. Among these, protocatechuic acid was in the maximum amount (35.72%) followed by coumalic acid (33.49%) and these two accounted for >69% of total phenolic compounds. Further, there was a significant increase in the available nutrient content in soil amended with A. conyzoides leaf debris thus ruling out the possibility of any resource depletion upon residue incorporation and their negative role in causing growth reduction. Based on the observations, the present study concludes that leaf debris of A. conyzoides deleteriously affects the early growth of rice by releasing water-soluble phenolic acids into the soil environment and not through soil nutrient depletion.
Ageratum conyzoides L. (billy goat weed; Asteraceae) is an annual invasive weed native of tropica... more Ageratum conyzoides L. (billy goat weed; Asteraceae) is an annual invasive weed native of tropical America and has now naturalized worldwide, particularly in Southeast Asia. The present study investigated the nature and potential of root-mediated allelopathic interference of A. conyzoides against rice (Oryza sativa). Root and shoot length and biomass accumulation of rice were significantly reduced (by 18-30%) when grown in the rhizosphere soil of the weed indicating the release of putative allelochemicals from the weed into the soil. The growth of rice was also progressively reduced in the soil amended with increasing amounts of root residues (5, 10 and 20 g kg À1 soil) of A. conyzoides. The addition of activated charcoal, an inert material with high affinity for organic biomolecules, partly ameliorated the negative effects of root residues amended in the soil. Further, there was no negative effect on the availability of soil nutrients in the root-amended soils. These were rather nutrient rich with greater electrical conductivity, and higher amount of organic matter, thus indicating no role in observed growth reduction. The reduction in allelopathic effects of root residue upon charcoal addition further indicated that putative phytotoxins released from the weed roots are water-soluble phenolic compounds. A significant amount of water-soluble phenolics were present in rhizosphere ($6-times higher) and rootamended soils ($5-10-fold higher) and their content was reduced (to $3.6-7.0-fold higher) when charcoal was added. The observed growth reduction in Ageratum rhizospheric or root-amended soils was concomitant with the amount of phenolic compounds. Upon HPLC analyses, these were identified as p-coumaric acid, gallic acid, ferulic acid, p-hydroxybenzoic acid and anisic acid. Under laboratory conditions, these phenolic acids reduced the root length and seedling weight of rice individually as well as in equimolar mixture, though no synergistic effect was noticed. The study concludes that root exudates and residues of A. conyzoides suppress the growth of rice by releasing phenolic allelochemicals into the soil rhizosphere and not through alteration of soil nutrients, and allelopathy plays a significant role in root-mediated negative interference of A. conyzoides.
A study was conducted to find out the phytotoxic effect of invasive weed Ageratum conyzoides on c... more A study was conducted to find out the phytotoxic effect of invasive weed Ageratum conyzoides on chickpea (Cicer arietinum). Weed residues amended in the soil significantly reduced the chickpea growth. Root length, plant height and biomass of chickpea were lower in the soils amended with below-or above-ground weed residues. In addition, compared to control, the nodulation (nodule number, their weight and leghemoglobin content) of chickpea was also reduced in the amended soils. The observed reduction in chickpea growth and nodulation was attributed to the presence of phytotoxic phenolics in the residues. #
The present study investigated the chemical characterization, and antioxidant activity of essenti... more The present study investigated the chemical characterization, and antioxidant activity of essential oil hydrodistilled from young and mature leaves of Artemisia scoparia. GC-MS analyses revealed a monoterpenoid nature (64-67%) with 44 and 31 constituents in young and mature leaves oil, respectively. The oil from young leaf contained greater amount of oxygenated compounds. b-Myrcene (24.13%) and p-cymene (27.06%) were the major constituents in young and mature leaves oil, respectively. A. scoparia leaf oils (25-200 lg/ml) exhibited a strong 2,2-diphenyl-1-picrylhydrazyl radical scavenging capacity and antioxidant activity against hydroxyl radical and hydrogen peroxide. However, the activities of major constituent monoterpenes, b-myrcene and p-cymene, were less. In general, the DPPH radical scavenging and antioxidant activity was in the order: mature leaf oil > young leaf oil > b-myrcene > p-cymene.
The present study investigated the chemical composition and allelopathic potential of volatile oi... more The present study investigated the chemical composition and allelopathic potential of volatile oil from Eucalyptus tereticornis on growth and establishment of Amaranthus viridis, a wasteland weed. The volatile oil was rich in monoterpenoids and a total of 34 components were identified by gas chromatography/gas chromatographyÁmass spectroscopy analyses, constituting 98.52%. a-Pinene (32.5%) and 1,8-cineole (22.4%) were the two major constituents. The volatile oil and two major components were evaluated for their allelopathic potential against A. viridis. A significant reduction in early seedling growth and seedling vigor of A. viridis was observed in response to volatile oil or its major monoterpenes. Further, the contents of photosynthetic pigments, i.e. chlorophylls a and b, and carotenoids, and cellular respiration in oil-/monoterpene-treated seedlings were significantly reduced thereby indicating adverse effects of the oil on photosynthetic machinery and energy metabolism. Based on the study, it can be concluded volatile oil of E. tereticornis possess allelopathic potential and could be explored as bioherbicide for future weed management programs.
Herbs and their essential oils are known for their antimicrobial and antioxidant properties in bi... more Herbs and their essential oils are known for their antimicrobial and antioxidant properties in biological systems . Thyme (Thymus syriacus Boiss. var syriacus) and thymbra (Thymbra spicata L.) grow wild in Kurdistan-Iraq and because of their abundance in the region and use in foods their volatile oils (VO) were extracted by hydro-distillation (3) , chemically characterised (by GC and GC-MS) and evaluated for their antioxidant activities (using the Cu 2 + -mediated LDL oxidation method ). The kinetics of LDL oxidation was monitored by the change in absorbance of conjugated dienes (234 nm) over time (14 h) at 30 C. The antioxidant efficacy of the VO of each herb and their major and minor terpen(oid)s were measured by their ability to extend the lag phase of oxidation v. control .
2-Benzoxazolinone (BOA), a well-known allelochemical with strong phytotoxicity, is a potential he... more 2-Benzoxazolinone (BOA), a well-known allelochemical with strong phytotoxicity, is a potential herbicidal candidate. The aim of the present study was to determine whether phytotoxicity of BOA is due to induction of oxidative stress caused by generation of reactive oxygen species (ROS) and the changes in levels of antioxidant enzymes induced in response to BOA. Effect of BOA was studied on electrolyte leakage, lipid peroxidation (LP), hydrogen peroxide (H 2 O 2 ) generation, proline (PRO) accumulation, and activities of antioxidant enzymes-superoxide dismutase (SOD, 1.15.
We investigated the chemical composition and phytotoxicity of the essential oil extracted from le... more We investigated the chemical composition and phytotoxicity of the essential oil extracted from leaves of Artemisia scoparia Waldst. et Kit. (red stem wormwood, Asteraceae). GC/GC-MS analyses revealed 33 chemical constituents representing 99.83% of the oil. The oil, in general, was rich in monoterpenes that constitute 71.6%, with β-myrcene (29.27%) as the major constituent followed by (+)-limonene (13.3%), (Z)-β-ocimene (13.37%), and γ-terpinene (9.51%). The oil and β-myrcene were evaluated in a dose–response bioassay under laboratory conditions for phytotoxicity against three weeds—Avena fatua, Cyperus rotundus, and Phalaris minor. A significant reduction in germination, seedling growth, and dry matter accumulation was observed in the test weeds. At the lowest treatment of 0.07 mg/ml Artemisia oil, germination was reduced by 39%, 19%, and 10.6% in C. rotundus, P. minor, and A. fatua, respectively. However, the inhibitory effect of β-myrcene was less. In general, a dose-dependent effect was observed and the growth declined with increasing concentration. Among the three weeds, the inhibitory effect was greatest on C. rotundus, so it was selected for further studies. We explored the explanation for observed growth inhibition in terms of reactive oxygen species (ROS: lipid peroxidation, membrane integrity, and amounts of conjugated dienes and hydrogen peroxide)-induced oxidative stress. Exposure of C. rotundus to Artemisia oil or β-myrcene enhanced solute leakage, indicating membrane disintegration. There were increased levels of malondialdehyde and hydrogen peroxide, indicating lipid peroxidation and induction of oxidative stress. We conclude that Artemisia oil inhibits plant root growth through generation of ROS-induced oxidative damage.
Nitric oxide (NO) is a bioactive gaseous, multifunctional molecule playing a central role and med... more Nitric oxide (NO) is a bioactive gaseous, multifunctional molecule playing a central role and mediating a variety of physiological processes and responses to biotic and abiotic stresses including heavy metals. The present study investigated whether NO applied exogenously as sodium nitroprusside (SNP) has any protective role against arsenic (As) toxicity in Oryza sativa (rice). Treatment with 50 lM SNP (a NO donor) significantly ameliorated the As-induced (25 or 50 lM) decrease in root and coleoptile length of rice.
Background and Aims Determining the mode of action of allelochemicals is one of the challenging a... more Background and Aims Determining the mode of action of allelochemicals is one of the challenging aspects in allelopathic studies. Recently, allelochemicals have been proposed to cause oxidative stress in target tissue and induce an antioxidant mechanism. a-Pinene, one of the common monoterpenoids emitted from several aromatic plants including forest trees, is known for its growth-inhibitory activity. However, its mechanism of action remains unexplored. The aim of the present study was to determine the inhibitory effect of a-pinene on root growth and generation of reactive oxygen species, as indicators of oxidative stress and changes in activities of antioxidant enzymes.
2-Benzoxazolinone (BOA), a type of hydroxamic acid present in cereals and implicated in allelopat... more 2-Benzoxazolinone (BOA), a type of hydroxamic acid present in cereals and implicated in allelopathy, is now being viewed as a potential candidate for the development of natural herbicides. A study was conducted to determine the effect of BOA on mung bean (Phaseolus aureus) through a multitude of bioassays to understand its physiological and biochemical action. It was observed that BOA significantly decreased the germination of mung bean and its early growth (measured in terms of seedling length and dry weight). A typical dose–response relationship was observed with BOA treatment, and I50 values (concentrations at which 50% inhibition occurs) for germination, seedling length and seedling dry weight were calculated to be 4.3, 0.71 and 0.77 mM, respectively. There was therefore a greater inhibitory effect on seedling growth than on germination. Treated seedlings were characterised by a loss of chlorophyll and decreased respiratory activity, indicating a possible adverse effect of BOA on photosynthetic and respiratory metabolism. Mitotic activity in root-tip cells of onion (Allium cepa) was completely arrested in response to BOA treatment, and the cells exhibited abnormality in shape and size. BOA also adversely affected rhizogenesis in hypocotyl cuttings of mung bean, indicating an impact on morphogenetic potential. It was associated with significant changes in the protein content and activities of proteases and polyphenol oxidases during the root development phase. This study concludes that BOA interfered with essential biochemical processes in mung bean. Such studies provide useful information on the biochemical and physiological modes of actions of BOA, with a view to its use as a herbicidal compound.
Parthenin is a natural constituent of Parthenium hysterophorus with phytotoxic and allelopathic p... more Parthenin is a natural constituent of Parthenium hysterophorus with phytotoxic and allelopathic properties. Its effect on two weedy species viz. A6ena fatua and Bidens pilosa was studied with a view to explore its herbicidal potential. Germination of both the weeds was reduced with increasing concentration of parthenin and a dose-response relationship was observed. This provided information on LC 50 and Inhibition threshold concentrations of parthenin that could be useful for future studies. Further, parthenin also inhibited the growth of both the weeds in terms of root and shoot length and seedling dry weight. Inhibition of root growth was greater than that of shoot growth. Similar observations were made when the test weeds were grown in soil amended with different concentrations of parthenin. In addition to growth, there was a reduction of chlorophyll content in the growing seedlings. It also caused water loss in the weedy species. The study, therefore, reveals that parthenin exerts an inhibitory effect on the growth and development of both weeds and can be further explored as a herbicide for future weed management strategies.
Globally, huge amounts of synthetic herbicides are used to manage weeds in arable lands. However,... more Globally, huge amounts of synthetic herbicides are used to manage weeds in arable lands. However, their widespread use has resulted in various toxicological effects on the environment and human health, besides resulting in the emergence of herbicide-resistant weed biotypes. To overcome these problems, there is an urgent need to search for novel compounds, particularly natural plant products, with potential herbicidal activity. In this area, we studied the phytotoxic effect of volatile oil from lemon-scented eucalypt on littleseed canary grass, a noxious weed of wheat fields. Our findings show that under laboratory conditions the emergence and earlier growth of the weed decreased and completely ceased using a very low concentration of eucalypt oil (0.0714%, v/v). Treatment with eucalypt oil of the 4-week-old pot-raised weeds caused visible damage such as chlorosis and necrosis, wilting and even plant death. The effect was concentration-dependent. At low concentrations, 2.5 and 5%, v/v of eucalypt oil, plants were damaged but recovered later, whereas at concentrations higher than 5%, v/v, of eucalypt oil plants showed severe injury with little or no sign of recovery, and death. There was a severe effect on the photosynthetic and respiratory ability of treated plants 7 and 21 days after treatment. Eucalypt oil treatment caused a rapid electrolyte leakage in the P. minor leaf tissues, indicating a loss of membrane integrity. The study concludes that lemon-scented eucalypt oil offers a good option for control of littleseed canary grass and could be included as a viable component of integrated weed management under sustainable agricultural practices.
The effect of four monoterpenes - citronellol, citronellal, cineole and linalool - on the germina... more The effect of four monoterpenes - citronellol, citronellal, cineole and linalool - on the germination, growth and physiology of Cassia occidentalis was investigated. All four monoterpenes reduced germination of C. occidentalis seeds but to varying extents. Citronellal and linalool completely inhibited germination beyond the concentrations of 55 and 110 μM, respectively, whereas in response to treatment of citronellol no germination was observed beyond 330 μM. Further, the growth of seedlings, measured in terms of seedling length and biomass, was also adversely affected. A reduction in chlorophyll content of the cotyledonary leaves of C. occidentalis was also noticed, indicating an adverse effect on photosynthesis. Likewise, respiratory ability of growing seeds was also impaired in response to all four monoterpenes, clearly indicating that monoterpenes affect energy metabolism. On the basis of overall phytotoxicity, potency of monoterpenes was in the order of citronellal > linalool > citronellol > cineole. The results from this study suggest that both citronellal and linalool possess strong phytotoxic potential and can thus serve as lead molecules for the synthesis of bioherbicides.
Caffeic acid (CA) is one of the most common cinnamic acids ubiquitously present in plants and imp... more Caffeic acid (CA) is one of the most common cinnamic acids ubiquitously present in plants and implicated in a variety of interactions including allelopathy among plants and microbes. This study investigated the possible interference of CA with root growth and the process of rhizogenesis in hypocotyl cuttings of mung bean (Phaseolus aureus ¼ Vigna radiata). Results indicated that CA (0-1000 mM) significantly suppressed root growth of mung bean, and impaired adventitious root formation and root length in the mung bean hypocotyl cuttings. Further investigations into the role of CA in hampering root formation indicated its interference with the biochemical processes involved in rooting process at the three stagesroot initiation (third day; RI), root expression (fifth day; RE), and postexpression (seventh day; PE) -of rhizogenesis. CA caused significant changes in the activities of proteases, peroxidases (PODs), and polyphenol oxidases (PPOs) during root development and decreased the content of total endogenous phenolics (TP) in the hypocotyl cuttings. The enhanced activity of PODs and PPOs, though, relates to lignification and/or phenolic metabolism during rhizogenesis; yet their protective role to CA-induced stress, especially during the PE phase, is not ruled out. At 1000 mM CA, where rooting was significantly affected, TP content was very high during the RI phase, thus indicating its non-utilization. The study concludes that CA interferes ARTICLE IN PRESS www.elsevier.de/jplph 0176-1617/$ -see front matter (D.R. Batish).
Caffeic acid (CA), which is ubiquitously present in plants, is a potent phytotoxin affecting plan... more Caffeic acid (CA), which is ubiquitously present in plants, is a potent phytotoxin affecting plant growth and physiology. The aim of our study was to investigate whether CA-induced inhibition of adventitious root formation (ARF) in mung bean {Vigna radiata (L.) Wilczek [Phaseolus aureus Roxb.]} involves the induction of conventional stress responses. The effect of CA (0–1000 μM) on ARF in mung bean was determined by measuring the generation of reactive oxygen species (ROS) in terms of malondialdehyde and hydrogen peroxide (H2O2) content, root oxidizability and changes in levels of antioxidant enzymes. Our results show that CA significantly enhanced MDA content, indicating severe lipid peroxidation, and increased H2O2 accumulation and root oxidizability in the lower rooted hypocotylar region (LRHR) of mung bean, thereby inducing oxidative stress and cellular damage. In response to CA, there was a significant upregulation in the activities of scavenging enzymes, such as superoxide dismutase, ascorbate peroxidase, guaiacol peroxidase, catalase and glutathione reductase, in LRHRs of mung bean. Based on these results, we conclude that CA inhibits ARF in mung bean hypocotyls by inducing ROS-generated oxidative stress and upregulating the activities of antioxidant enzymes.
A study was conducted to assess the bioherbicidal activity of volatile oil hydrodistilled from Ar... more A study was conducted to assess the bioherbicidal activity of volatile oil hydrodistilled from Artemisia scoparia Waldst et Kit. (red stem wormwood; Asteraceae) against five weed species, viz. Achyranthes aspera, Cassia occidentalis, Parthenium hysterophorus, Echinochloa crus-galli, and Ageratum conyzoides. Emergence and seedling growth (in terms of root and shoot length) were significantly reduced in a dose-response bioassay conducted in sand impregnated with Artemisia oil (at ≥10, 25, and 50 g Artemisia oil/g sand). In general, the root length was inhibited more as compared to the shoot length and the inhibitory effect was greatest in P. hysterophorus followed by A. conyzoides and least in C. occidentalis. Post-emergence application of Artemisia oil (2%, 4%, and 6%, v/v) on 6-week-old weed plants caused visible injury (1-and 7-days after spray) ranging from chlorosis to necrosis to complete wilting of plants. Among the sprayed test weeds, the effect was greatest on E. crus-galli and P. hysterophorus. Artemisia oil treatment resulted in a loss of chlorophyll content and cellular respiration in test weeds thereby implying interference/impairment with photosynthetic and respiratory metabolism. Artemisia oil caused a severe electrolyte leakage from E. crus-galli (a monocot) and C. occidentalis (a dicot) indicating membrane disruption and loss of integrity. The study concludes that Artemisia oil has bioherbicidal properties as it causes severe phytotoxicity and interferes with the growth and physiological processes of some weed species.
The present study investigated the allelopathic interference of leaf debris of Ageratum conyzoide... more The present study investigated the allelopathic interference of leaf debris of Ageratum conyzoides (billy goat weed; Asteraceae)—a weed of cultivated land—against rice (Oryza sativa). Seedling length and dry weight of rice were significantly reduced (16–20%) in soil from A. conyzoides infested fields compared to the soil from an area devoid of the weed. It indicated the presence of certain phytotoxins in the A. conyzoides infested soil. To explore the possible contribution of the weed in releasing these phytotoxins, growth studies involving leaf debris extracts and amended soils (prepared by incorporating leaf debris—5, 10, 20 g kg−1 soil, w/w, or its extracts—0.5%, 1.0% and 2.0%, v/v) were conducted. The growth of rice was severely inhibited in A. conyzoides leaf debris- and debris extract-amended soils compared to unamended control soil. A significant amount of water-soluble phenolics, the potent phytotoxins, was found in the A. conyzoides infested soil, leaf debris, and debris-amended soils. These phenolics were identified as gallic acid, coumalic acid, protocatechuic acid, catechin and p-hydroxybenzoic acid. Among these, protocatechuic acid was in the maximum amount (35.72%) followed by coumalic acid (33.49%) and these two accounted for >69% of total phenolic compounds. Further, there was a significant increase in the available nutrient content in soil amended with A. conyzoides leaf debris thus ruling out the possibility of any resource depletion upon residue incorporation and their negative role in causing growth reduction. Based on the observations, the present study concludes that leaf debris of A. conyzoides deleteriously affects the early growth of rice by releasing water-soluble phenolic acids into the soil environment and not through soil nutrient depletion.
Ageratum conyzoides L. (billy goat weed; Asteraceae) is an annual invasive weed native of tropica... more Ageratum conyzoides L. (billy goat weed; Asteraceae) is an annual invasive weed native of tropical America and has now naturalized worldwide, particularly in Southeast Asia. The present study investigated the nature and potential of root-mediated allelopathic interference of A. conyzoides against rice (Oryza sativa). Root and shoot length and biomass accumulation of rice were significantly reduced (by 18-30%) when grown in the rhizosphere soil of the weed indicating the release of putative allelochemicals from the weed into the soil. The growth of rice was also progressively reduced in the soil amended with increasing amounts of root residues (5, 10 and 20 g kg À1 soil) of A. conyzoides. The addition of activated charcoal, an inert material with high affinity for organic biomolecules, partly ameliorated the negative effects of root residues amended in the soil. Further, there was no negative effect on the availability of soil nutrients in the root-amended soils. These were rather nutrient rich with greater electrical conductivity, and higher amount of organic matter, thus indicating no role in observed growth reduction. The reduction in allelopathic effects of root residue upon charcoal addition further indicated that putative phytotoxins released from the weed roots are water-soluble phenolic compounds. A significant amount of water-soluble phenolics were present in rhizosphere ($6-times higher) and rootamended soils ($5-10-fold higher) and their content was reduced (to $3.6-7.0-fold higher) when charcoal was added. The observed growth reduction in Ageratum rhizospheric or root-amended soils was concomitant with the amount of phenolic compounds. Upon HPLC analyses, these were identified as p-coumaric acid, gallic acid, ferulic acid, p-hydroxybenzoic acid and anisic acid. Under laboratory conditions, these phenolic acids reduced the root length and seedling weight of rice individually as well as in equimolar mixture, though no synergistic effect was noticed. The study concludes that root exudates and residues of A. conyzoides suppress the growth of rice by releasing phenolic allelochemicals into the soil rhizosphere and not through alteration of soil nutrients, and allelopathy plays a significant role in root-mediated negative interference of A. conyzoides.
A study was conducted to find out the phytotoxic effect of invasive weed Ageratum conyzoides on c... more A study was conducted to find out the phytotoxic effect of invasive weed Ageratum conyzoides on chickpea (Cicer arietinum). Weed residues amended in the soil significantly reduced the chickpea growth. Root length, plant height and biomass of chickpea were lower in the soils amended with below-or above-ground weed residues. In addition, compared to control, the nodulation (nodule number, their weight and leghemoglobin content) of chickpea was also reduced in the amended soils. The observed reduction in chickpea growth and nodulation was attributed to the presence of phytotoxic phenolics in the residues. #
The present study investigated the chemical characterization, and antioxidant activity of essenti... more The present study investigated the chemical characterization, and antioxidant activity of essential oil hydrodistilled from young and mature leaves of Artemisia scoparia. GC-MS analyses revealed a monoterpenoid nature (64-67%) with 44 and 31 constituents in young and mature leaves oil, respectively. The oil from young leaf contained greater amount of oxygenated compounds. b-Myrcene (24.13%) and p-cymene (27.06%) were the major constituents in young and mature leaves oil, respectively. A. scoparia leaf oils (25-200 lg/ml) exhibited a strong 2,2-diphenyl-1-picrylhydrazyl radical scavenging capacity and antioxidant activity against hydroxyl radical and hydrogen peroxide. However, the activities of major constituent monoterpenes, b-myrcene and p-cymene, were less. In general, the DPPH radical scavenging and antioxidant activity was in the order: mature leaf oil > young leaf oil > b-myrcene > p-cymene.
The present study investigated the chemical composition and allelopathic potential of volatile oi... more The present study investigated the chemical composition and allelopathic potential of volatile oil from Eucalyptus tereticornis on growth and establishment of Amaranthus viridis, a wasteland weed. The volatile oil was rich in monoterpenoids and a total of 34 components were identified by gas chromatography/gas chromatographyÁmass spectroscopy analyses, constituting 98.52%. a-Pinene (32.5%) and 1,8-cineole (22.4%) were the two major constituents. The volatile oil and two major components were evaluated for their allelopathic potential against A. viridis. A significant reduction in early seedling growth and seedling vigor of A. viridis was observed in response to volatile oil or its major monoterpenes. Further, the contents of photosynthetic pigments, i.e. chlorophylls a and b, and carotenoids, and cellular respiration in oil-/monoterpene-treated seedlings were significantly reduced thereby indicating adverse effects of the oil on photosynthetic machinery and energy metabolism. Based on the study, it can be concluded volatile oil of E. tereticornis possess allelopathic potential and could be explored as bioherbicide for future weed management programs.
Herbs and their essential oils are known for their antimicrobial and antioxidant properties in bi... more Herbs and their essential oils are known for their antimicrobial and antioxidant properties in biological systems . Thyme (Thymus syriacus Boiss. var syriacus) and thymbra (Thymbra spicata L.) grow wild in Kurdistan-Iraq and because of their abundance in the region and use in foods their volatile oils (VO) were extracted by hydro-distillation (3) , chemically characterised (by GC and GC-MS) and evaluated for their antioxidant activities (using the Cu 2 + -mediated LDL oxidation method ). The kinetics of LDL oxidation was monitored by the change in absorbance of conjugated dienes (234 nm) over time (14 h) at 30 C. The antioxidant efficacy of the VO of each herb and their major and minor terpen(oid)s were measured by their ability to extend the lag phase of oxidation v. control .
2-Benzoxazolinone (BOA), a well-known allelochemical with strong phytotoxicity, is a potential he... more 2-Benzoxazolinone (BOA), a well-known allelochemical with strong phytotoxicity, is a potential herbicidal candidate. The aim of the present study was to determine whether phytotoxicity of BOA is due to induction of oxidative stress caused by generation of reactive oxygen species (ROS) and the changes in levels of antioxidant enzymes induced in response to BOA. Effect of BOA was studied on electrolyte leakage, lipid peroxidation (LP), hydrogen peroxide (H 2 O 2 ) generation, proline (PRO) accumulation, and activities of antioxidant enzymes-superoxide dismutase (SOD, 1.15.
We investigated the chemical composition and phytotoxicity of the essential oil extracted from le... more We investigated the chemical composition and phytotoxicity of the essential oil extracted from leaves of Artemisia scoparia Waldst. et Kit. (red stem wormwood, Asteraceae). GC/GC-MS analyses revealed 33 chemical constituents representing 99.83% of the oil. The oil, in general, was rich in monoterpenes that constitute 71.6%, with β-myrcene (29.27%) as the major constituent followed by (+)-limonene (13.3%), (Z)-β-ocimene (13.37%), and γ-terpinene (9.51%). The oil and β-myrcene were evaluated in a dose–response bioassay under laboratory conditions for phytotoxicity against three weeds—Avena fatua, Cyperus rotundus, and Phalaris minor. A significant reduction in germination, seedling growth, and dry matter accumulation was observed in the test weeds. At the lowest treatment of 0.07 mg/ml Artemisia oil, germination was reduced by 39%, 19%, and 10.6% in C. rotundus, P. minor, and A. fatua, respectively. However, the inhibitory effect of β-myrcene was less. In general, a dose-dependent effect was observed and the growth declined with increasing concentration. Among the three weeds, the inhibitory effect was greatest on C. rotundus, so it was selected for further studies. We explored the explanation for observed growth inhibition in terms of reactive oxygen species (ROS: lipid peroxidation, membrane integrity, and amounts of conjugated dienes and hydrogen peroxide)-induced oxidative stress. Exposure of C. rotundus to Artemisia oil or β-myrcene enhanced solute leakage, indicating membrane disintegration. There were increased levels of malondialdehyde and hydrogen peroxide, indicating lipid peroxidation and induction of oxidative stress. We conclude that Artemisia oil inhibits plant root growth through generation of ROS-induced oxidative damage.
Nitric oxide (NO) is a bioactive gaseous, multifunctional molecule playing a central role and med... more Nitric oxide (NO) is a bioactive gaseous, multifunctional molecule playing a central role and mediating a variety of physiological processes and responses to biotic and abiotic stresses including heavy metals. The present study investigated whether NO applied exogenously as sodium nitroprusside (SNP) has any protective role against arsenic (As) toxicity in Oryza sativa (rice). Treatment with 50 lM SNP (a NO donor) significantly ameliorated the As-induced (25 or 50 lM) decrease in root and coleoptile length of rice.
Background and Aims Determining the mode of action of allelochemicals is one of the challenging a... more Background and Aims Determining the mode of action of allelochemicals is one of the challenging aspects in allelopathic studies. Recently, allelochemicals have been proposed to cause oxidative stress in target tissue and induce an antioxidant mechanism. a-Pinene, one of the common monoterpenoids emitted from several aromatic plants including forest trees, is known for its growth-inhibitory activity. However, its mechanism of action remains unexplored. The aim of the present study was to determine the inhibitory effect of a-pinene on root growth and generation of reactive oxygen species, as indicators of oxidative stress and changes in activities of antioxidant enzymes.
2-Benzoxazolinone (BOA), a type of hydroxamic acid present in cereals and implicated in allelopat... more 2-Benzoxazolinone (BOA), a type of hydroxamic acid present in cereals and implicated in allelopathy, is now being viewed as a potential candidate for the development of natural herbicides. A study was conducted to determine the effect of BOA on mung bean (Phaseolus aureus) through a multitude of bioassays to understand its physiological and biochemical action. It was observed that BOA significantly decreased the germination of mung bean and its early growth (measured in terms of seedling length and dry weight). A typical dose–response relationship was observed with BOA treatment, and I50 values (concentrations at which 50% inhibition occurs) for germination, seedling length and seedling dry weight were calculated to be 4.3, 0.71 and 0.77 mM, respectively. There was therefore a greater inhibitory effect on seedling growth than on germination. Treated seedlings were characterised by a loss of chlorophyll and decreased respiratory activity, indicating a possible adverse effect of BOA on photosynthetic and respiratory metabolism. Mitotic activity in root-tip cells of onion (Allium cepa) was completely arrested in response to BOA treatment, and the cells exhibited abnormality in shape and size. BOA also adversely affected rhizogenesis in hypocotyl cuttings of mung bean, indicating an impact on morphogenetic potential. It was associated with significant changes in the protein content and activities of proteases and polyphenol oxidases during the root development phase. This study concludes that BOA interfered with essential biochemical processes in mung bean. Such studies provide useful information on the biochemical and physiological modes of actions of BOA, with a view to its use as a herbicidal compound.
Parthenin is a natural constituent of Parthenium hysterophorus with phytotoxic and allelopathic p... more Parthenin is a natural constituent of Parthenium hysterophorus with phytotoxic and allelopathic properties. Its effect on two weedy species viz. A6ena fatua and Bidens pilosa was studied with a view to explore its herbicidal potential. Germination of both the weeds was reduced with increasing concentration of parthenin and a dose-response relationship was observed. This provided information on LC 50 and Inhibition threshold concentrations of parthenin that could be useful for future studies. Further, parthenin also inhibited the growth of both the weeds in terms of root and shoot length and seedling dry weight. Inhibition of root growth was greater than that of shoot growth. Similar observations were made when the test weeds were grown in soil amended with different concentrations of parthenin. In addition to growth, there was a reduction of chlorophyll content in the growing seedlings. It also caused water loss in the weedy species. The study, therefore, reveals that parthenin exerts an inhibitory effect on the growth and development of both weeds and can be further explored as a herbicide for future weed management strategies.
Globally, huge amounts of synthetic herbicides are used to manage weeds in arable lands. However,... more Globally, huge amounts of synthetic herbicides are used to manage weeds in arable lands. However, their widespread use has resulted in various toxicological effects on the environment and human health, besides resulting in the emergence of herbicide-resistant weed biotypes. To overcome these problems, there is an urgent need to search for novel compounds, particularly natural plant products, with potential herbicidal activity. In this area, we studied the phytotoxic effect of volatile oil from lemon-scented eucalypt on littleseed canary grass, a noxious weed of wheat fields. Our findings show that under laboratory conditions the emergence and earlier growth of the weed decreased and completely ceased using a very low concentration of eucalypt oil (0.0714%, v/v). Treatment with eucalypt oil of the 4-week-old pot-raised weeds caused visible damage such as chlorosis and necrosis, wilting and even plant death. The effect was concentration-dependent. At low concentrations, 2.5 and 5%, v/v of eucalypt oil, plants were damaged but recovered later, whereas at concentrations higher than 5%, v/v, of eucalypt oil plants showed severe injury with little or no sign of recovery, and death. There was a severe effect on the photosynthetic and respiratory ability of treated plants 7 and 21 days after treatment. Eucalypt oil treatment caused a rapid electrolyte leakage in the P. minor leaf tissues, indicating a loss of membrane integrity. The study concludes that lemon-scented eucalypt oil offers a good option for control of littleseed canary grass and could be included as a viable component of integrated weed management under sustainable agricultural practices.
The effect of four monoterpenes - citronellol, citronellal, cineole and linalool - on the germina... more The effect of four monoterpenes - citronellol, citronellal, cineole and linalool - on the germination, growth and physiology of Cassia occidentalis was investigated. All four monoterpenes reduced germination of C. occidentalis seeds but to varying extents. Citronellal and linalool completely inhibited germination beyond the concentrations of 55 and 110 μM, respectively, whereas in response to treatment of citronellol no germination was observed beyond 330 μM. Further, the growth of seedlings, measured in terms of seedling length and biomass, was also adversely affected. A reduction in chlorophyll content of the cotyledonary leaves of C. occidentalis was also noticed, indicating an adverse effect on photosynthesis. Likewise, respiratory ability of growing seeds was also impaired in response to all four monoterpenes, clearly indicating that monoterpenes affect energy metabolism. On the basis of overall phytotoxicity, potency of monoterpenes was in the order of citronellal > linalool > citronellol > cineole. The results from this study suggest that both citronellal and linalool possess strong phytotoxic potential and can thus serve as lead molecules for the synthesis of bioherbicides.
Caffeic acid (CA) is one of the most common cinnamic acids ubiquitously present in plants and imp... more Caffeic acid (CA) is one of the most common cinnamic acids ubiquitously present in plants and implicated in a variety of interactions including allelopathy among plants and microbes. This study investigated the possible interference of CA with root growth and the process of rhizogenesis in hypocotyl cuttings of mung bean (Phaseolus aureus ¼ Vigna radiata). Results indicated that CA (0-1000 mM) significantly suppressed root growth of mung bean, and impaired adventitious root formation and root length in the mung bean hypocotyl cuttings. Further investigations into the role of CA in hampering root formation indicated its interference with the biochemical processes involved in rooting process at the three stagesroot initiation (third day; RI), root expression (fifth day; RE), and postexpression (seventh day; PE) -of rhizogenesis. CA caused significant changes in the activities of proteases, peroxidases (PODs), and polyphenol oxidases (PPOs) during root development and decreased the content of total endogenous phenolics (TP) in the hypocotyl cuttings. The enhanced activity of PODs and PPOs, though, relates to lignification and/or phenolic metabolism during rhizogenesis; yet their protective role to CA-induced stress, especially during the PE phase, is not ruled out. At 1000 mM CA, where rooting was significantly affected, TP content was very high during the RI phase, thus indicating its non-utilization. The study concludes that CA interferes ARTICLE IN PRESS www.elsevier.de/jplph 0176-1617/$ -see front matter (D.R. Batish).
Caffeic acid (CA), which is ubiquitously present in plants, is a potent phytotoxin affecting plan... more Caffeic acid (CA), which is ubiquitously present in plants, is a potent phytotoxin affecting plant growth and physiology. The aim of our study was to investigate whether CA-induced inhibition of adventitious root formation (ARF) in mung bean {Vigna radiata (L.) Wilczek [Phaseolus aureus Roxb.]} involves the induction of conventional stress responses. The effect of CA (0–1000 μM) on ARF in mung bean was determined by measuring the generation of reactive oxygen species (ROS) in terms of malondialdehyde and hydrogen peroxide (H2O2) content, root oxidizability and changes in levels of antioxidant enzymes. Our results show that CA significantly enhanced MDA content, indicating severe lipid peroxidation, and increased H2O2 accumulation and root oxidizability in the lower rooted hypocotylar region (LRHR) of mung bean, thereby inducing oxidative stress and cellular damage. In response to CA, there was a significant upregulation in the activities of scavenging enzymes, such as superoxide dismutase, ascorbate peroxidase, guaiacol peroxidase, catalase and glutathione reductase, in LRHRs of mung bean. Based on these results, we conclude that CA inhibits ARF in mung bean hypocotyls by inducing ROS-generated oxidative stress and upregulating the activities of antioxidant enzymes.
A study was conducted to assess the bioherbicidal activity of volatile oil hydrodistilled from Ar... more A study was conducted to assess the bioherbicidal activity of volatile oil hydrodistilled from Artemisia scoparia Waldst et Kit. (red stem wormwood; Asteraceae) against five weed species, viz. Achyranthes aspera, Cassia occidentalis, Parthenium hysterophorus, Echinochloa crus-galli, and Ageratum conyzoides. Emergence and seedling growth (in terms of root and shoot length) were significantly reduced in a dose-response bioassay conducted in sand impregnated with Artemisia oil (at ≥10, 25, and 50 g Artemisia oil/g sand). In general, the root length was inhibited more as compared to the shoot length and the inhibitory effect was greatest in P. hysterophorus followed by A. conyzoides and least in C. occidentalis. Post-emergence application of Artemisia oil (2%, 4%, and 6%, v/v) on 6-week-old weed plants caused visible injury (1-and 7-days after spray) ranging from chlorosis to necrosis to complete wilting of plants. Among the sprayed test weeds, the effect was greatest on E. crus-galli and P. hysterophorus. Artemisia oil treatment resulted in a loss of chlorophyll content and cellular respiration in test weeds thereby implying interference/impairment with photosynthetic and respiratory metabolism. Artemisia oil caused a severe electrolyte leakage from E. crus-galli (a monocot) and C. occidentalis (a dicot) indicating membrane disruption and loss of integrity. The study concludes that Artemisia oil has bioherbicidal properties as it causes severe phytotoxicity and interferes with the growth and physiological processes of some weed species.
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