Ecology, Biology, Environmental Impacts, and Management of an Agro-Environmental Weed Ageratum conyzoides

Ageratum conyzoides L. (Billy goat weed; Asteraceae) is an annual herbaceous plant of American origin with a pantropical distribution. The plant has unique biological attributes and a raft of miscellaneous chemical compounds that render it a pharmacologically important herb. Despite its high medicinal value, the constant spread of the weed is noticeable and alarming. In many countries, the weed has severely invaded the natural, urban, and agroecosystems, thus presenting management challenges to natural resource professionals and farmers. Its interference with agricultural crops, grassland forbs, forest ground flora, and its ability to replace native plant species are of serious concern. Therefore, it is pertinent to monitor its continuous spread, its entry into new geographic regions, the extent of its impact, and the associated evolutionary changes. While management strategies should be improvised to control its spread and reduce its adverse impacts, the possible utilization of this noxious weed for pharmacological and agronomic purposes should also be explored. The objective of this review is to provide a detailed account of the global distribution, biological activities, ecological and environmental impacts, and strategies for the management of the agro-environmental weed A. conyzoides.

Seed size dimorphism in Hyptis suaveolens aids in differentiation of the germination niche

Seed germination characteristics help predict the degree of invasive success of a species based on capacity of the seeds to germinate and recruit into novel habitats. Hyptis suaveolens (L.) Poit. (Bush mint, Pignut; Lamiaceae) is an invasive plant that is spreading throughout tropical and subtropical regions worldwide. We conducted a study to understand the role of seed size dimorphism in differentiation of germination niche in H. suaveolens. We subjected small and large seeds to varying environmental conditions of temperature (°C), photoperiod (light/dark), salt (NaCl; mM), pH, osmotic potential (MPa), different soil types and ratios (clay:sand) and burial depth (cm). Different germination indices were calculated and their interaction with seed dimorphism studied. There was a significant interaction (P < 0.001) between germination indices and seed dimorphism throughout the treatments. Large seeds had higher germination percentage and rate, indicating higher germination capacity. In addition, these displayed more asynchronous germination under various environments. Small seeds, on the other hand, required a longer germination time as compared to large seeds, indicating slower germination. Differential responses of the two seed morphs to varying environmental conditions, therefore, help H. suaveolens to differentiate its germination niche and establish in heterogeneous environments. These findings will help in devising appropriate management and eradication strategies based on germination ecology of seeds.

β-Pinene alleviates arsenic (As)-induced oxidative stress by modulating enzymatic antioxidant activities in roots of Oryza sativa

Rice (Oryza sativa L.) is a highly consumed staple crop worldwide, but abiotic/heavy metal stresses acting on the plant cause reduction in yield and quality, thereby impacting global food security. In the present study, we examined the effect of β-pinene against Arsenic (As)-induced oxidative damage vis-à-vis regulation of activities of enzymatic antioxidants in roots of O. sativa. Effect of As (50 μM), β-pinene (10 μM; β-10) and As + β-10 treatments on root length, shoot length, As accumulation, lipid peroxidation (as malondialdehyde [MDA] content), hydrogen peroxide (H₂O₂) accumulation, and activities of lipoxygenase (LOX) and enzymatic antioxidants such as ascorbate peroxidase (APX), guaiacol peroxidase (GPX), glutathione reductase (GR), superoxide dismutase (SOD), and catalase (CAT) was determined. Exposure of As caused a decline in root and shoot length, and enhancement in As accumulation, lipid peroxidation, and activities of enzymatic antioxidants. However, supplementation of β-10 (i.e., As + β-10 treatments) led to an increase in root and shoot length. Treatment with As + β-10 resulted in a decline in As accumulation, H₂O₂ content, and MDA content; however, the effect on LOX activity was non-significant, as compared to control. Similarly, with As + β-10 treatment a reduction in the activities of APX, GPX, GR, SOD, and CAT was observed as compared with As-alone treatment. Pearson's correlation matrix exhibited strong negative correlation between reactive oxygen species (ROS) and root/shoot length, whereas a strong positive correlation was observed between antioxidant enzymes and ROS. The present study demonstrated that β-pinene significantly ameliorates As-induced oxidative stress and provides tolerance to O. sativa against As-induced toxicity, and thus offer an option of As-mitigation using environment friendly natural plant products. However, to gain insights into the function of β-pinene in modulating As-induced oxidative damage in plants, further field investigations and exploration of its mechanism of action are needed.

Essential oils as anticancer agents: Potential role in malignancies, drug delivery mechanisms, and immune system enhancement

Cancer retains a central place in fatality rates among the wide variety of diseases known world over, and the conventional synthetic medicaments, albeit used until now, produce numerous side effects. As a result, newer, better, and safer alternatives such as natural plant products, are gravely required. Essential oils (EOs) offer a plethora of bioactivities including antibacterial, antiviral, antioxidant, and anticancer properties, therefore, the use of EOs in combination with synthetic drugs or aromatherapy continues to be popular in many settings. In view of the paramount importance of EOs and their potential bioactivities, this review summarizes the current knowledge on the interconnection between EOs and cancer treatment. In particular, the current review presents an updated summary of the chemical composition of EOs, their current applications in cancer treatments based on clinical studies, and the mechanism of action against the cancer cell lines. Similarly, an overview of using EOs in aromatherapy and enhancing immunity during cancer treatment is provided. Further, this review focuses on the recent technological advancements such as the loading of EOs using protein microspheres, ligands, or nanoemulsions/nanoencapsulation, which offer multiple benefits in cancer treatment via site-specific and target-oriented delivery of drugs. The continuing clinical studies of EOs implicate that their pharmacological applications are a rewarding research area.

Amelioration potential of β-pinene on Cr(VI)-induced toxicity on morphology, physiology and ultrastructure of maize

Heavy metals' amassment in the soil environment is a threat to crop and agricultural sustainability and consequentially the global food security. For achieving enhancement of crop productivity in parallel to reducing chromium (Cr) load onto food chain demands continuous investigation and efforts to develop cost-effective strategies for maximizing crop yield and quality. In this context, we investigated the amelioration of Cr(VI) toxicity through β-pinene in experimental dome simulating natural field conditions. The protective role of β-pinene was determined on physiology, morphology and ultrastructure in Zea mays under Cr(VI) stress (250 and 500 μM). Results exhibited a marked reduction in the overall growth (shoot and root length and dry matter) of Z. mays plants subjected to Cr(VI) stress. Photosynthetic pigments (chlorophyll and carotenoids) were evidently reduced, and there was a loss of membrane integrity. Supplementation of β-pinene (100 μM), however, declined the toxicity induced by Cr(VI). Interestingly, Cr-tolerant abilities were improved in relation to plant growth, photosynthetic pigments and membrane integrity with the combined treatment of Cr(VI) and β-pinene. β-Pinene also reduced the root-mediated uptake of Cr(VI) and translocation to shoots. Moreover, significant ultrastructural damages recorded in roots and shoots under Cr(VI) stress were partially reverted upon addition of β-pinene. Our analyses revealed that β-pinene mitigates Cr(VI) toxicity in Z. mays, either by membrane stabilization or serving as a barrier to the uptake of Cr from soil. Thus, exogenous supply of β-pinene can be an effective alternative to mitigate Cr toxicity in soil. However, it is deemed essential to investigate further the responses throughout the life cycle of the plant on β-pinene supplementation under natural conditions.

Salicylic acid pre-treatment modulates Pb2+-induced DNA damage vis-à-vis oxidative stress in Allium cepa roots

The current study investigated the putative role of salicylic acid (SA) in modulating Pb²⁺-induced DNA and oxidative damage in Allium cepa roots. Pb²⁺ exposure enhanced free radical generation and reduced DNA integrity and antioxidant machinery after 24 h; however, SA pre-treatment (for 24 h) ameliorated Pb²⁺ toxicity. Pb²⁺ exposure led to an increase in malondialdehyde (MDA) and hydrogen peroxide (H₂O₂) accumulation and enhanced superoxide radical and hydroxyl radical levels. SA improved the efficiency of enzymatic antioxidants (ascorbate and guaiacol peroxidases [APX, GPX], superoxide dismutases [SOD], and catalases [CAT]) at 50-μM Pb²⁺ concentration. However, SA pre-treatment could not improve the efficiency of CAT and APX at 500 μM of Pb²⁺ treatment. Elevated levels of ascorbate and glutathione were observed in A. cepa roots pre-treated with SA and exposed to 50 μM Pb²⁺ treatment, except for oxidized glutathione. Nuclear membrane integrity test demonstrated the ameliorating effect of SA by reducing the number of dark blue-stained nuclei as compared to Pb²⁺ alone treatments. SA was successful in reducing DNA damage in cell exposed to higher concentration of Pb²⁺ (500 μM) as observed through comet assay. The study concludes that SA played a major role in enhancing defense mechanism and protecting against DNA damage by acclimatizing the plant to Pb²⁺-induced toxicity.

Cytotoxic and genotoxic assessment of agricultural soils from an industrial region

Industrial effluents contain hazardous substances that can be a serious threat to the agriculture and human health. In the present study, the cytotoxic and genotoxic impacts of agricultural soil from the industrial area of Dera Bassi (Punjab, India) have been evaluated. Assays such as defects in DNA repair in K-12 mutants of Escherichia coli and chromosomal aberrations in Allium cepa were used to estimate the acute toxicity and chromosomal mutagenesis, respectively. Atomic absorption spectrometry and GC-MS analysis revealed contamination of the soil with high concentrations of heavy metals and organic compounds, respectively. Dichloromethane extract of site I soil sample caused maximum damage to 40 μL mL^-1 DNA repair defective mutants and showed 38 and 49% survival in lexA and recA mutants, respectively, which was least among all the sites. In A. cepa test, an inverse relationship between soil extract concentration and the mitotic index was observed. Exposure of growing roots of A. cepa to soil extracts induced chromosomal abnormalities and alterations in mitotic phases in root tip cells. The study concludes that agricultural sites near the industrial area were contaminated with genotoxic and mutagenic compounds. Hence, adequate measures should be taken to reduce the toxicity of industrial effluents discharged onto the agricultural fields.

Nature of phytotoxic interference of alien weed 'Calyptocarpus vialis' against some crop plants

Calyptocarpus vialis (syn. Synedrella vialis; Asteraceae), a native of the tropical Americas, has acquired an invasive status in the eastern Asia and Africa and, of late, in India. It is an annual herbaceous weed that forms a dominant ground cover due to its prostrate expansion and interferes with the growth of other plant species. However, the reasons for this interference are largely unknown. Therefore, we examined the allelopathic interference of C. vialis via leachation and residue degradation on the emergence, growth, and development of three crop species (Brassica nigra, Triticum aestivum, and Avena sativa). In a laboratory bioassay, the leachates (0.5-4%) of C. vialis exhibited a dose-dependent inhibitory effect on various growth parameters of the test plants. Similarly, under screenhouse, C. vialis-amended soil (1-4%) affected the growth of test species in a dose-dependent manner. Further, the phytotoxicity of the residues of C. vialis was examined using rhizospheric soil (RS) and residue-amended soil (RAS). It was observed that RAS exerted the maximum allelopathic effect on the test species accompanied by significant changes in pH, electrical conductivity, and total water-soluble phenolic content, as compared with the control soil (CS) and RS. Liquid chromatography and mass spectroscopy analyses confirmed the presence of eleven allelochemicals as the major phytotoxins. The study demonstrated that C. vialis exerts strong phytotoxic effects on other plants through the release of potent allelochemicals, both via leachation and residue degradation.

Documentation and validation of climate change perception of an ethnic community of the western Himalaya

The high-altitude regions of Himalaya are among the best indicators of climate change yet noticeable for the lack of climate monitoring stations. However, they support ethnic communities whose livelihood activities are climate driven. Consequently, these communities are keen observers of the same and documenting their perception on changing climate is now an important area of global research. Therefore, the present study was conducted with the prime objective of documenting the climate change perception of Bhangalis-a resident community of western Himalaya, and analyzing variation in their perceptions in relation to age and gender. For this, respondent surveys (household, n = 430; individual interviews, n = 240) were carried out and the collected data were subjected to statistical analyses. The study also validated the perception of Bhangalis using the available weather data (1974-2017) through the Mann-Kendall test. The results reveal that Bhangalis perceived 11 indicators of changing climate, of which decrease in snowfall was the most prominent (reported by ~ 97% of the respondents). The perceptions varied between the two genders with males having significantly higher proportion of responses for all the 11 indicators. Similarly, differences in perception among the age groups were also observed, elderly people reported higher proportion of climate change indicators as compared to respondents of lower age. Notably, patterns of temperature and rainfall perceptions by the Bhangalis agreed with the trends of meteorological data. This highlights the importance of the study in documenting knowledge of ethnic communities especially from areas that lack monitoring stations. It argues for involving them in climate change programs.

Chemical characterization, phytotoxic, and cytotoxic activities of essential oil of Mentha longifolia

The present study assessed the phytotoxic and cytotoxic potential of the essential oil (EO) extracted from aboveground parts of Mentha longifolia (L.) Huds. Gas chromatography-mass spectrometry revealed 39 compounds constituting 99.67% of the EO. The EO was rich in monoterpenoids (mostly oxygenated monoterpenes), which accounted for 89.28% of the oil. The major components in EO were monoterpene ketones such as piperitone oxide (53.83%) and piperitenone oxide (11.52%), followed by thymol (5.80%), and (E)-caryophyllene (4.88%). The phytotoxic activities of EO were estimated against Cyperus rotundus, Echinochloa crus-galli, and Oryza sativa (rice) through pre- and post-emergence assays at concentrations ranging from 10 to 250 μg/ml and 0.5-5%, respectively. In pre-emergence assay, the phytotoxic effect of EO was most pronounced on C. rotundus, thereby significantly affecting percent germination, plantlet growth, and chlorophyll content. On the contrary, the impact was comparatively lesser on rice, with ~ 40% germination in response to 250 μg/ml of EO treatment. In the post-emergence assay, the spray treatment of EO caused a loss of chlorophyll and wilting in test plants, and subsequently affected the growth of plants, even leading to death in some cases. The cytotoxic activity of EO (at 2.5-50 μg/ml) was studied in meristem cells in onion (Allium cepa L.) root tips. EO exposure to the onion roots induced various chromosomal aberrations such as chromosomal bridges, c-mitosis, stickiness, vagrant chromosomes, etc., and negatively affected the mitotic index. At 50 μg/ml, EO treatment triggered the complete death of roots. The study concludes that M. longifolia EO has phytotoxic activities due to the mito-depressive effect, along with other physiological effects on target plants. Therefore, EO of M. longifolia could be developed into a novel bioherbicide for sustainable management of weeds in agricultural systems.

Comparative cyto- and genotoxicity of 900 MHz and 1800 MHz electromagnetic field radiations in root meristems of Allium cepa

In the last few decades, tremendous increase in the use of wireless electronic gadgets, particularly the cell phones, has significantly enhanced the levels of electromagnetic field radiations (EMF-r) in the environment. Therefore, it is pertinent to study the effect of these radiations on biological systems including plants. We investigated comparative cytotoxic and DNA damaging effects of 900 and 1800 MHz EMF-r in Allium cepa (onion) root meristematic cells in terms of mitotic index (MI), chromosomal aberrations (CAs) and single cell gel electrophoresis (comet assay). Onion bulbs were subjected to 900 and 1800 MHz (at power densities 261 ± 8.50 mW m^-2 and 332 ± 10.36 mW m^-2, respectively) of EMF-r for 0.5 h, 1 h, 2 h, and 4 h. Root length declined by 13.2% and 12.3%, whereas root thickness was increased by 46.7% and 48.3% after 4 h exposure to 900 MHz and 1800 MHz, respectively. Cytogenetic studies exhibited clastogenic effect of EMF-r as depicted by increased CAs and MI. MI increased by 36% and 53% after 2 and 4 h exposure to 900 MHz EMF-r, whereas it increased by 41% and 67% in response to 1800 MHz EMF-r. Aberration index was increased by 41%-266% and 14%-257% during 0.5-4 h of exposure to 900 MHz and 1800 MHz, respectively, over the control. EMF-r exposure decreased % head DNA (DNAH) and increased % tail DNA (DNAT) and olive tail moment (OTM) at both 900 and 1800 EMF-r. In 4 h exposure treatments, head DNA (%) declined by 19% and 23% at 900 MHz and 1800 MHz, respectively. DNAT and OTM were increased by 2.3 and 3.7 fold upon exposure to 900 MHz EMF-r over that in the control, whereas 2.8 and 5.8 fold increase was observed in response to 1800 MHz EMF-r exposure for 4 h and the difference was statistically significant. The study concludes that EMF-r in the communication range (900 and 1800 MHz) adversely affect root meristems in plants and induce cytotoxic and DNA damage. EMF-r induced DNA damage was more pronounced at 1800 MHz than that at 900 MHz.

Appraisal of immediate and late effects of mobile phone radiations at 2100 MHz on mitotic activity and DNA integrity in root meristems of Allium cepa

The present study evaluated the potential of 2100 MHz radiofrequency radiations to act as cytotoxic and genotoxic agent. Fresh onion (Allium cepa L.) roots were exposed to electromagnetic field radiations (EMF-r) for different durations (1 h and 4 h) and evaluated for mitotic index (MI), phase index, chromosomal aberrations, and DNA damage. DNA damage was investigated with the help of the comet assay by assessing various parameters like % head DNA (HDNA), % tail DNA (TDNA), tail moment (TM), and olive tail moment (OTM). Effects of EMF-r exposure were also compared with that of methyl methanesulfonate (MMS; 90 μM), which acted as a positive control. The post-exposure effects of EMF-r after providing the test plants with an acclimatization period of 24 h were also evaluated. Compared to the control, a significant increase in the MI and aberration percentage was recorded upon 4 h of exposure. However, no specific trend of phase index in response to exposure was detected. EMF-r exposure incited DNA damage with a significant decrease in HDNA accompanied by an increase in TDNA upon exposure of 4 h. However, TM and OTM did not change significantly upon exposure as compared to that of control. Analysis of the post-exposure effects of EMF-r did not show any significant change/recovery. Our data, thus, suggest the potential cytotoxic and genotoxic nature of 2100 MHz EMF-r. Our study bears great significance in view of the swiftly emergent EMF-r in the surrounding environment and their potential for inciting aberrations at the chromosomal level, thus posing a genetic hazard.

24-Epibrassinolide pre-treatment reduces alkaline-induced oxidative stress in red rice seedlings

Soil alkalinity caused by salts, such as sodium bicarbonate (NaHCO₃), and the frequently associated waterlogging problems are pervasive in agriculture and have a deleterious impact on crop production. However, various plant growth regulators, including brassinosteroids, are considered to be important against different abiotic stresses experienced by plants due to drought, salinity, and heavy metal stress. We investigated the putative role of 24-epibrassinolide (EBL), an active brassinosteroid, on red rice plants experiencing alkaline stress. Seedlings were pre-treated with 0.01 μM EBL for 30 min and later, exposed to NaHCO₃ (25 mM) and were sampled, 5 days after treatments. Results showed that the pre-treatment of seedlings with EBL under non-stress conditions could promote rice plant growth. Growth parameters including dry weight (DW), root and coleoptile lengths were reduced under alkaline stress, whereas EBL application reduced the level of inhibition, as compared with NaHCO₃ treatment. Enhanced levels of malondialdehyde content, hydrogen peroxide, and superoxide radicals were significantly diminished by EBL pre-treatment. Moreover, pre-treatment of EBL to alkaline-treated rice seedlings largely stimulated the enzymatic activities of ascorbate peroxidase, catalase, and superoxide dismutase. Thus, the results suggest that pre-application of EBL significantly ameliorates alkaline stress in rice.

Nitric oxide induced modulations in adventitious root growth, lignin content and lignin synthesizing enzymes in the hypocotyls of Vigna radiata

The present study evaluated the role of nitric oxide (NO) in mediating adventitious root (AR) growth, lignification and related enzymatic changes in the hypocotyls of Vigna radiata. To meet the objectives, the changes in AR growth, lignin content, and the activities of enzymes-peroxidases, polyphenol oxidases, and phenylalanine ammonia lyases- with NO donor and its scavenger were monitored. Hypocotyls were cultivated in aqueous solution supplemented with different concentrations of SNP (sodium nitroprusside, NO donor compound) and its scavenging compound (2,4-carboxyphenyl-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide; cPTIO). Specifically, at low concentrations, SNP induced AR growth, increased the total lignin content and altered the activities of related oxidoreductases- peroxidases, polyphenol oxidases and phenylalanine ammonia lyases- which are involved in lignin biosynthesis pathway. At higher concentrations, a decline in AR growth and lignification was noticed. We analysed the function of NO in AR formation by depleting the endogenous NO using scavenging compound cPTIO. Hypocotyls grown in a medium supplemented with scavenger cPTIO exhibited significant decline in AR growth and the activities of lignin synthesizing enzymes. Application of NO scavenger showed that stimulatory properties on root lignification may be owing to NO itself. In addition, changes in AR growth were significantly correlated with these modified biochemical activities. Our analysis revealed that NO supplementation induces prominent alterations in lignin level during AR formation and this might be due to an alteration in the activity of lignin biosynthetic enzymes, which further affected the polymerization of monolignols and AR growth.

Phenotypic variations alter the ecological impact of invasive alien species: Lessons from Parthenium hysterophorus

Invasive plant species constantly adjust their behavior with ecological shifts by virtue of phenotypic plasticity and/or local adaptations. Changes in the phenotype of an invasive species may also trigger variations in its community level impacts, which is an acceptable, yet unexplored aspect of invasion biology. Our study attempts to fill important knowledge gaps on the basic behavior and ecological interactions of invasive species. Parthenium hysterophorus, a widely distributed invasive alien species of tropical and sub-tropical regions, was evaluated for variations in its morpho-functional traits and ecological performance at a common spatial and temporal scale. Field surveys were conducted in Chandigarh, India, in five sites identified as invaded with P. hysterophorus. Individuals of P. hysterophorus randomly sampled from these sites, showed from trait analyses that the population is differentiated into two morphotypes, P_A and P_B. Morphotype P_B exhibits traits comparable to the shrub life-form in terms of woody stem (with higher stem circumference [+32.26%], stem specific density [+128.57%], twig dry matter content [+25.15%]); profuse branching (+46.38%); larger canopy (+91.16%); and better reproductive output (+190.29%) compared to P_A. P_A, on the other hand, reflected herbaceous characteristics with greater leaf area (+67.58%) and higher content of chlorophyll (+21.92%) compared to P_B. Based on these morphotypes, the plots were divided into three invasion categories: areas invaded by P_A [IP_A], areas invaded by P_B [IP_B] and uninvaded areas [UI]. Ecological indices and soil chemical properties were compared across IP_A, IP_B and UI. Shannon's index (p < 0.001), evenness index (p = 0.008), and richness index (p < 0.001) were significantly lower in IP_B compared to IP_A. UI areas were found to have higher soil pH, phenolics, organic matter, and concentrations of N, P and K, compared to IP_A and IP_B, but lower Ca and Mg. Results suggest that phenotypic variations within population of P. hysterophorus regulate its ecological impact on associated vegetation. Conservation managers would benefit from studying its invasion patterns and identifying the morphotype with higher ecological impact to prioritize management efforts. Monitoring these behavioral and ecological patterns in P. hysterophorus over the long-term may also help in anticipating challenges to preventive measures.

Exposure to mobile phone radiations at 2350 MHz incites cyto- and genotoxic effects in root meristems of Allium cepa

BACKGROUND

The exponential increase of electromagnetic field radiations (EMF-r) in the natural environment has raked up the controversies regarding their biological effects. Concern regarding the putative capacity of EMF-r to affect living beings has been growing due to the ongoing elevation in the use of high frequency EMF-r in communication systems, e.g. Mobile phones.

METHODS

In the present study, we tried to examine the cyto- and genotoxic potential of mobile phone EMF-r at 2350 MHz using onions (Allium cepa L.). Fresh adventitious onion roots were exposed to continuous EMF-r at 2350 MHz for different time periods (1 h, 2 h and 4 h). The evaluation of cytotoxicity was done in terms of mitotic index (MI), phase index and chromosomal aberrations. Genotoxicity was investigated employing comet assay in terms of changes in % HDNA (head DNA) and % TDNA (tail DNA), TM (tail moment) and OTM (olive tail moment). Data were analyzed using one-way ANOVA and mean values were separated using post hoc Tukey's test.

RESULTS

The results manifested a significant increase of MI and chromosomal aberrations (%) upon 4 h, and ≥ 2 h of exposure, respectively, as compared to the control. No specific changes in phase index in response to EMF-r exposure were observed. The % HDNA and % TDNA values exhibited significant changes in contrast to that of control upon 2 h and 4 h of exposure, respectively. However, TM and OTM did not change significantly.

CONCLUSIONS

Our results infer that continuous exposures of radiofrequency EMF-r (2350 MHz) for long durations have a potential of inciting cyto- and genotoxic effects in onion root meristems.

Biochemical Adaptations in Zea mays Roots to Short-Term Pb(2+) Exposure: ROS Generation and Metabolism

The present study investigated the effect of lead (0, 16, 40 and 80 mg L(-1) Pb2+) exposure for 3, 12 and 24 h on root biochemistry in hydroponically grown Zea mays (maize). Pb2+ exposure (80 mg L(-1)) enhanced malondialdehyde content (239%-427%), reactive carbonyl groups (425%-512%) and H2O2 (129%-294%) accumulation during 3-24 h of treatment, thereby indicating cellular peroxidation and oxidative damage. The quantitative estimations were in accordance with in situ detection of ROS generation (using 2',7'-dichlorodihydrofluorescein diacetate dye) and H2O2 accumulation. Pb2+ treatment significantly reduced ascorbate and glutathione content during 3-24 h of exposure. On the contrary, levels of non-protein thiols were enhanced by 3-11.8 time over control in response to 16-80 mg L(-1) Pb2+ treatment, after 24 h. A dose-dependent induction in ascorbate peroxidase and lipoxygenase enzyme activity was observed in Z. mays roots. The activities of ascorbate-recycling enzymes (dehydroascorbate reductase and monodehydroascorbate reductase) were significantly increased in relation to concentration and duration of Pb2+ treatment. The study concludes that Pb2+-exposure induces ROS-mediated oxidative damage during early period of exposure despite the upregulation of enzymes of ascorbate-glutathione cycle.

Eugenol-inhibited root growth in Avena fatua involves ROS-mediated oxidative damage

Plant essential oils and their constituent monoterpenes are widely known plant growth retardants but their mechanism of action is not well understood. We explored the mechanism of phytotoxicity of eugenol, a monoterpenoid alcohol, proposed as a natural herbicide. Eugenol (100-1000 µM) retarded the germination of Avena fatua and strongly inhibited its root growth compared to the coleoptile growth. We further investigated the underlying physiological and biochemical alterations leading to the root growth inhibition. Eugenol induced the generation of reactive oxygen species (ROS) leading to oxidative stress and membrane damage in the root tissue. ROS generation measured in terms of hydrogen peroxide, superoxide anion and hydroxyl radical content increased significantly in the range of 24 to 144, 21 to 91, 46 to 173% over the control at 100 to 1000 µM eugenol, respectively. The disruption in membrane integrity was indicated by 25 to 125% increase in malondialdehyde (lipid peroxidation byproduct), and decreased conjugated diene content (~10 to 41%). The electrolyte leakage suggesting membrane damage increased both under light as well as dark conditions measured over a period from 0 to 30 h. In defense to the oxidative damage due to eugenol, a significant upregulation in the ROS-scavenging antioxidant enzyme machinery was observed. The activities of superoxide dismutases, catalases, ascorbate peroxidases, guaiacol peroxidases and glutathione reductases were elevated by ~1.5 to 2.8, 2 to 4.3, 1.9 to 5.0, 1.4 to 3.9, 2.5 to 5.5 times, respectively, in response to 100 to 1000 µM eugenol. The study concludes that eugenol inhibits early root growth through ROS-mediated oxidative damage, despite an activation of the antioxidant enzyme machinery.

Morphological, anatomical, and ultrastructural changes (visualized through scanning electron microscopy) induced in Triticum aestivum by Pb²⁺ treatment

Lead (Pb) causes severe damage to crops, ecosystems, and humans, and alters the physiology and biochemistry of various plant species. It is hypothesized that Pb-induced metabolic alterations could manifest as structural variations in the roots of plants. In light of this, the morphological, anatomical, and ultrastructural variations (through scanning electron microscopy, SEM) were studied in 4-day-old seedlings of Triticum aestivum grown under Pb stress (0, 8, 16, 40, and 80 mg Pb(2+) l(-1); mild to highly toxic). The toxic effect was more pronounced in radicle growth than on the plumule growth. The SEM of the root of T. aestivum depicted morphological alterations and surface ultrastructural changes. Compared to intact and uniform surface cells in the control roots, cells were irregular and desiccated in Pb(2+)-treated roots. In Pb(2+)-treated roots, the number of root hairs increased manifold, showing dense growth, and these were apparently longer. Apart from the deformity in surface morphology and anatomy of the roots in response to Pb(2+) toxicity, considerable anatomical alterations were also observed. Pb(2+)-treated root exhibited signs of injury in the form of cell distortion, particularly in the cortical cells. The endodermis and pericycle region showed loss of uniformity post Pb(2+) exposure (at 80 mg l(-1) Pb(2+)). The cells appeared to be squeezed with greater depositions observed all over the tissue. The study concludes that Pb(2+) treatment caused structural anomalies and induced anatomical and surface ultrastructural changes in T. aestivum.

Pb-inhibited mitotic activity in onion roots involves DNA damage and disruption of oxidative metabolism

Plant responses to abiotic stress significantly affect the development of cells, tissues and organs. However, no studies correlating Pb-induced mitotic inhibition and DNA damage and the alterations in redox homeostasis during root division per se were found in the literature. Therefore, an experiment was conducted to evaluate the impact of Pb on mitotic activity and the associated changes in the oxidative metabolism in onion roots. The cytotoxic effect of Pb on cell division was assessed in the root meristems of Allium cepa (onion). The mitotic index (MI) was calculated and chromosomal abnormalities were sought. Pb-treatment induced a dose-dependent decrease in MI in the onion root tips and caused mitotic abnormalities such as distorted metaphase, fragments, sticky chromosomes, laggards, vagrant chromosomes and bridges. Single Cell Gel Electrophoresis was also performed to evaluate Pb induced genotoxicity. It was accompanied by altered oxidative metabolism in the onion root tips suggesting the interference of Pb with the redox homeostasis during cell division. There was a higher accumulation of malondialdehyde, conjugated dienes and hydrogen peroxide, and a significant increase in the activities of superoxide dismutases, ascorbate peroxidases, guaiacol peroxidases and glutathione reductases in Pb-treated onion roots, whereas catalases activity exhibited a decreasing pattern upon Pb exposure. The study concludes that Pb-induced cytotoxicity and genotoxicity in the onion roots is mediated through ROS and is also tightly linked to the cell cycle. The exposure to higher concentrations arrested cell cycle leading to cell death, whereas different repair responses are generated at lower concentrations, thereby allowing the cell to complete the cell cycle.

Citronellol Disrupts Membrane Integrity by Inducing Free Radical Generation

Citronellol, an oxygenated monoterpene, is found naturally in the essential oils of several aromatic plants and has been reported to exhibit growth inhibitory and pesticidal activities. However, its mechanism of action is largely unexplored. We investigated the effect of citronellol, which is lipophilic in nature on membrane integrity in terms of lipid peroxidation, conjugated dienes content, membrane permeability, cell death, and activity of the enzyme lipoxygenase in roots of hydroponically grown wheat. Citronellol (50 - 250 μM) caused a significant inhibition of root and shoot growth. Furthermore, exposure to citronellol enhanced the solute leakage, increased the malondialdehyde content and lipoxygenase activity, and decreased the conjugated diene content. This indicates that citronellol induces generation of reactive oxygen species (ROS) resulting in lipid peroxidation and membrane damage. This was confirmed by in situ histochemical studies indicating cell death and disruption of membrane integrity. We conclude from this study that citronellol inhibits the root growth by ROS-mediated membrane disruption.

Cell Phone Radiations Affect Early Growth of Vigna radiata (Mung Bean) through Biochemical Alterations

The indiscriminate use of wireless technologies, particularly of cell phones, has increased the health risks among living organisms including plants. We investigated the impact of cell phone electromagentic fi eld (EMF) radiations (power density, 8.55 μW cm-2) on germination, early growth, proteins and carbohydrate contents, and activities of some enzymes in Vigna radiata. Cell phone EMF radiations signifi cantly reduced the seedling length and dry weight of V. radiata after exposure for 0.5, 1, 2, and 4 h. Furthermore, the contents of proteins and carbohydrates were reduced in EMF-exposed plants. However, the activities of proteases, α-amylases, β-amylases, polyphenol oxidases, and peroxidases were enhanced in EMF-exposed radicles indicating their role in providing protection against EMF-induced stress. The study concludes that cell phone EMFs impair early growth of V. radiata seedlings by inducing biochemical changes.

Lead (Pb)-induced biochemical and ultrastructural changes in wheat (Triticum aestivum) roots

The focus of the present study was to explore lead (Pb)-induced metabolic alterations vis-à-vis ultrastructural changes in wheat roots to establish Pb toxicity syndrome at a structural level. Pb (50-500 μM) enhanced malondialdehyde (an indicator of lipid peroxidation) and hydrogen peroxide content, and electrolyte leakage, thereby suggesting reactive oxygen species-induced disruption of membrane integrity and oxidative stress in wheat roots. The activities of superoxide dismutases and catalases enhanced upon Pb exposure, whereas those of ascorbate and guaiacol peroxidases declined. Pb-induced metabolic disruption was manifested in significant alterations in wheat root ultrastructure as analyzed by transmission electron microscopy. Pb caused thinning of cell wall (at 50 μM), formation of amoeboid protrusions and folds and intercellular spaces, and appearance of lesions and nicks/breaks (at ≥ 250 μM Pb). Pb was deposited along the cell walls as dark precipitates. At ≤ 250 μM Pb, the number of mitochondria increased significantly, whereas structural damage in terms of change of shape and disintegration was observed at ≥ 250 μM Pb. Pb reduced the size of nucleoli and induced puff formation (at 250 μM), resulting in complete disintegration/disappearance of nucleolus at 500 μM. The study concludes that Pb inhibited wheat root growth involving an ROS-mediated oxidative damage vis-à-vis the ultrastructural alterations in cell membrane and disruption of mitochondrial and nuclear integrity.

A time course assessment of changes in reactive oxygen species generation and antioxidant defense in hydroponically grown wheat in response to lead ions (Pb2+)

We examined the effect of Pb(2+) (8 and 40 mg l(-1)) on reactive oxygen species generation and alterations in antioxidant enzymes in hydroponically grown wheat at 24, 72, and 120 h after exposure. Pb(2+) toxicity was more pronounced on root growth, and it correlated with the greater Pb accumulation in roots. Pb exposure (40 mg l(-1)) enhanced superoxide anion, H(2)O(2), and MDA content in wheat roots by 1.9- to 2.2-folds, 56-255%, and 41-90%, respectively, over the control. Pb-induced loss of membrane integrity was confirmed by the enhanced electrolyte leakage and in vivo histochemical localization. Activities of scavenging enzymes, superoxide dismutases and catalases, enhanced in Pb-treated wheat roots by 1.4- to 5.7-folds over that in the control. In contrast, the activities of ascorbate and guaiacol peroxidases and glutathione reductases decreased significantly, suggesting their non-involvement in detoxification process. The study concludes that Pb(2+)-induced oxidative damage in wheat roots involve greater H(2)O(2) accumulation and the deactivation of the related scavenging enzymes.

Arsenic (As) inhibits radicle emergence and elongation in Phaseolus aureus by altering starch-metabolizing enzymes vis-à-vis disruption of oxidative metabolism

The present study investigated the effect of Arsenic (As; 5, 10, 50 μM) on protein and sugar metabolism vis-à-vis oxidative damage during early germination process and radicle emergence (at 12, 24 and 48 h stage) in Phaseolus aureus. As-exposure (50 μM) significantly enhanced protein content (by 40-60%), whereas carbohydrate content declined (by 31-44%) over that in the control. It was associated with a decline in the activities of proteases (47-53%), and increase in the activities of α- and β-amylases, starch phosphorylases, and acid invertases by 3.0, 2.6, 4.8, and 1.7 times after 48 h exposure to 50 μM As. The alteration in protein and carbohydrate metabolic machinery was also accompanied by As-induced reactive oxygen species (ROS)-mediated oxidative damage. As treatment enhanced malondialdehyde and hydrogen peroxide content by 46-252% and 23-216%, and hydroxyl and superoxide ion generation by 15-104% and 17-278%, respectively. As-induced lipid peroxidation and membrane disruption was confirmed by enhanced electrolyte leakage (by 49%) and reduced cell viability (by 43%). Furthermore, in response to 50 μM As, the activities of superoxide dismutases, catalases, ascorbate peroxidases, guaiacol peroxidases, and glutathione reductases increased by 77%, 70%, 116%, 43% and 120%, respectively, in radicles at 48 h stage over that in the control. The study concludes that As inhibits radicle emergence and elongation in germinating P. aureus seeds by altering biochemical processes related to sugar metabolism and inducing an ROS-mediated oxidative damage.

Cell phone electromagnetic field radiations affect rhizogenesis through impairment of biochemical processes

Indiscriminate adoption and use of cell phone technology has tremendously increased the levels of electromagnetic field radiations (EMFr) in the natural environment. It has raised the concerns among the scientists regarding the possible risks of EMFr to living organisms. However, not much has been done to assess the damage caused to plants that are continuously exposed to EMFr present in the environment. The present study investigated the biochemical mechanism of interference of 900 MHz cell phone EMFr with root formation in mung bean (Vigna radiata syn. Phaseolus aureus) hypocotyls, a model system to study rhizogenesis in plants. Cell phone EMFr enhanced the activities of proteases (by 1.52 to 2.33 times), polyphenol oxidases (by 1.5 to 4.3 times), and peroxidases (by 1.5 to 2.0 times) in mung bean hypocotyls over control. Further, EMFr enhanced malondialdehyde (an indicator of lipid peroxidation), hydrogen peroxide, and proline content, indicating a reactive oxygen species-mediated oxidative damage in hypocotyls. It was confirmed by the upregulation in the activities of antioxidant enzymes (superoxide dismutase, ascorbate peroxidase, guaiacol peroxidase, catalase, and glutathione reductase) suggesting their possible role in providing protection against EMFr-induced oxidative damage. The study concluded that cell phone radiations affect the process of rhizogenesis through biochemical alterations that manifest as oxidative damage resulting in root impairment.

Mobile phone radiation inhibits Vigna radiata (mung bean) root growth by inducing oxidative stress

During the last couple of decades, there has been a tremendous increase in the use of cell phones. It has significantly added to the rapidly increasing EMF smog, an unprecedented type of pollution consisting of radiation in the environment, thereby prompting the scientists to study the effects on humans. However, not many studies have been conducted to explore the effects of cell phone EMFr on growth and biochemical changes in plants. We investigated whether EMFr from cell phones inhibit growth of Vigna radiata (mung bean) through induction of conventional stress responses. Effects of cell phone EMFr (power density: 8.55 microW cm(-2); 900 MHz band width; for 1/2, 1, 2, and 4 h) were determined by measuring the generation of reactive oxygen species (ROS) in terms of malondialdehyde and hydrogen peroxide (H(2)O(2)) content, root oxidizability and changes in levels of antioxidant enzymes. Our results showed that cell phone EMFr significantly inhibited the germination (at > or =2 h), and radicle and plumule growths (> or =1 h) in mung bean in a time-dependent manner. Further, cell phone EMFr enhanced MDA content (indicating lipid peroxidation), and increased H(2)O(2) accumulation and root oxidizability in mung bean roots, thereby inducing oxidative stress and cellular damage. In response to EMFr, there was a significant upregulation in the activities of scavenging enzymes, such as superoxide dismutases, ascorbate peroxidases, guaiacol peroxidases, catalases and glutathione reductases, in mung bean roots. The study concluded that cell phone EMFr inhibit root growth of mung bean by inducing ROS-generated oxidative stress despite increased activities of antioxidant enzymes.

Essential oil of Artemisia scoparia inhibits plant growth by generating reactive oxygen species and causing oxidative damage

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 beta-myrcene (29.27%) as the major constituent followed by (+)-limonene (13.3%), (Z)-beta-ocimene (13.37%), and gamma-terpinene (9.51%). The oil and beta-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 beta-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 beta-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.

Phytotoxicity of volatile oil from Eucalyptus citriodora against some weedy species

A study was undertaken to explore the phytotoxicity of volatile essential oil from Eucalyptus citriodora Hook. against some weeds viz. Bidens pilosa, Amaranthus viridis, Rumex nepalensis, and Leucaena leucocephala in order to assess its herbicidal activity. Dose-response studies conducted under laboratory conditions revealed that eucalypt oils (in concentration ranging from 0.0012 to 0.06%) greatly suppress the germination and seedling height of test weeds. At 0.06% eucalypt oil concentration, none of the seed of test weeds germinated. Among the weed species tested, A. viridis was found to be the most sensitive and its germination was completed inhibited even at 0.03%. Not only the germination and seedling growth, even the chlorophyll content and respiratory activity in leaves of emerged seedlings were severely affected. In A. viridis chlorophyll content and respiratory activity were reduced by over 51% and 71%, respectively, even at a very low concentration of 0.06%. These results indicated an adverse effect of eucalypt oils on the photosynthetic and energy metabolism of the test weeds. A strong negative correlation was observed between the observed effect and the concentration of eucalypt oil. Based on the study, it can be concluded that oil from E. citriodora possess strong inhibitory potential against weeds that could be exploited for weed management.

2-Benzoxazolinone (BOA) induced oxidative stress, lipid peroxidation and changes in some antioxidant enzyme activities in mung bean (Phaseolus aureus)

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, 1.15.1.1), ascorbate peroxidase (APX, 1.11.1.11), guaiacol peroxidase (GPX, 1.11.1.7), catalase (CAT, 1.11.1.6) and glutathione reductase (GR, 1.6.4.2) in Phaseolus aureus (mung bean). BOA significantly enhanced malondialdehyde (MDA) content, a product of LP, in both leaves and roots of mung bean. The amount of H(2)O(2), a product of oxidative stress, and endogenous PRO increased many-fold in response to BOA. Accumulation of PRO, MDA and H(2)O(2) indicates the cellular damage in the target tissue caused by ROS generated by BOA. In response to BOA, there was a significant increase in the activities of scavenging enzymes SOD, APX, GPX, CAT, and GR in root and leaf tissue of mung bean. At 5 mM BOA, GR activity in roots showed a nearly 22-fold increase over that in control. The present study concludes that BOA induces oxidative stress in mung bean through generation of ROS and upregulation of activities of various scavenging enzymes.

Antifungal activity of the volatile oil of Eucalyptus citriodora

The volatile oil extracted from the leaves of Eucalyptus citriodora showed a wide spectrum of antifungal activity.