Potential allelopatic effects of stilbenoids and flavonoids from leaves of Carex distachya Desf.

The potential allelopathic effects of 14 stilbenoids and five flavonoids, isolated from leaves of Carex distachya Desf., were evaluated on the seed germination and seedling growth of three coexisting Mediterranean species (Dactylis hispanica, Petrorhagia velutina, and Phleum subulatum). The structures of the metabolites have been elucidated on the basis of their spectroscopic features (1D and 2D NMR experiments and EI–MS and ESI–MS data). The bioassays showed species-specific effects of the metabolites from C. distachya, specially on the plant growth (root and shoot elongation) which resulted significantly stimulated or inhibited at 10⁻⁴ M concentration. The effects on root elongation is generally greater than the shoot growth at all the tested concentrations (10⁻⁴–10⁻⁸ M). Cluster of biological data showed interesting relationships between the chemical structures of the compounds and their biological effects.     

An allelopathic investigation of the domination of the introduced invasive Conyza canadensis L.

The introduced, invasive species Conyza canadensis L. covers large areas of the sandy levees next to the River Tamiš (Serbia), forming dense microcomplexes and dominating the other herbaceous species in the ruderal phytocoenosis with its aboveground mass and abundance. In addition to this species, a further 28 plant species were found, but the abundance and cover of these was significantly lower. The allelopathic influence of the species C. canadensis was investigated through analyzing the total phenolics and phenolic acids, as the main allelochemicals, in dead and vegetative parts and the soil beneath them. Seed germination and seedling growth of the target plants (Dactylis glomerata L. and Trifolium repens L.), which grow in this community, served as a measure of the inhibitory capacity of this species. It was established that the content of total phenolics and phenolic acids (p-coumaric, ferulic, p-hydroxybenzoic, vanillic and syringic) varies, following the order: vegetative plant parts > dead plant parts > sandy soil under C. canadensis. Water leachate and soils inhibited seed germination and seedling growth of the test plants to varying degrees, following the order: vegetative parts > dead parts > sandy soil, which is directly related to the content of total phenolics and phenolic acids in them. It was concluded that the pioneer species C. canadensis plays a decisive role in the first phases of vegetation succession and the process of soil formation on the barren sandy levees, owing to the synthesis of secondary phenolic metabolites.     

云雾山铁杆蒿茎叶浸提液对封育草地四种优势植物的化感效应

为了揭示铁杆蒿群落在植被演替中的作用,通过研究铁杆蒿茎叶浸提液对铁杆蒿草地4种优势植物(百里香、大针茅、本氏针茅和赖草)的种子萌发及幼苗生长的干扰,结果表明:高浓度的铁杆蒿浸提液(甲醇浸提液和水浸提液)使得百里香、大针茅、本氏针茅和赖草的种子发芽指数降低,发芽率、芽长和根长低于对照,种子平均发芽时间延长达1.13-2.16 d。而低浓度浸提液(0.005 g/mL)使得百里香的发芽要高于对照11.63%(水浸提液)、15.12%(甲醇浸提液)。在幼苗生长期,铁杆蒿浸提液对4种受试植物幼苗芽和根的生长受到不同程度的抑制,不同浓度的浸提液对植物的化感作用强度不同,随浓度的增加,抑制作用越强,0.1 g/mL相对其他浓度有显著性差异;其中0.005 g/mL浸提液对本氏针茅和赖草的幼苗生长有促进作用,幼根生长高出对照19.00%、16.06%,水浸提液对幼芽促进了2.33%、9.06%,在0.1 g/mL浓度下,本氏针茅或大针茅的生长完全受到抑制,芽长和根长抑制率为100%;同一浓度下的不同浸提液对植物的抑制作用也不同,其中百里香对铁杆蒿浸提液的敏感度是最低的;甲醇浸提液的化感作用要强于水浸提液。在封育过程中,百里香群落向铁杆蒿群落的过渡,铁杆蒿的化感作用是该草地演替的一个重要影响因子。     

栎属7种植物种子的发芽抑制物质研究

运用系统溶剂法和生物测定法,以栎属7种植物种子为材料,研究了其种皮、胚(胚及周围部分子叶)和子叶(远离胚端2/3子叶)1.0 g/mL和0.5 g/mL浓度甲醇等浸提液以及各有机相对白菜种子萌发的影响。结果表明:栓皮栎、锐齿栎、蒙古栎、沼生栎和麻栎甲醇浸提液均能显著降低白菜种子发芽率、根长和苗高,且对发芽率的抑制作用逐渐降低;夏栎和房山栎甲醇浸提液对白菜种子发芽率没有显著影响,但对根长和苗高有一定的抑制作用;种子不同部位甲醇浸提液的抑制作用表现为胚>子叶>种皮,且甲醇高浓度浸提液的抑制作用大于低浓度的抑制作用;甲醇相对白菜种子发芽率、苗高或根长的抑制作用最强,其次是乙酸乙酯相,其它溶剂相萃取液的抑制作用不明显。栎属种子甲醇浸提液及各有机相对白菜种子苗高和根长的抑制作用强于对发芽率的影响,说明栎属种子中所含抑制物质主要是限制自身根和芽的生长,可能是造成延迟萌发和出苗不整齐的原因。     

Growth,biomass allocation,and autofragmentation responses to root and shoot competition in Myriophyllum spicatum as a function of sediment nutrient supply

Plant growth, biomass allocation and autofragmentation were investigated in response to root and shoot competition in the submersed macrophyte Myriophyllum spicatum L. growing in two sediment environments. Biomass accumulation and allocation were significantly affected by sediment fertility, with a higher total biomass observed in fertile sediment (average: 4.69 g per plant vs. 1.12 g per plant in infertile sediment). Root-to-shoot ratios were 0.34 and 0.06 in the infertile and fertile sediments, respectively, reflecting the high investment placed on roots under infertile conditions. In the presence of root, shoot, and full competition, whole plant biomass decreased by 18%, 12% and 24% in the infertile sediments, and 23%, 25% and 33% in the fertile sediments, respectively. Root weight ratios (RWRs) increased with root competition by 38% (P < 0.001) and 12% (P = 0.002), while leaf weight ratios (LWRs) decreased with shoot competition by 6% (P = 0.042) and 5% (P = 0.001) in the infertile and fertile sediments, respectively. A total of 406 autofragments were harvested in the fertile sediments, but none were obtained from the infertile sediments. In the control, autofragment number and biomass was 166% and 175% higher compared to the competition treatment. Root and shoot competition resulted in a 21% (P = 0.043) and 18% (P = 0.098) decrease in the autofragment biomass, respectively. These results indicated that M. spicatum responds to different sediment fertility by changing its allocation patterns. Moreover, both root and shoot competition influenced plant growth and autofragmentation, while sediment nutrient availability played an important role in M. spicatum autofragmentation.     

Isolation and identification of a plant growth inhibitor from Tinospora tuberculata Beumee

Tinospora tuberculata Beumee has been used widely as a folk medicine and several bioactive compounds have been isolated. However, no herbicidal compound has been reported in this species. Therefore, we investigated the presence of phytotoxins in T. tuberculata. The aqueous methanol extracts of T. tuberculata inhibited the growth of roots and shoots of cress (Lepidum sativum L.), lettuce (Lactuca sativa L.), timothy (Phleum pratense L.) and barnyard grass (Echinochloa crus-galli (L.) Beauv.). The extract was then purified by several chromatographic runs with monitoring the inhibitory activity and the main phytotoxic substance was isolated. The chemical structure of the compound was determined by spectral data as syringin (4-[(1E)-3-Hydroxyprop-1-en-1-yl]-2,6-dimethoxyphenyl β-d-glucopyranoside). It inhibited the root and shoot growth of all test plant species at concentrations >10 µM. The concentrations required for 50 % inhibition of root and shoot growth of cress and lettuce ranged from 78.2 to 412 μM, and that of timothy and barnyard grass renged from 9.8 to 73.2 µM. Effectiveness of syringin on monocotyledonous (timothy and barnyard grass) plants was greater than that on dicotyledonous (cress and lettuce) plants. These results suggest that syringin may contribute to the allelopathic effect caused by the T. tuberculata extract.     

Chemical composition and larvicidal activity of essential oils from Piper species

The larvicidal activity of essential oils of four species of Piper from the Amazon Forest was tested using third-instar larvae of Aedes aegypti. The oils were extracted by steam distillation and analyzed by GC and GC–MS. The main components isolated from each Piper species were as follows: viridiflorol (27.50%), aromadendrene (15.55%) and β-selinene (10.50%) from Piper gaudichaudianum; β-selinene (15.77%) and caryophyllene oxide (16.63%) from Piper humaytanum; dillapiol (54.70%) and myristicin (25.61%) from Piper permucronatum; and asaricin (27.37%) and myristicin (20.26%) from Piper hostmanianum. Amongst all essential oils tested, the most active against larvae of A. aegypti was the oil extracted from P. permucronatum, with a LC₅₀ = 36 μg/ml (LC₉₀ = 47 μg/ml), followed by the essential oil of P. hostmanianum, with a LC₅₀ = 54 μg/ml (LC₉₀ = 72 μg/ml). The oils with higher content of arylpropanoids were more active against larvae of A. aegypti.     

Inhibition of Candida albicans biofilm formation and yeast-hyphal transition by 4-hydroxycordoin

Candida albicans distinguishing features such as dimorphism and biofilm formation are thought to play a key role in oral tissue invasion and resistance to host defences and antifungal agents. In this study, we investigated the effect of 4-hydroxycordoin, a natural isopentenyloxychalcone, on growth, biofilm formation and yeast-hyphal transition of C. albicans. Serial dilutions of 4-hydroxycordoin in YNB medium were prepared in microplates to determine minimal inhibitory concentrations (MIC) and effects on biofilm formation for two strains of C. albicans. 4-Hydroxycordoin at up to 200 μg/ml had no effect on growth of C. albicans. Biofilm formation was strongly inhibited (>85%) by 4-hydroxycordoin at 20 μg/ml, while concentrations ranging from 50 to 200 μg/ml caused a significant inhibition of yeast-hyphal transition, as determined by microscopic observation. In conclusion, 4-hydroxycordoin exerts inhibitory effects on two important virulence factors of C. albicans: biofilm formation or yeast-hyphal transition. This suggests that 4-hydroxycordoin may have a therapeutic potential for C. albicans infections.     

Cadmium accumulation in Atriplex halimus subsp. schweinfurthii and its influence on growth,proline, root hydraulic conductivity and nutrient uptake

Atriplex halimus subsp. schweinfurthii is a newly found cadmium (Cd)-hyperaccumulator, but there have been no detailed studies on its physiological responses when Cd is hyperaccumulated. A. halimus was grown in hydroponic conditions to investigate the effect of cadmium chloride (CdCl₂) on growth, water status, leaf chlorophyll concentration, proline and Cd accumulation. Treatments were prepared by adding 0, 50, 100, 200 and 400 μM CdCl₂ to the nutrient medium. Plant growth was significantly affected at high-Cd treatments. Increased CdCl₂ decreased chlorophyll concentration, transpiration and root hydraulic conductivity (L₀). Hence water flux had only a little effect on the uptake of Cd in A. halimus seedlings. In contrast, proline content increased with increasing CdCl₂ concentration. Plants accumulated substantial amount of Cd in different plant parts (shoot and root). Most of the Cd taken up was retained in roots (606.51 μg g⁻¹DW after 15 d at 400 μM CdCl₂). The addition of Cd in the culture medium affected calcium (Ca) and potassium (K) nutrition in both shoot and root. A. halimus provides a new plant resource for exploring the mechanism of Cd hyperaccumulation and has potential for use in the phytostabilization of Cd-contaminated salt soils.     

Inhibition of development, swarming differentiation and virulence factors in Proteus mirabilis by an extract of Lithrea molleoides and its active principle (Z,Z)-5-(trideca-4’,7’-dienyl)-resorcinol

Antibacterial activity of Lithrea molleoides extract against Proteus mirabilis has been previously reported by our group. In the present study, the compound (Z,Z)-5-(trideca-4’,7’-dienyl)-resorcinol (1) was isolated as its responsible active principle. The effects of the compound obtained and of L. molleoides extract on P. mirabilis growth and virulence factors were evaluated.Compound 1 showed MIC and MBC values of 4000 μg/ml. It was found that the extract, at four times the MIC, produced complete killing of the uropathogen at 2 h from the beginning of the experiment, while the alkylresorcinol, at four times the MIC, produced the same effect after 24 h. Hemolysis was adversely affected in treatments with both products at 8 μg/ml, while hemagglutination was not altered. The whole extract induced complete autoaggregation of P. mirabilis at 2000 μg/ml, while compound 1 at the same concentration did not show this property. Swarming motility was delayed in treatments with the extract and with 1 at 1000 and 8 μg/ml, respectively, at 8 h from the beginning of the assay. Complete inhibition of the phenomenon was still observed after 24 h when compound 1 was added at 125 μg/ml.These findings offer the possibility of new classes of antimicrobial medicines to tackle infections caused by P. mirabilis.     

Micropropagation of Romulea minutiflora, Sisyrinchium laxum and Tritonia gladiolaris — Iridaceae with ornamental potential

Three species of the Iridaceae with ornamental potential were micropropagated with the intention of producing propagules more rapidly for possible commercialization. Shoot induction from in vitro germinated seedlings of Romulea minutiflora was obtained with 5.4 μM α-naphthaleneacetic acid (NAA) and 23.2 μM kinetin. Shoot explants formed corms best with 3.4 or 17 μM paclobutrazol, and one incidence of in vitro flowering was observed. Sisyrinchium laxum shoot explants produced more and healthier multiple shoots with meta-topolin (mT) than with 6-benzyladenine (BA). Rooting was best in control (no hormone) cultures, and addition of NAA and indole-3-acetic acid (IAA) inhibited root formation and growth of shoot explants, and formed short, stunted roots. Roots produced by indole-3-butyric acid (IBA) were morphologically most similar to those produced in control cultures. Liquid-shake culture of shoots did not lead to meristemoid formation, despite supplementation with various growth regulators (mT, GA₃ or paclobutrazol). Low temperature (10-20 °C) induced corm formation in Tritonia gladiolaris shoot cultures, while corm formation was completely inhibited above 20 °C. Increasing temperature from 10 °C to 15 °C and from 15 °C to 20 °C increased corm mass significantly. Paclobutrazol (3.4 μM), GA₃ (2.9 μM), NAA (5.4 μM ) or methyl jasmonate (4.5 μM ) could not induce corm formation at 25 °C, while at 15 °C, NAA and methyl jasmonate inhibited corm formation. These experiments successfully demonstrate the ease with which different genera of the Iridaceae can be multiplied in in vitro systems.     

Sorgoleone,a sorghum root exudate: Algicidal activity and acute toxicity to the ricefish Oryzias latipes

The discovery of natural and natural-based compounds has resulted in its application as an alternative to synthetic algicides to control harmful algae in aquatic systems. Of the many natural-product-based algicides, sorgoleone, a natural plant product from Sorghum bicolor root exudates has been investigated for its controlling effect on different algal species and its acute fish toxicity. Growth of the blue green algal species Microcystis aeruginosa Kützing was completely inhibited by the crude methanol extract of sorghum root at 20 μg mL⁻¹. The most noticeable inhibition was observed in the bioassay of n-hexane soluble extract, where 98% growth inhibition occurred in M. aeruginosa at the concentration of 1.25 μg mL⁻¹. Sorgoleone very effectively controlled blue green algae inhibiting 97% of M. aeruginosa at 0.5 μg mL⁻¹ and 99% of Anabaena affinis Lemmermann at 4 μg mL⁻¹. In contrast, inhibition of the green algae species Chlorella vulgaris Beijerinck and Scenedensmus spp. at 16 μg mL⁻¹ sorgoleone was 87 and 68%, respectively. There were no mortalities or adverse effects observed in any of the fish exposed to water control, solvent control, and a nominal concentration of 1 μg mL⁻¹ during the test period. The no observed effect concentration (NOEC) value was 1.5 μg mL⁻¹ for the tested fish (O. latipes). Sorgoleone can be considered as an effective and an ecologically and environmentally sustainable approach to controlling harmful algae.     

Nematicidal activity of Haplophyllum tuberculatum and Plectranthus cylindraceus oils against Meloidogyne javanica

The potentials of Haplophyllum tuberculatum and Plectranthus cylindraceus oils to control Meloidogyne javanica were investigated in vitro and in a greenhouse. A mixture of Haplophyllum and Plectranthus oils (1:1) was highly toxic to M. javanica in vitro, as it killed all nematode juveniles and inhibited hatching of eggs at 12.5 μg/ml concentration after 24 h exposure time, as did carbofuran at the same concentration. In the green-house, tomatoes grown in soil treated with a combination (1:1) of the two oils developed fewer root galls than those grown in soil treated with higher doses of either oil. The oil mixture, at 2.5 and 5.0 μg/ml of soil, was not phytotoxic to tomato plants as evident from the appearance and height of plants after 12 weeks exposure time, compared to treatment over the same period at lower effective doses. The nematicidal activity of the combined essential oils was suggested by the presence of C₁₀ dienes, C₁₀ trienes and C₁₀ phenol.     

Influence of Pericarp,Cotyledon and Inhibitory Substances on Sharp Tooth Oak (Quercus aliena var. acuteserrata) Germination

In order to explore the mechanism of delayed and uneven germination in sharp tooth oak (Quercus aliena var. acuteserrata) (STO), mechanical scarification techniques were used to study STO root and shoot germination and growth. The techniques used were: removing cup scar (RS), removing the pericarp (RP), and cutting off 1/2 (HC) and 2/3 (TC) cotyledons. Germination percentage and root and shoot length for Chinese cabbage (Beassica pekinensis) seeds (CCS) were also investigated for CCS cultivated in a Sanyo growth cabinet watered by distilled water and 80% methanol extracts from the acorn embryo, cotyledon and pericarp with concentrations of 1.0 g, 0.8 g, 0.6 g and 0.4 g dry acorn weight per ml methanol. The results showed that the majority of roots and shoots from acorns with RP and HC treatment emerged two weeks earlier, more simultaneously, and their total emergences were more than 46% and 28% higher, respectively. TC accelerated root and shoot emergence time and root length, but root and shoot germination rate and shoot height had no significant difference from the control. Positive consequences were not observed on all indices of RS treatment. The germination rates of CCS watered by 1.0 g·ml⁻¹ methanol extracts from the embryo and cotyledon were significantly lower than those from the pericarp, and all concentrations resulted in decreased growth of root and shoot. Methanol extracts from pericarp significantly reduced root length of CCS, but presented little response in germination percentage and shoot length. The inhibitory effect was gradually increased with the increasing concentration of the methanol extract. We conclude that both the mechanical restriction of the pericarp and the presence of germination inhibitors in the embryo, cotyledon and pericarp are the causes for delayed and asynchronous germination of STO acorns.     

A novel allelopathic substance, 13-epi-orthosiphol N,in Orthosiphon stamineus

Orthosiphon stamineus (Java tea) has been widely used as traditional herb and several bioactive compounds against animal cells have been isolated. However, no bioactive compound against plants has been reported. Therefore, we investigated possible allelopathic properties and substances in O. stamineus. Aqueous methanol extracts of O. stamineus inhibited root and hypocotyl growth of cress (Lepidium sativum) and lettuce (Lactuca sativa) seedlings. Increasing the extract concentration increased the inhibition, which suggests that O. stamineus may have allelopathic properties. When the extract was divided into an ethyl acetate and an aqueous fraction, the ethyl acetate fraction showed the stronger inhibitory effect. Thus, the ethyl acetate phase was further purified, and the main allelopathic substance was isolated and identified as 13-epi-orthosiphol N, a novel compound, by spectral data. 13-epi-Orthosiphol N inhibited root and hypocotyl growth of cress and lettuce at concentrations greater than 10 μmol/L. The concentrations required for 50% inhibition ranged from 41 to 102 μmol/L. These results suggest that 13-epi-orthosiphol N may be an allelochemical and main contributor to the growth inhibitory effect of O. stamineus and may have potential as a template for the development of new plant control substances.     

冷蒿对三种禾本科植物种子萌发和幼苗生长的化感作用

研究了冷蒿茎叶水浸提液及冷蒿斑块土壤对羊草草原3种禾本科植物(羊草、克氏针茅和糙隐子草)种子萌发及幼苗生长的影响.结果表明:冷蒿茎叶水浸提液使受试植物种子的发芽指数降低,平均发芽时间延长.羊草、克氏针茅和糙隐子草幼苗苗高及克氏针茅幼苗根长均受冷蒿茎叶水浸提液抑制;浸提液浓度≥0.075g.ml-1时显著抑制羊草幼苗根长生长,≤0.05g.ml-1时则无显著影响;而茎叶水浸提液对糙隐子草幼苗根长有"低促高抑"的作用.冷蒿斑块土壤抑制受试植物幼苗生长;3种植物对冷蒿化感效应的敏感性依次为克氏针茅羊草糙隐子草,且幼苗根长的敏感性均大于苗高.     

Anticancer effect of Tamarix gallica extracts on human colon cancer cells involves Erk1/2 and p38 action on G2/M cell cycle arrest

Taking into account that oxidative stress is among the factors causing cancer-related death; chemoprevention which consists in using antioxidant substances such as phenolics could prevent cancer formation and progression. In the present study, phenolic contents and antioxidant activities of methanolic extracts from the halophyte Tamarix gallica shoots were determined. Moreover, the anticancer effect of this species on human colon cancer cells and the likely underlying mechanisms were also investigated. Shoot extracts showed an appreciable total phenolic content (85 mg GAE/g DW) and a high antioxidant activity (IC₅₀ = 3.3 μg/ml for DPPH test). At 50 and 100 μg/ml, shoot, leaf, and flower extracts significantly inhibited Caco-2 cell growth. For instance, almost all plant part extracts inhibited cell growth by 62 % at the concentration 100 μg/ml. DAPI staining results revealed that these extracts decrease DNA synthesis and confirm their effect on Caco-2 cells proliferation, principally at 100 μg/ml. More importantly, cell mitosis was arrested at G₂/M phase. The changes in the cell-cycle-associated proteins (cyclin B1, p38, Erk1/2, Chk1, and Chk2) are correlated with the changes in cell cycle distribution. Taken together, our data suggest that T. gallica is a promising candidate species to be used as a source of anticancer biomolecules.     

Eurycomanone suppresses expression of lung cancer cell tumor markers, prohibitin, annexin 1 and endoplasmic reticulum protein 28

Bioactive compounds from the medicinal plant, Eurycoma longifolia Jack have been shown to promote anti-proliferative effects on various cancer cell lines. Here we examined the effects of purified eurycomanone, a quassinoid found in Eurycoma longifolia Jack extract, on the expression of selected genes of the A549 lung cancer cells. Eurycomanone inhibited A549 lung cancer cell proliferation in a dose-dependent manner at concentrations ranging from 5 to 20 μg/ml. The concentration that inhibited 50% of cell growth (GI₅₀) was 5.1 μg/ml. The anti-proliferative effects were not fully reversible following the removal of eurycomanone, in which 30% of cell inhibition still remained (p < 0.0001, T-test). At 8 μg/ml (GI₇₀), eurycomanone suppressed anchorage-independent growth of A549 cells by >25% (p < 0.05, T-test, n = 8) as determined using soft agar colony formation assay. Cisplatin, a chemotherapy drug used for the treatment of non small cell lung cancer on the other hand, inhibited A549 cells proliferation at concentrations ranging from 0.2 μg/ml to 15 μg/ml with a GI₅₀ of 0.58 μg/ml. The treatment with eurycomanone reduced the abundance expression of the lung cancer markers, heterogeneous nuclear ribonucleoprotein (hnRNP) A2/B1, p53 tumor suppressor protein and other cancer-associated genes including prohibitin (PHB), annexin 1 (ANX1) and endoplasmic reticulum protein 28 (ERp28) but not the house keeping genes. The mRNA expressions of all genes with the exception of PHB were significantly downregulated, 72 h after treatment (p < 0.05, T-test, n = 9). These findings suggest that eurycomanone at viable therapeutic concentrations of 5-20 μg/ml exhibited significant anti-proliferative and anti-clonogenic cell growth effects on A549 lung cancer cells. The treatment also resulted in suppression of the lung cancer cell tumor markers and several known cancer cell growth-associated genes.