Recent advances in application and progress of advanced materials as adsorbents in sample preparation for plant growth regulators.

Plant growth regulators are a class of physiologically active substances that could modify or regulate basic physiological processes in the plant and defense against abiotic and biotic stresses, including natural plant growth regulators and synthetic ones. Different from natural plant growth regulators with low content and high cost of extraction in plants, synthetic ones can be produced in large-scale production and widely used in agriculture for increasing and securing yield and quality of the harvested produce. However, like pesticides, the abuse of plant growth regulators will have negative impacts on human beings. Therefore, it is important to monitor plant growth regulators residues. Due to the low concentration of plant growth regulators and complex matrices of food, it is necessary to isolate and extract plant growth regulators by appropriate adsorbents in sample preparation for obtaining satisfactory results. In the last decade, several advanced materials as adsorbents have shown superiority in sample preparation. This review briefly introduces the recent application and progress of advanced materials as adsorbents in sample preparation for extraction of plant growth regulators from the complex matrix. In the end, the challenge and outlook about the extraction of plant growth regulators of these advanced adsorbents in sample preparation are presented.

Purification, characterization and antioxidant activities of a polysaccharide from the roots of Lilium davidii var. unicolor Cotton.

A polysaccharide (LPR) was separated from the roots of Lilium davidii var. unicolor Cotton with hot water extraction, ethanol precipitation, and purification by anion-exchange and gel-permeation chromatography. LPR was characterized. The weight-average molecular weight (MW) of LPR was 5.12 × 104 g/moL. Glucose and mannose comprised LPR with a molar ratio of 2.9:3.3. IR, NMR and methylation analysis showed that LPR was a natural O-acetyl glucomannan, the backbone mainly contained ß-(1 → 4)-linked d-glucopyranosyl and ß-(1 → 4)-linked D-mannopyanosyl, and the branches probably linked at O-2 and/or O-3 of the mannosyl and glucosyl residues. The acetyl groups mainly attached at O-2 or O-3 of mannosyl residues. X-ray diffractometric (XRD) analysis and scanning electron microscopy (SEM) analysis revealed that LPR was a semi-crystalline substance with porous lamellar structure. Bioassays in vitro indicated that LPR had distinct scavenging activities on hydroxyl radical and DPPH radical. These findings provided a reference for functional underutilization roots of L. davidii as natural antioxidant in food and pharmaceutical industry.

Structural characterization, antioxidant and antibacterial activities of two heteropolysaccharides purified from the bulbs of Lilium davidii var. unicolor Cotton.

Two heteropolysaccharides, BHP-1 and BHP-2, were separated and purified from the edible bulbs of Lilium davidii var. unicolor Cotton by anion-exchange and gel-permeation chromatography. The primary structural characteristics of BHP-1 and BHP-2 were investigated by Congo red test, X-ray diffractometry (XRD) analysis, IR, GC and NMR. The results showed that the weight-average molecular weight (MW) and number-average molecular weight (Mn) of BHP-1 and BHP-2 were nearly 1.93 × 105 g/moL, 8.86 × 104 g/moL and 3.52 × 104 g/moL, 2.95 × 104 g/moL, respectively. Glucose and mannose comprised BHP-1 in a relative molar ratio of 5.9:2.0, and BHP-2 was consisted of glucose, galactose, mannose and arabinose with approximate molar ratios of 8.3:1.5:1.0:1.1. Their backbone mainly contained α-(1 → 4)-linked d-glucopyranosyl. In addition, the C-6 of the glucose and C-2 of mannose residue of BHP-1 and BHP-2 were substituted. The two polysaccharides were semi-crystalline substance with multi-branching structure and triple helix conformation. Bioassays showed that BHP-1 and BHP-2 had effective antioxidant activities evaluated by DPPH, scavenging superoxide radical and OH radical in a dose-dependent manner. The two heteropolysaccharides also displayed distinct and selective antibacterial activity against B. cereus, P. putida, M. luteus and K. pneumonia with inhibition zones of 13 mm, 16 mm, 17 mm, 23 mm and 12 mm, 17 mm, 19 mm, 20 mm, respectively. These findings provided a reference for potential applications of the polysaccharides from L. davidii as natural antioxidants and antibacterial agents in food and pharmaceuticals.

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

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

Bio-guided isolation of plant growth regulators from allelopathic plant-Codonopsis pilosula: phyto-selective activities and mechanisms.

Natural pesticides are the subject of growing interest, as the overuse of synthetic pesticides severely threatens the safety of humans and the eco-environment. Allelopathic plants can release plentiful secondary metabolites as natural plant growth regulators to affect the growth of neighboring plants. Bio-guided isolation of the aerial waste part of typical allelopathic plant-Codonopsis pilosula led to six active compounds being produced, including ginsenoside Rg1 (1), ginsenoside Re (2), luteolin (3), luteolin-5-O-glucoside (4), ginsenoside Rb1 (5) and lobetyolin (6). Ginsenosides and luteolin-5-O-glucoside were firstly found in Codonopsis. Phyto-activity tests showed that all compounds showed inhibiting effects toward C. pilosula, and compounds 2, 4, 5 and 6 were also inhibitors of Amaranthus retroflexus. By contrast, the compounds promoted the seedling growth of wheat, rice and Setaria viridis. At certain concentrations, compounds 1, 4, 5 and 1, 2, 4 could observably promote the growth of wheat and rice seedlings, respectively, exceeding Setaria viridis. The different effects toward the two weeds might be related to the different ROS levels induced by the compounds. The ROS amounts in the root tips of S. viridis were as low as those in the control test, and the ROS content in the root tips increased with aggravation of the inhibition effect. In summary, successful isolation of phyto-selective chemicals from allelopathic plants may provide a promising method for natural herbicide screening. The compounds isolated could potentially be applied as inhibitors of dicotyledon weeds and promoters of monocotyledon crops for weed management in agriculture.

Structural basis, chemical driving forces and biological implications of flavones as Cu(II) ionophores.

A main biochemical property of cancer cells, compared with normal cells, is altered redox status including increased levels of copper to maintain their malignant phenotypes. Thus, increasing copper accumulation, by using ionophores, to disrupt abnormal redox homeostasis of cancer cells may be an important anticancer strategy. Naturally occurring molecules with extraordinarily diverse chemical scaffolds are an important source of inspiration for developing copper ionophores. Dietary flavonoids are well-characterized copper chelators and show cancer chemopreventive potential, but their ionophoric role for redox-active copper and the related biological implications have remained unknown. This study reports, for the first time, the structural basis, chemical driving forces and biological implications of flavones (a widely distributed subgroup of flavonoids) as Cu(II) ionophores, and also provides new insights into cancer chemopreventive mechanism of flavones bearing 3(or 5)-hydroxy-4-keto group. 3-Hydroxyflavone surfaced as a potent Cu(II) ionophore to induce the mitochondria-dependent apoptosis of cancer cells in a redox intervention fashion via sequential proton-loss Cu(II) chelation, GSH-driving releasing of copper and protonation-dependent efflux of the neutral ligand.

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

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

Antifungal activity of umbelliferone derivatives: Synthesis and structure-activity relationships.

Umbelliferone was an important allelochemical with a wide spectrum bioactivity. In our previous study, C7 hydroxy in the backbone of umbelliferone was identified to be responsible for its phytotoxicity and the targeted modification of the above site could lead to the phytotoxicity loss. In view of this, a series of hydroxycoumarins and C7 O-substituted umbelliferone derivatives were efficiently synthesized to evaluate their antifungal activity against four phytopathogenic fungi. Most of them, as we predicted, exhibited improved fungicidal activity. The phytotoxicity of effective compounds was also assayed by Lactuca sativa to investigate their side effects on plant growth. Compounds 9 and 17 were identified to show strong antifungal activity with low phytotoxicity. A brief investigation on structure-activity relationships revealed that the modification at the C7 hydroxy of umbelliferone could be a promising way to enhance the antifungal activity with decreasing the phytotoxicity.

Cycloartane-type triterpenoids from Astragalus hoantchy French.

A new cycloartane-type triterpenoid, 3ß-acetoxy-9ß,19-cyclolanost-24E-ene-1α,16ß-diol-27-O-ß-d-glucopyranoside (1), together with three known ones (2-4) were isolated from the aerial parts of Astragalus hoantchy. The structure of compound 1 was elucidated by detailed spectroscopic analyses including 1D and 2D NMR, HRESIMS, and IR experiments. All of the four compounds were isolated from A. hoantchy for the first time. The antifungal activities of compounds 1-4 against a phytopathogenic fungus (Alternaria solani) were evaluated with the result that compound 3 exhibited a moderate activity with an IC50 value of 284 µg/mL.

Flavoniods from aerial parts of Astragalus hoantchy.

Four new flavonoids, astragaisoflavans A-D (1-4), along with thirteen known ones (5-17) were isolated from the aerial parts of Astragalus hoantchy. Their structures were established by the extensive spectroscopic analyses including one- and two-dimensional NMR, HRESIMS, IR, and UV results. The absolute configurations of 1-4 were deduced based on circular dichroism. Compounds 1-3 all possessed a rare modified A-ring and compound 4 was a dimeric isoflavan. Compound 5 was first identified from genus Astragalus and 6-17 were found from A. hoantchy for the first time. Compound 1 and 4 were evaluated for their antifungal activity against Alternaria solani (a phytopathogenic fungus), with the result that 1 failed to exhibit significant antifungal activity at the testing concentration of 100µg/mL and the IC50 value of 4 was 173.3µg/mL.

Characterization of rhizosphere and endophytic fungal communities from roots of Stipa purpurea in alpine steppe around Qinghai Lake.

Stipa purpurea is among constructive endemic species in the alpine steppe on the Qinghai-Xizang Plateau. To reveal the fungal community structure and diversity in the rhizosphere and roots of this important grass and to analyze the potential influence of different habitats on the structure of fungal communities, we explored the root endophyte and the directly associated rhizosphere communities of S. purpurea by using internal transcribed spacer rRNA cloning and sequencing methods. We found that the roots of S. purpurea are associated with a diverse consortium of Basidiomycota (59.8%) and Ascomycota (38.5%). Most fungi obtained from rhizosphere soil in S. purpurea have been identified as Ascomycetes, while the high proportion detected in roots were basidiomycetous endophytes. The species richness, diversity, and evenness of fungal assemblages were higher in roots than in the rhizosphere soil. Fungi inhabiting the rhizosphere and roots of S. purpurea are significantly different, and the rhizosphere and endophyte communities are largely independent with little overlap in the dominant phyla or operational taxonomic units. Taken together, these results suggested that a wide variety of fungal communities are associated with the roots and rhizosphere soil of S. purpurea and that the fungal assemblages are strongly influenced by different habitats.

Synthesis of N-substituted phthalimides and their antifungal activity against Alternaria solani and Botrytis cinerea.

As organosulfur and organophosphorus agents, phaltane and phosmet are facing great challenges for the environmental contamination, mammalian toxicity and increasing resistance with long term use. It is efficient and meaningful to develop phthalimide-based alternatives with non-sulfur and non-phosphorus groups. A series of N-substituted phthalimides were synthesized and their antifungal activity against two disastrous phytopathogenic fungi, Alternaria solani and Botrytis cinerea was evaluated in vitro. Most of them showed significant antifungal activity against both of fungi, or either of them selectively. N-vinylphthalimide (4) and 8-[4-(phthalimide-2-yl) butyloxy] quinoline (13) were identified as the most promising candidates against B. cinerea and A. solani with the IC50 values of 7.92 µg/mL and 10.85 µg/mL respectively. The brief structure-activity relationships have revealed that vinyl, quinolyl, bromide alkyl and benzyl substitutions were appropriate substituents and coupling functional moieties indirectly with optimum alkyl chain was efficient to prepare phthalimides related fungicides.

Allelochemicals from the Rhizosphere Soil of Cultivated Astragalus hoantchy.

Astragalus hoantchy, a widely cultivated medicinal plant species in traditional Chinese and Mongolian medicine, has been often hampered by replant failure during cultivation, like many other herbs of the genus Astragalus. Root aqueous extracts of Astragalus herbs were reported to exhibit allelopathic activity against other plants and autotoxic activity on their own seedlings, but the allelochemicals released by Astragalus plants have not been specified so far. Ten compounds were isolated from the rhizosphere soil extract of cultivated A. hoantchy and elucidated by spectroscopic analysis. Compounds 1-6 observably showed allelopathic activity against Lactuca sativa seedlings and autotoxic activity against A. hoantchy seedlings. The isolated compounds were further confirmed and quantified by high-performance liquid chromatography (HPLC) in the rhizosphere soil, with a total concentration of 9.78 µg/g (dry weight). These results specify and verify the allelochemicals released by cultivated A. hoantchy into the soil environment, which may provide new insights into the allelopathic mechanisms of this medicinal plant and probably assist in clarifying the replant problems of Astragalus plants.

Phytotoxicity of umbelliferone and its analogs: Structure-activity relationships and action mechanisms.

Two coumarins, umbelliferone and daphnoretin, were isolated from roots of Stellera chamaejasme L; the former had been identified as one of the main allelochemicals in our previous studies. Both of them have the skeleton of 7-hydroxycoumarin, but showed different phytotoxic effects. Umbelliferone and its analogs were then prepared to investigate the structure-activity relationship of hydroxycoumarins and screened for phytotoxicity. The inhibitory effects varied observably in response to the coumarin derivatives, especially umbelliferone (1), 7-hydroxy-4-methylcoumarin (3) and coumarin (10) displayed strong inhibition of lettuce and two field weeds, Setaria viridis and Amaranthus retroflexus, and compounds 11 and 12 also exhibited phytotoxic activity with species specificity. The number and location of hydroxyl groups were importantly responsible for the phytotoxicity. A C7 hydroxyl group was considered to be a potentially active site and methyl substitution at the C4 position contributed significantly to the activity. The phytotoxic mechanism was briefly studied with umbelliferone by evaluating the reactive oxygen species (ROS) and chlorophylls level in lettuce seedlings. The results showed that umbelliferone induced the accumulation of ROS in the root tip and significantly decreased the chlorophyll content in the leaves. Thus, a ROS-mediated regulation pathway and the inhibition of photosynthesis were definitely involved in the phytotoxicity of umbelliferone.

Isolation, Identification, and Autotoxicity Effect of Allelochemicals from Rhizosphere Soils of Flue-Cured Tobacco.

Autotoxicity, defined as a deleterious allelopathic effect among individuals of the same plant species, is considered as one of the factors that contributes to replant failure. Tobacco, as an important cultured and economic crop over the world, has been often hampered by replant failure. In view of the seriousness of this problem, the allelochemicals of flue-cured tobacco and their allelopathic effects were investigated. The extracts of rhizosphere soil exhibited phytotoxic activities against Lactuca sativa and autotoxic activities against tobacco itself. Bioassay-guided fractionation of the extract led to the isolation of six compounds, the structures of which were elucidated by spectroscopic analysis. Among them, ß-cembrenediol (1), di-n-hexyl phthalate (2), and bis(2-propylheptyl) phthalate (3) showed observably phytotoxic activities against L. sativa seedlings and autotoxic activities on tobacco. The allelochemicals were then verified in the root zone soils of flue-cured tobacco by high-performance liquid chromatography (HPLC). These results provide new insights into the allelopathic mechanisms involved in the replant failure of flue-cured tobacco.

Phylogenic diversity and tissue specificity of fungal endophytes associated with the pharmaceutical plant, Stellera chamaejasme L. revealed by a cultivation-independent approach.

The fungal endophytes associated with medicinal plants have been demonstrated as a reservoir with novel natural products useful in medicine and agriculture. It is desirable to explore the species composition, diversity and tissue specificity of endophytic fungi that inhabit in different tissues of medicinal plants. In this study, a culture-independent survey of fungal diversity in the rhizosphere, leaves, stems and roots of a toxic medicinal plant, Stellera chamaejasme L., was conducted by sequence analysis of clone libraries of the partial internal transcribed spacer region. Altogether, 145 fungal OTUs (operational taxonomic units), represented by 464 sequences, were found in four samples, of these 109 OTUs (75.2 %) belonging to Ascomycota, 20 (13.8 %) to Basidiomycota, 14 (9.7 %) to Zygomycota, 1 (0.7 %) to Chytridiomycota, and 1 (0.7 %) to Glomeromycota. The richness and diversity of fungal communities were strongly influenced by plant tissue environments, and the roots are associated with a surprisingly rich endophyte community. The endophyte assemblages associated with S. chamaejasme were strongly shaped by plant tissue environments, and exhibited a certain degree of tissue specificity. Our results suggested that a wide variety of fungal assemblages inhabit in S. chamaejasme, and plant tissue environments conspicuously influence endophyte community structure.

Isolation and characterization of bacteria from the rhizosphere and bulk soil of Stellera chamaejasme L.

This study is the first to describe the composition and characteristics of culturable bacterial isolates from the rhizosphere and bulk soil of the medicinal plant Stellera chamaejasme L. at different growth stages. Using a cultivation-dependent approach, a total of 148 isolates showing different phenotypic properties were obtained from the rhizosphere and bulk soil. Firmicutes and Actinobacteria were the major bacterial groups in both the rhizosphere and bulk soil at all 4 growth stages of S. chamaejasme. The diversity of the bacterial community in the rhizosphere was higher than that in bulk soil in flowering and fruiting stages. The abundance of bacterial communities in the rhizosphere changed with the growth stages and had a major shift at the fruiting stage. Dynamic changes of bacterial abundance and many bacterial groups in the rhizosphere were similar to those in bulk soil. Furthermore, most bacterial isolates exhibited single or multiple biochemical activities associated with S. chamaejasme growth, which revealed that bacteria with multiple physiological functions were abundant and widespread in the rhizosphere and bulk soil. These results are essential (i) for understanding the ecological roles of bacteria in the rhizosphere and bulk soil and (ii) as a foundation for further evaluating their efficacy as effective S. chamaejasme growth-promoting rhizobacteria.

Allelochemicals in the rhizosphere soil of Euphorbia himalayensis.

Weed infestation has been known to cause considerable reductions in crop yields, thereby hindering sustainable agriculture. Many plants in genus Euphorbia affect neighboring plants and other organisms by releasing chemicals into the environment. In view of the serious threat of weeds to agriculture, the allelochemicals of Euphorbia himalayensis and their allelopathic effects were investigated. The extract of root exudates from rhizosphere soil exhibited allelopathic activities against crops (wheat, rape, and lettuce) and grasses (Poa annua, Festuca rubra, and red clover). Bioassay-guided fractionation and isolation from the root extract of E. himalayensis led to the characterization of two ellagic acid derivatives and a jatrophane diterpene, which observably showed phytotoxic activities against lettuce, Festuca arundinacea, and F. rubra. They were further confirmed by ultra-performance liquid chromatography-tandem mass spectrometry to have concentrations of 3.6, 3.8, and 8.99 nmol/g in the rhizospere soil, respectively. Bioassay indicated that the combination of the allelochemicals could be selective plant growth regulator in agriculture.

Influence of side chain structure changes on antioxidant potency of the [6]-gingerol related compounds.

[6]-Gingerol and [6]-shogaol are the major pungent components in ginger with a variety of biological activities including antioxidant activity. To explore their structure determinants for antioxidant activity, we synthesized eight compounds differentiated by their side chains which are characteristic of the C1-C2 double bond, the C4-C5 double bond or the 5-OH, and the six- or twelve-carbon unbranched alkyl chain. Our results show that their antioxidant activity depends significantly on the side chain structure, the reaction mediums and substrates. Noticeably, existence of the 5-OH decreases their formal hydrogen-transfer and electron-donating abilities, but increases their DNA damage- and lipid peroxidation-protecting abilities. Additionally, despite significantly reducing their DNA strand breakage-inhibiting activity, extension of the chain length from six to twelve carbons enhances their anti-haemolysis activity.