Effect of leaf water extracts of four Asteraceae alien invasive plants on germination performance of Lactuca sativa L. under acid deposition

Plant Ecology - Allelopathy of alien invasive plants (AIP) on plant germination performance is essential for their successful invasion. However, the allelopathy of AIP may be reformed or even...     

ssDNA Aptamer Specifically Targets and Selectively Delivers Cytotoxic Drug Doxorubicin to HepG2 Cells

Hepatocellular carcinoma (HCC) is the third leading cause of death due to cancer worldwide with over 500,000 people affected annually. Although chemotherapy has been widely used to treat patients with HCC, alternate modalities to specifically deliver therapeutic cargos to cancer cells have been sought in recent years due to the severe side effects of chemotherapy. In this respect, aptamer-based tumor targeted drug delivery has emerged as a promising approach to increase the efficacy of chemotherapy and reduce or eliminate drug toxicity. In this study, we developed a new HepG2-specific aptamer (HCA#3) by a procedure known as systematic evolution of ligands by exponential enrichment (SELEX) and exploited its role as a targeting ligand to deliver doxorubicin (Dox) to HepG2 cells in vitro. The selected 76-base nucleotide aptamer preferentially bound to HepG2 hepatocellular carcinoma cells but not to control cells. The aptamer HCA#3 was modified with paired CG repeats at the 5′-end to carry and deliver a high payload of intercalated Dox molecules at the CG sites. Four Dox molecules (mol/mol) were fully intercalated in each conjugate aptamer-Dox (ApDC) molecule. Biostability analysis showed that the ApDC molecules are stable in serum. Functional analysis showed that ApDC specifically targeted and released Dox within HepG2 cells but not in control cells, and treatment with HCA#3 ApDC induced HepG2 cell apoptosis but had minimal effect on control cells. Our study demonstrated that HCA#3 ApDC is a promising aptamer-targeted therapeutic that can specifically deliver and release a high doxorubicin payload in HCC cells.     

Drought may be beneficial to the competitive advantage of Amaranthus spinosus

干旱利于刺苋的竞争优势 干旱可以影响入侵植物的生长和土壤酶活性。因此,非常有必要评估干旱背景下入侵植物的竞争优势以及入侵植物和干旱对土壤酶活性的影响。本研究旨在分析干旱背景下起源于热带美洲的入侵植物刺苋(Amaranthus spinosus)与本地植物苋菜(Amaranthus tricolor)共存时的竞争优势和土壤酶活性。通过栽植实验进行刺苋与苋菜的竞争共栽培,并进行不同水平的干旱处理,即：(i)对照;(ii)轻度干旱;(iii)重度干旱。实验结束后测定两种苋属植物的功能性状、渗透调节、抗氧化酶活性以及土壤pH、电导率、土壤微生物生物量碳含量和土壤酶活性。干旱背景下,刺苋的相对竞争强度和相对优势度均高于苋菜。因此,干旱利于刺苋的竞争优势。干旱背景下,刺苋的土壤水溶性盐含量和蔗糖水解能力均大于苋菜。而较高的土壤水溶性盐含量和蔗糖水解能力利于刺苋对养分的获取和利用。     

Exploring the stereochemistry of CXCR4-peptide recognition and inhibiting HIV-1 entry with D-peptides derived from chemokines

Chemokine receptor CXCR4 plays an important role in the immune system and the cellular entry of human immunodeficiency virus type 1 (HIV-1). To probe the stereospecificity of the CXCR4-ligand interface, d-amino acid peptides derived from natural chemokines, viral macrophage inflammatory protein II (vMIP-II) and stromal cell-derived factor-1alpha (SDF-1alpha), were synthesized and found to compete with (125)I-SDF-1alpha and monoclonal antibody 12G5 binding to CXCR4 with potency and selectivity comparable with or higher than their l-peptide counterparts. This was surprising because of the profoundly different side chain topologies between d- and l-enantiomers, which circular dichroism spectroscopy showed adopt mirror image conformations. Further direct binding experiments using d-peptide labeled with fluorescein (designated as FAM-DV1) demonstrated that d- and l-peptides shared similar or at least overlapping binding site(s) on the CXCR4 receptor. Structure-activity analyses of related peptide analogs of mixed chiralities or containing alanine replacements revealed specific residues at the N-terminal half of the peptides as key binding determinants. Acting as CXCR4 antagonists and with much higher biological stability than l-counterparts, the d-peptides showed significant activity in inhibiting the replication of CXCR4-dependent HIV-1 strains. These results show the remarkable stereochemical flexibility of the CXCR4-peptide interface. Further studies to understand the mechanism of this unusual feature of the CXCR4 binding surface might aid the development of novel CXCR4-binding molecules like the d-peptides that have high affinity and stability.     

Transgenerational changes in the genome stability and methylation in pathogen-infected plants: (virus-induced plant genome instability)

Previously, we reported the generation of a virus-induced systemic signal that increased the somatic and meiotic recombination rates in tobacco mosaic virus (TMV)-infected tobacco plants. Here, we analyzed the progeny of plants that received the signal and found that these plants also have a higher frequency of rearrangements in the loci carrying the homology to LRR region of the gene of resistance to TMV (N-gene). Analysis of the stability of repetitive elements from Nicotiana tabacum loci and 5.8S ribosomal RNA loci did not show any changes. Further analysis of the changes in the progeny of infected plants revealed that they had substantially hypermethylated genomes. At the same time, loci-specific methylation analysis showed: (1) profound hypomethylation in several LRR-containing loci; (2) substantial hypermethylation of actin loci and (3) no change in methylation in the loci of repetitive elements from N. tabacum or 5.8S ribosomal RNA. Global genome hypermethylation of the progeny is believed to be part of a general protection mechanism against stress, whereas locus-specific hypomethylation is associated with a higher frequency of rearrangements. Increased recombination events combined with the specific methylation pattern induced by pathogen attack could be a sign of an adaptive response by plants.     

水稻种衣剂对秧苗生理生化及叶绿素荧光参数的影响

以‘深两优5814’水稻种子为试验材料,用2.5%吡·咪、3%恶·咪、锐胜和适乐时分别包衣种子,测定水稻幼苗抗氧化酶活性、MDA含量、GSH含量、叶绿素含量和叶绿素荧光参数,探讨种衣剂对幼苗的胁迫机理,为种衣剂的安全高效应用提供理论依据。结果表明:(1)种衣剂能提高水稻幼苗的抗氧化酶活性,播种后14d,2.5%吡·咪和锐胜处理组叶片的SOD活性上升,3%恶·咪处理组叶片的POD活性上升;播种后22d,2.5%吡·咪和3%恶·咪处理组叶片的CAT活性上升;播种后26d,锐胜和适乐时处理组叶片的CAT活性上升;2.5%吡·咪和3%恶·咪显著提高了播种后22d叶片的MDA含量。4种种衣剂均能提升幼苗叶片GSH含量,并以3%恶·咪的提升效果最为明显。(2)4种种衣剂均能降低叶绿素含量,但随培养时间的延长叶片内叶绿素含量逐渐恢复到正常水平。(3)4种种衣剂对水稻叶片最大光化学效率φPo无显著影响,吸光性能指数PIABS值也未呈下降趋势,比活性参数ABS/CSM值随培养时间的延长出现下降趋势,其中以3%恶·咪处理组下降最为明显;同时,3%恶·咪处理组叶片的热耗散DIo/CSM值也显著高于对照。研究认为,各种衣剂对水稻幼苗生长造成了一定的胁迫,但水稻自身防御体系能有效缓解农药胁迫作用,种衣剂的使用处于安全水平,但3%恶·咪的胁迫较严重,使用效果较差。     

Distinct functional sites for human immunodeficiency virus type 1 and stromal cell-derived factor 1alpha on CXCR4 transmembrane helical domains

The entry of human immunodeficiency virus type 1 (HIV-1) into the cell is initiated by the interaction of the viral surface envelope protein with two cell surface components of the target cell, CD4 and a chemokine coreceptor, usually CXCR4 or CCR5. The natural ligand of CXCR4 is stromal cell-derived factor 1alpha (SDF-1alpha). Whereas the overlap between HIV-1 and SDF-1alpha functional sites on the extracellular domains of CXCR4 has been well documented, it has yet to be determined whether there are sites in the transmembrane (TM) helices of CXCR4 important for HIV-1 and/or SDF-1alpha functions, and if such sites do exist, whether they are overlapping or distinctive for the separate functions of CXCR4. For this study, by employing alanine-scanning mutagenesis, (125)I-SDF-1alpha competition binding, Ca(2+) mobilization, and cell-cell fusion assays, we found that the mutation of many CXCR4 TM residues, including Tyr(45), His(79), Asp(97), Pro(163), Trp(252), Tyr(255), Asp(262), Glu(288), His(294), and Asn(298), could selectively decrease HIV-1-mediated cell fusion but not the binding activity of SDF-1alpha. Phe(87) and Phe(292), which were involved in SDF-1alpha binding, did not play a significant role in the coreceptor activity of CXCR4, further demonstrating the disconnection between physiological and pathological activities of CXCR4 TM domains. Our data also show that four mutations of the second extracellular loop, D182A, D187A, F189A, and P191A, could reduce HIV-1 entry without impairing either ligand binding or signaling. Taken together, our first detailed characterization of the different functional roles of CXCR4 TM domains may suggest a mechanistic basis for the discovery of new selective anti-HIV agents.