The effect of pH on the lability of lead and cadmium sorbed on humic acid particles

Abstract

Sorption of lead(II) or cadmium(II) ions on humic acid particles (at pH 3.5) yields surface complexes which are sparingly soluble in the pH 3.55 region. Interaction of these species with acetic acid or dilute nitric acid released ASV labile metal species (mainly hydrated metal ion). When the pH was adjusted between 4 and 7, increasing amounts of the metal humate species (and humic acid substrate) dissolved and low levels of ASV labile species were detected. Overnight interaction with an excess of acetate ions (0.01 M) led to higher lability values (attributed to acetate/humate ligand exchange). The percentage of labile metal ion detected in acetate solutions varied with the amount of metal ion initially sorbed (range 100 to 500 mmol g^?1). With the lower loadings, the ASV labile levels peaked in the pH 6–7 region (at around 12% of total sorbed cadmium, and 4% of total lead). In alkaline solutions, the percentage of labile Cd fell to about half of the peak value, but with Pb, lability values increased at pH > 8, due possibly to the formation of hydroxy complex species. The ASV lability of the Cd and Pb humates, and their 24 hour lability values (determined using a transfer to cation exchanger technique) has been compared with the behaviour of Cu and Zn humates (using similar conditions).     

Metabolic profile and antioxidant responses during drought stress recovery in sugarcane treated with humic acids and endophytic diazotrophic bacteria

Water deficit is the major yield‐limiting factor for sugarcane crop production that can be enhanced by inoculating with plant growth promoting bacteria (PGPB) combined with humic substances. The aim of this work was to examine changes to the metabolic profile and antioxidant enzyme activity of sugarcane treated with PGPB and humic acid (HA) after drought and then rehydration. The drought was imposed by withholding irrigation for 21 days thereby measuring enzyme activity, metabolic profile and photosynthetic rate 1 week after rehydratation. Growth of plants treated with HA, PGPB and with both treatments combined (PGPB + HA) was higher than control plants. The antioxidant enzymes superoxide dismutase (SOD), catalase (CAT) and ascorbate peroxidase (APX) activities remained higher after rehydration only in plants treated with HA. Plants treated with HA and PGPB + HA exhibited increased transpiration, stomatal conductance and net photosynthesis than plants treated with PGPB. The PGPB‐treated plants exhibited drought resistance that resembled ‘delayed stress onset’, which is a new term for preserving water in the plants tissues. Water preservation in plants treated with PGPB was corroborated by higher relative water content (RWC) than control plants at the end of the drought period. Plants treated with HA + PGPB exhibited the highest water potential after rehydration and high RWC. Osmotic adjustment in the other treatments (control, HA and PGPB) was indicated by a new pattern of metabolic response after rehydration, including generally enhanced carbohydrates and proteins and specific changes induced by HA‐enhancing aromatic compounds, whereas PGPB exhibited enhanced fatty acids and other aliphatic H species. Humic acids assist with drought stress recovery by inducing antioxidant enzyme activity whereas PGPB induced preservation of leaf water potential and RWC by closing stomata efficiently, resulting in plant water preservation.     

Bacterial biofilms and quorum sensing: fidelity in bioremediation technology

Increased contamination of the environment with toxic pollutants has paved the way for efficient strategies which can be implemented for environmental restoration. The major problem with conventional methods used for cleaning of pollutants is inefficiency and high economic costs. Bioremediation is a growing technology having advanced potential of cleaning pollutants. Biofilm formed by various micro-organisms potentially provide a suitable microenvironment for efficient bioremediation processes. High cell density and stress resistance properties of the biofilm environment provide opportunities for efficient metabolism of number of hydrophobic and toxic compounds. Bacterial biofilm formation is often regulated by quorum sensing (QS) which is a population density-based cell–cell communication process via signaling molecules. Numerous signaling molecules such as acyl homoserine lactones, peptides, autoinducer-2, diffusion signaling factors, and α-hydroxyketones have been studied in bacteria. Genetic alteration of QS machinery can be useful to modulate vital characters valuable for environmental applications such as biofilm formation, biosurfactant production, exopolysaccharide synthesis, horizontal gene transfer, catabolic gene expression, motility, and chemotaxis. These qualities are imperative for bacteria during degradation or detoxification of any pollutant. QS signals can be used for the fabrication of engineered biofilms with enhanced degradation kinetics. This review discusses the connection between QS and biofilm formation by bacteria in relation to bioremediation technology.     

外源激素对马尾松花芽分化及内源物质的影响

为探讨马尾松球花形成与植物激素水平的关系,该研究对贵州省都匀无性系种子园11年生马尾松进行不同浓度的 IAA、IBA、GA3、BAP等植物激素处理,采用考马斯亮蓝G-250染色法、蒽酮法分别对不同浓度不同激素处理后的枝条上针叶中的可溶性蛋白质和可溶性糖含量变化进行测定,并在第二年开花时对试验枝条的开花情况进行了调查。结果表明：在8－11月份,进行500 mg·L-1的BAP 处理有利于马尾松雌球花和雄球花的形成,100 mg·L-1的GA3处理有利于马尾松雌球花的形成;而GA3250 mg·L-1和GA3500 mg·L-1处理有利于马尾松雄球花的形成,IAA 250 mg·L-1对马尾松雌雄球花同枝的数量有提高作用。在10－11月份,对马尾松进行500 mg·L-1的BAP、IAA、GA3处理后,马尾松针叶内蛋白质含量变化有显著影响;在10月份时,进行BAP 100 mg·L-1处理后,其可溶性糖含量及可溶性蛋白含量均可达到极显著水平。而在8月份与10月份时,分别进行IBA 100 mg·L-1与IBA 250 mg·L-1处理后,其可溶性蛋白含量与其对照差异处于极显著水平;在11月份时,进行GA3100 mg·L-1处理后,其可溶性蛋白含量与其对照差异处于极显著水平;而在11月份时,进行IBA 500 mg·L-1处理后,其可溶性蛋白含量与对照差异处于显著水平。     

内生真菌司氏角担子菌B6对尖孢镰刀菌西瓜专化型菌株的拮抗作用

近年来,尽管西瓜产业不断发展壮大,但轮作土壤种植西瓜易产生枯萎病害导致世界范围内的西瓜严重减产。通过对峙培养实验和抑菌实验探讨了重阳木内生真菌司氏角担子菌(Ceratobasidum stevensii)B6菌株对西瓜枯萎病病原菌尖孢镰刀菌西瓜专化型(Fusarium oxysporum f. sp.Niveum,FON)的拮抗作用,并初步分析了其作用机制。平板拮抗试验的结果表明,内生真菌B6生长过程中不是通过产生抑菌带来抑制FON菌丝,而是利用自身的生长优势将FON完全覆盖。显微观察B6与FON菌丝的接触部位,发现FON菌丝外侧附着B6顶端菌丝形成的胞样结构,表明FON菌丝生长仅受到B6菌丝的抑制。抑菌试验结果显示,B6产生的挥发性物质可以抑制FON的生长和产孢,并使其菌丝分枝明显减少;B6的发酵液对FON的生长和产孢没有抑制作用。因此,推测B6主要通过释放某些挥发性物质产生拮抗作用而抑制FON的生长。     

5种外源物质对干旱胁迫下笔筒树幼苗生长的缓解效应北大核心CSCD

为探究外源物质对干旱胁迫下笔筒树生长的缓解效应和生理机制,对实验室培养的笔筒树幼苗进行了自然干旱胁迫,期间分别叶面喷施1.0 mmol/L水杨酸(SA)、150μmol/L褪黑素(MT)、100 mg/L多效唑(PP_(333))、2.5 mmol/L氯化钙(CaCl_(2))以及0.3 mg/L的2,4-表油菜素内酯(EBR)溶液,测定各处理幼苗的生长和光合作用、抗氧化酶、渗透调解物质等相关生理指标。结果表明:(1)与正常生长对照(CK)相比,干旱胁迫(DCK)显著抑制笔筒树幼苗地上部分的生长,但能够显著促进地下部分的生长;干旱胁迫显著抑制笔筒树叶片抗氧化酶活性,加剧对细胞膜的损害,进而引起幼苗叶片相对电导率和丙二醛含量显著上升,显著增加渗透调节物质的积累;干旱胁迫也使叶片叶绿素含量显著降低,不能正常进行光合作用,其净光合速率、气孔导度和蒸腾速率都显著降低。(2)与DCK处理相比,叶面喷施外源物质可以显著提高笔筒树幼苗叶片抗氧化酶活性,有效清除细胞内过多的活性氧,显著降低相对电导率和丙二醛含量,使细胞膜系统代谢正常,减轻干旱胁迫对笔筒树幼苗造成的伤害,并提高净光合速率、气孔导度、蒸腾速率和叶绿素含量,有效减轻干旱胁迫对光合作用的抑制。(3)隶属函数法综合评价表明,适宜浓度的水杨酸(SA)和褪黑素(MT)处理对笔筒树幼苗干旱胁迫的缓解效应最好。     

First demonstration of the neuroepithelial cells and their chemical code in the accessory respiratory organ and the gill of the sharptooth catfish,Clarias gariepinus: A preliminary study

Available studies that have examined O₂ sensing in fish have indicated that oxygen-sensitive neuroepithelial cells (NECs) are O₂ sensors in the gills and initiate cardiorespiratory reflexes in aquatic vertebrates. This is the first study describing the occurrence of NECs in accessory respiratory organs in the air-breathing catfish Clarias gariepinus. Immunocytochemical stainings with specific neuronal markers such as nNOS, VAchT, 5-HT and TH have been shown to be very useful for location and distribution of these cells in the gill fans and suprabranchial chamber that take origin from the transformation of the gill tissue. But the response of these putative O₂ chemoreceptors, their role in the respiratory reflexes and their innervation await investigation.     

Recent advancement in the discovery and development of COX-2 inhibitors: Insight into biological activities and SAR studies (2008–2019)

Cyclooxygenase-2 is a very important physiological enzyme playing key roles in various biological functions especially in the mechanism of pain and inflammation, among other roles, making it a molecule of high interest to the pharmaceutical community as a target. COX 2 enzyme is induced only during inflammatory processes or cancer and reflects no role in the guarding stomach lining. Thus, selective COX-2 inhibition can significantly reduce the adverse effects including GI tract damage and hepatotoxic effects of traditional NSAIDs like aspirin, ibuprofen, etc. Recent developments on COX-2 inhibitors is primarily focused on improving the selectivity index of the drug towards COX-2 along with enhancing the potency of the drug by modifying the scaffolds of Coxibs currently in the market like Celecoxib, Indomethacin, Oxaprozin, etc. We have reported the progress on new COX-2 inhibitors in the last decade (2008–2019) focussing on five heterocyclic rings- Pyrazole, Indole, Oxazole, Pyridine and Pyrrole. The addition of various moieties to these core rings and their structure-activity relationship along with their molecular modelling data have been explored in the article. This review aims to aid medicinal chemists in the design and discovery of better COX-2 inhibitors constructed on these five heterocyclic pharmacophores.     

Quorum sensing: an emerging link between temperature and membrane biofouling in membrane bioreactors

Lab-scale membrane bioreactors (MBRs) were investigated at 12, 18, and 25?°C to identify the correlation between quorum sensing (QS) and biofouling at different temperatures. The lower the reactor temperature, the more severe the membrane biofouling measured in terms of the transmembrane pressure (TMP) during filtration. More extracellular polymeric substances (EPSs) that cause biofouling were produced at 18?°C than at 25?°C, particularly polysaccharides, closely associated with QS via the production of N-acyl homoserine lactone (AHL). However, at 12?°C, AHL production decreased, but the release of EPSs due to deflocculation increased the soluble EPS concentration. To confirm the temperature effect related to QS, bacteria producing AHL were isolated from MBR sludge and identified as Aeromonas sp., Leclercia sp., and Enterobacter sp. through a 16S rDNA sequencing analysis. Batch assays at 18 and 25?°C showed that there was a positive correlation between QS through AHL and biofilm formation in that temperature range.