Role of Melatonin in Plant Tolerance to Soil Stressors: Salinity,pH and Heavy Metals

Melatonin (MT) is a pleiotropic molecule with diverse and numerous actions both in plants and animals. In plants, MT acts as an excellent promotor of tolerance against abiotic stress situations such as drought, cold, heat, salinity, and chemical pollutants. In all these situations, MT has a stimulating effect on plants, fomenting many changes in biochemical processes and stress-related gene expression. Melatonin plays vital roles as an antioxidant and can work as a free radical scavenger to protect plants from oxidative stress by stabilization cell redox status; however, MT can alleviate the toxic oxygen and nitrogen species. Beyond this, MT stimulates the antioxidant enzymes and augments antioxidants, as well as activates the ascorbate–glutathione (AsA–GSH) cycle to scavenge excess reactive oxygen species (ROS). In this review, we examine the recent data on the capacity of MT to alleviate the effects of common abiotic soil stressors, such as salinity, alkalinity, acidity, and the presence of heavy metals, reinforcing the general metabolism of plants and counteracting harmful agents. An exhaustive analysis of the latest advances in this regard is presented, and possible future applications of MT are discussed.     

High-molar mass acrylamide-co-diacetoneacrylamide graft copolymers as viscosity enhancer for polymer flooding oil recovery

One of the most widely applied enhanced oil recovery processes is the polymer flooding, in which aqueous solution of polymer viscosifier is introduced in oil reservoirs to increase the recuperation of the remaining oil. From the current challenges of this process, it can be referred to a high cost of materials regarding their substantially required amount and the low impact on the mobility ratio during the process due to the reduction of solution viscosity at high temperatures and high salinity environments. The purpose of this study is to investigate the concept of acrylamide-based thermosassociating copolymer (TAP), with a specific morphology and chemistry (hydrophilic main backbone made of polyacrylamide with grafted amide functionalized pending chains) as viscosity enhancer at harsh conditions of high temperature and salinity. For that aim, a specific TAP microstructure was targeted (very high molar mass linear polymer chains with improved copolymer homogeneity). It is achieved in this study throughout applying the reaction engineering approach, such as synthesis in semi-batch mode or/and in heterogeneous dispersed media. As a result, the synthesized TAP presented excellent behavior as viscosity enhancer especially under high temperature and salinity conditions with improved performance in comparison to TAP synthesized by a conventional solution polymerization approach and to actual commercial high molar mass acrylamide-based polymer.     

外源水杨酸对水稻(Oryza sativa L.)幼苗根的NaCl胁迫缓解效应

为研究25mg／L外源水杨酸对0，50，100mmol／L NaCl处理下水稻幼苗根的胁迫缓解效应，测定了根组织内脯氨酸含量、可溶性糖含量、氨同化关键酶活性等相关指标．结果表明外源水杨酸可使组织内脯氨酸含量显著降低至与正常对照相当水平，而可溶性糖含量升高，说明外源水杨酸存在时可溶性糖作为主要渗透胁迫调节物并对盐胁迫适当缓解，表现在幼苗根谷氨酰胺合成酶及依赖于NADH的谷氨酸脱氢酶的活性上升20％左右、可溶性蛋白质含量的提高，氮同化加强而对盐胁迫有一定的抗性．对50mmol／L NaCl胁迫处理的材料缓解效应较显著．     

海水盐度和温度实时检测的新型光纤传感器研究

提出了一种新颖的用于海水温度和盐度同时实时探测的光纤传感器系统。分别利用半导体材料吸收光谱的临界极限值随温度变化发生移动而导致出射光强改变的特性和待测液体盐度变化引起传输光折射角改变导致接收端光线偏移的性质，通过反射式的结构设计和线阵排列的接收光纤信号传输至海面以上，并由CCD实现对光强峰值信号及其偏移量的采集。传感器由一直角棱镜、本征GaAs单晶体薄片、装有参考液和待测液的水槽、接收光纤阵列等部分组成。理论分析和仿真结果验证了传感器设计的可行性。     

K+ uptake by root systems grown in soil under salinity: I. A mathematical model

A novel theoretical model is proposed for K⁺ uptake by intact root systems from saline soil considering interactions with Na⁺, Ca²⁺ and Mg²⁺. The model assumes radial movement of ions towards the root governed by advection and diffusion flux mechanisms, and chemical exchange of the four cations according to Gapon isotherms, with Cl^? as the accompanying anion. Influx of K⁺ to the root surface is assumed as a function of its concentration in the soil solution at the root. This influx is governed by a saturable-cooperative term and a linear term for low and high K⁺ concentrations, respectively. Influx of Na⁺, above a critical value of its concentration, increases linearly with its concentration in the soil solution at the root surface. Uptake of Ca^{+ 2+} is controlled by the balance between influxes of anions and cations, which induces efflux of H⁺ or HCO ₃ ^? , and interacts with calcite in a calcareous soil. The model may provide information about the behavior of ions at the root-soil interface which cannot be measuredin situ.     

Production of Plant Beneficial and Antioxidants Metabolites by Klebsiella variicola under Salinity Stress

Bacteria that surround plant roots and exert beneficial effects on plant growth are known as plant growth-promoting rhizobacteria (PGPR). In addition to the plant growth-promotion, PGPR also imparts resistance against salinity and oxidative stress and needs to be studied. Such PGPR can function as dynamic bioinoculants under salinity conditions. The present study reports the isolation of phytase positive multifarious Klebsiella variicola SURYA6 isolated from wheat rhizosphere in Kolhapur, India. The isolate produced various plant growth-promoting (PGP), salinity ameliorating, and antioxidant traits. It produced organic acid, yielded a higher phosphorous solubilization index (9.3), maximum phytase activity (376.67 ± 2.77 U/mL), and copious amounts of siderophore (79.0%). The isolate also produced salt ameliorating traits such as indole acetic acid (78.45 ± 1.9 µg/mL), 1 aminocyclopropane-1-carboxylate deaminase (0.991 M/mg/h), and exopolysaccharides (32.2 ± 1.2 g/L). In addition to these, the isolate also produced higher activities of antioxidant enzymes like superoxide dismutase (13.86 IU/mg protein), catalase (0.053 IU/mg protein), and glutathione oxidase (22.12 µg/mg protein) at various salt levels. The isolate exhibited optimum growth and maximum secretion of these metabolites during the log-phase growth. It exhibited sensitivity to a wide range of antibiotics and did not produce hemolysis on blood agar, indicative of its non-pathogenic nature. The potential of K. variicola to produce copious amounts of various PGP, salt ameliorating, and antioxidant metabolites make it a potential bioinoculant for salinity stress management.     

A numerical modelling study of the flow and salinity structure in the Godavari Estuary,east coast of India

The Godavari Estuary in Andhra Pradesh (a state bordering the east coast of India) communicates with the Bay of Bengal. Conditions in the estuary are characterized by a seasonally varying freshwater discharge and an intrusion of salt water from the bay dependent upon the flow associated with the semi-diurnal component of the astronomical tide. A numerical model is applied to simulate the flow and salinity structures, which in the case of the Godavari Estuary have also been determined observationally and are documented in the literature. Observational data on the flow and salinity structure during two seasons are used in a comparison with theoretical results derived using a turbulent energy equation. Reasonable agreement is obtained between the model results and the observational data; in particular, streamlines are computed for the tidally averaged (or mean) component of the density-controlled flow.     

THE STUDY OF ADAPTABILITY OF Drepanopus bispinosus TO TEMPERATURE AND SALINITY IN THE ANTARCTIC BURTON LAKE

The tolerance to temperautre and salinity of a Calanoida copepod: Drepanopus bispinosus from the Burton Lake in the Vestfold Hills, Antarctica, was tested in each season. The results obtained show that the copepod has a marked physiological property of tolerance to low temperature and high salinity, and this property could be strengthened after winter. The response to different temperature and salinity of the copepod evidently expressed the tardy characteristics contrasted with seasons. This means that for a long term in early winter(lower temperature and higher salinity) the animal still has higher tolerance to lower salinity and higher temperature; and it is opposite in early summer. These physiological features are possibly caused by natural acclimatization in the lake. The experimental data were processed and plotted by computer. The correlation of animal's survival rate with the changes of temperature and salinity presented an approximately smooth surface of a three-degree elliptic sphere.     

Ion-Chromatographic Determination of Low Concentrations of Nitrate in Solutions of High Salinity

The determination of low concentrations of inorganic anions in water samples of high salinity is one of the most difficult tasks in analytical chemistry. There is, however, an increasing demand for the exact and reliable determination of nutrients even at very low concentration levels in environmental samples of complex composition. We therefore present the development, quality control and application of an easy and rugged method that makes possible the determination of trace amounts of nitrate in solutions with high concentrations of chloride (>30 000 mg L⁻¹) and a hundred-fold excess of bromide ions, based on ion chromatography with UV detection at λ = 210 nm. While chloride ions show no absorbance at this wavelength, a bromide concentration >1500 μg L⁻¹ severely interferes with nitrate determination at the trace level. On the contrary, at nitrate concentrations of >500 μg L⁻¹, this bromide interference becomes negligible. Consequently, to overcome the impact of bromide on the trace level determination of nitrate, all samples are spiked with a definite volume of a nitrate standard solution to obtain an overall nitrate concentration of >500 μg L⁻¹ which allows the exact and reliable determination of nitrate concentrations down to 25 μg L⁻¹. We will report the successful application of the method to samples of high salinity.