Soil Chemical Analysis

Human health effects of air pollution

The aim of this review is to assess the mode of action and role of antioxidants as protection from heavy metal stress in roots, mycorrhizal fungi and mycorrhizae. Based on their chemical and physical properties three different molecular mechanisms of heavy metal toxicity can be distinguished: (a) production of reactive oxygen species by autoxidation and Fenton reaction; this reaction is typical for transition metals such as iron or copper, (b) blocking of essential functional groups in biomolecules, this reaction has mainly been reported for non-redox-reactive heavy metals such as cadmium and mercury, (c) displacement of essential metal ions from biomolecules; the latter reaction occurs with different kinds of heavy metals. Transition metals cause oxidative injury in plant tissue, but a literature survey did not provide evidence that this stress could be alleviated by increased levels of antioxidative systems. The reason may be that transition metals initiate hydroxyl radical production, which can not be controlled by antioxidants. Exposure of plants to non-redox reactive metals also resulted in oxidative stress as indicated by lipid peroxidation, H(2)O(2) accumulation, and an oxidative burst. Cadmium and some other metals caused a transient depletion of GSH and an inhibition of antioxidative enzymes, especially of glutathione reductase. Assessment of antioxidative capacities by metabolic modelling suggested that the reported diminution of antioxidants was sufficient to cause H(2)O(2) accumulation. The depletion of GSH is apparently a critical step in cadmium sensitivity since plants with improved capacities for GSH synthesis displayed higher Cd tolerance. Available data suggest that cadmium, when not detoxified rapidly enough, may trigger, via the disturbance of the redox control of the cell, a sequence of reactions leading to growth inhibition, stimulation of secondary metabolism, lignification, and finally cell death. This view is in contrast to the idea that cadmium results in unspecific necrosis. Plants in certain mycorrhizal associations are less sensitive to cadmium stress than non-mycorrhizal plants. Data about antioxidative systems in mycorrhizal fungi in pure culture and in symbiosis are scarce. The present results indicate that mycorrhization stimulated the phenolic defence system in the Paxillus-Pinus mycorrhizal symbiosis. Cadmium-induced changes in mycorrhizal roots were absent or smaller than those in non-mycorrhizal roots. These observations suggest that although changes in rhizospheric conditions were perceived by the root part of the symbiosis, the typical Cd-induced stress responses of phenolics were buffered. It is not known whether mycorrhization protected roots from Cd-induced injury by preventing access of cadmium to sensitive extra- or intracellular sites, or by excreted or intrinsic metal-chelators, or by other defence systems. It is possible that mycorrhizal fungi provide protection via GSH since higher concentrations of this thiol were found in pure cultures of the fungi than in bare roots. The development of stress-tolerant plant-mycorrhizal associations may be a promising new strategy for phytoremediation and soil amelioration measures.

Plant responses to abiotic stresses: heavy metal‐induced oxidative stress and protection by mycorrhization

Reactive oxygen species (ROS) were initially recognized as toxic by-products of aerobic metabolism. In recent years, it has become apparent that ROS plays an important signaling role in plants, controlling processes such as growth, development and especially response to biotic and abiotic environmental stimuli. The major members of the ROS family include free radicals like O2● −, OH● and non-radicals like H2O2 and 1O2. The ROS production in plants is mainly localized in the chloroplast, mitochondria and peroxisomes. There are secondary sites as well like the endoplasmic reticulum, cell membrane, cell wall and the apoplast. The role of the ROS family is that of a double edged sword; while they act as secondary messengers in various key physiological phenomena, they also induce oxidative damages under several environmental stress conditions like salinity, drought, cold, heavy metals, UV irradiation etc., when the delicate balance between ROS production and elimination, necessary for normal cellular homeostasis, is disturbed. The cellular damages are manifested in the form of degradation of biomolecules like pigments, proteins, lipids, carbohydrates and DNA, which ultimately amalgamate in plant cellular death. To ensure survival, plants have developed efficient antioxidant machinery having two arms, (i) enzymatic components like superoxide dismutase (SOD), catalase (CAT), ascorbate peroxidase (APX), guaiacol peroxidase (GPX), glutathione reductase (GR), monodehydroascorbate reductase (MDHAR) and dehydroascorbate reductase (DHAR); (ii) non-enzymatic antioxidants like ascorbic acid (AA), reduced glutathione (GSH), α-tocopherol, carotenoids, flavonoids and the osmolyte proline. These two components work hand in hand to scavenge ROS. In this review, we emphasize on the different types of ROS, their cellular production sites, their targets, and their scavenging mechanism mediated by both the branches of the antioxidant systems, highlighting the potential role of antioxidant

Reactive oxygen species (ROS) and response of antioxidants as ROS-scavengers during environmental stress in plants

Health risks of heavy metals in contaminated soils and food crops irrigated with wastewater in Beijing, China

Continually rising concentration of greenhouse gases (GHGs) in the atmosphere is increasing concerns over how to manage global warming. Quantification of sources and sinks of these gases have been carried out, but there remains incoherence among the estimates due to different nature of sources and processes related therewith. This renders inter-comparison and further utilization of available assessments quite incomparable. Except major point sources like thermal power plants, cement manufacturing, etc. which have been quantified confidently (Matthews et al., 2008), fugitive and sensitive sources/sinks still need proper quantification. Agriculture is one such system which plays dominating role in the global fluxes of CH4 and N2O, as their biggest emitter. Substantial inputs of energy, machinery, synthetic fertilizers and pesticides in the modern agriculture bear embodied emissions in addition to much focused direct emissions from soil (Lal, 2004a). At the same time, agricultural soils may reportedly act as considerable carbon sink (Lal, 2004b). Therefore it becomes essential to integrate all inputs-outputs to estimate the actual impact.

Carbon Footprints of Rice Cultivation under Different Tillage Practices in Rice-wheat System

Electrophoretic separation of humic acids obtained from soil was attempted through denaturing polyacrylamide gel electrophoresis (dn-PAGE) by modifying the known methods. The modifications of sample preparation and gel composition led to significant improvement in both visibility and intensity of humic acid profile. The comparative profile showed a similar nature of humic acid components in all the samples and the commercial standard. The Fourier transform infrared spectroscopy (FTIR) spectra indicated the presence of carboxyl and carbonyl functional groups and aliphatic chains in humic acid samples. The modified method facilitated better separation of humic acid. The results of the present study indicate the potential of dn-PAGE for electrophoretic separation of different components of humic acids.

Madhoolika Agrawal

Papers

Carbon Footprints of Rice Cultivation under Different Tillage Practices in Rice-wheat System

Electrophoretic Separation of Humic Acids Isolated from Tropical Soils Through Modified Denaturing Polyacrylamide Gel Electrophoresis

Evaluation of Tropospheric O3 Effects on Global Agriculture: A New Insight

Air pollution governance in China and India: Comparison and implications