Raza Ahmad

Phytoremediation potential of Arundo donax in arsenic-contaminated synthetic wastewater

The present study reports the potential of Arundo donax for phytoextraction of arsenic from synthetic wastewater. A. donax plants were grown under greenhouse conditions in pots containing a nutrient solution amended with increasing doses of As (0, 50, 100, 300, 600 and 1000 microg L(-1)) for 21 days in a completely randomized design. Shoot and roots dry matter production, growth parameters, arsenic and nutrient tissue concentrations were measured at the end of the experiment. Increasing As concentration in nutrient solution caused an increase in shoot and root biomass without toxicity symptoms in A. donax growing under a range of As concentration from 50 to 600 microg L(-1). Elevated oxidative stress was observed at As supplied level of 1000 microg L(-1). The As doses up to 600 microg L(-1) did not affect the growth of A. donax. It is suggested that A. donax plants may be employed to treat contaminated waters containing arsenic concentrations up to 600 microg L(-1).

Simultaneous expression of choline oxidase, superoxide dismutase and ascorbate peroxidase in potato plant chloroplasts provides synergistically enhanced protection against various abiotic stresses.

Plants synthesize compatible solutes such as glycinebetaine (GB) in response to abiotic stresses. To evaluate the synergistic and protective effect of GB, transgenic potato plants expressing superoxide dismutase (SOD) and ascorbate peroxidase (APX) targeting to chloroplasts (referred to as SSA plants) were retransformed with a bacterial choline oxidase (codA) gene to synthesize GB in chloroplast in naturally occurring non-accumulator potato plants (including SSA) under the control of the stress-inducible SWPA2 promoter (referred to as SSAC plants). GB accumulation resulted in enhanced protection of these SSAC plants and lower levels of H(2)O(2) compared with SSA and non-transgenic (NT) plants after methyl viologen (MV)-mediated oxidative stress. Additionally, SSAC plants demonstrated synergistically enhanced tolerance to salt and drought stresses at the whole-plant level. GB accumulation in SSAC plants helped to maintain higher activities of SOD, APX and catalase following oxidative, salt and drought stress treatments than is observed in SSA and NT plants. Conclusively, GB accumulation in SSAC plants along with overexpression of antioxidant genes rendered the plants tolerant to multiple environmental stresses in a synergistic fashion.

Glycine betaine: a versatile compound with great potential for gene pyramiding to improve crop plant performance against environmental stresses

Plants are frequently exposed to a plethora of environmental stresses. Being sessile creatures, they have to tolerate any stresses by altering their metabolism. To achieve tolerance, plants synthesize compatible compounds such as glycine betaine (GB). Continuous research over the years has increased our understanding about the mechanisms of stress protection by GB, which range from an osmolyte to a chaperone and from maintenance of reactive oxygen species to gene expression inducer. Various crop plants have also been transformed to synthesize GB along with model plants by introducing bacterial or plant genes. The GB-synthesizing crop plants exhibit enhanced tolerance to various abiotic stresses and out-yield wild-type plants in stressful conditions. GB has also been utilized to improve enhanced stress tolerance by utilizing it in gene stacking experiments due to its synergistic and stabilizing effects. It is reviewed here (along with comparative analysis of GB synthesis pathways and its mechanism to improve tolerance) showing that gene stacking by using GB as one component provides substantial protection. This synergistic role of GB leads us to hypothesize that it can be utilized in virtually any kind of gene stacking experiments to develop crop plants to be grown in arable and marginal lands for better tolerance to ever-changing environmental conditions and to ensure food security in underdeveloped regions of the world.

Ascorbate and Glutathione: Protectors of Plants in Oxidative Stress

Reactive oxygen species (ROS) are produced naturally in plants during normal growth conditions. However, their production is accelerated manifold during various abiotic and biotic stresses. Rapid and efficient detoxification of ROS is vital to avoid any damage at cellular level. This is done by a well defined antioxidative system which comprises of various enzymes (superoxide dismutase, catalases and peroxidases) and low molecular weight compounds such as; praline, betaine, ascorbate and glutathione. Among these, ascorbate and glutathione are directly involved in scavenging of ROS. The present article will emphasize on the biosynthesis and role of ascorbate and glutathione during oxidative stress.

A newly isolated Pseudomonas sp. can degrade endosulfan via hydrolytic pathway

Endosulfan an organochlorinated pesticide was used extensively throughout the world. Its enormous and inadequate use creates environmental as well as health problems. A bacterial strain capable to utilize endosulfan as a sole source of sulfur was isolated from pesticide contaminated soil and identified as Pseudomonas sp. on the basis of 16S rRNA. Batch experiments were conducted at various initial concentrations of endosulfan, i.e. 5, 25, 50, 75 and 100 mg/l to study its rate of degradation. After three days of incubation, 70-80% of each initial concentration was degraded by the isolated strain as compared to the control. Degradation of endosulfan increased with the time of incubation and maximum degradation was observed after 5 days of incubation. GC-MS revealed that the major metabolite was endosulfan lactone, which accumulated after 5 days of incubation. Kinetic studies at various initial concentrations also revealed that the bacterium has very promising attitude to utilize endosulfan as sole source of sulfur. It was observed that the addition of auxiliary sulfur Fe(SO4)3 in any concentration (0.05, 0.01 and 0.1%) decreased the rate of degradation of endosulfan. The ratio of μmax/ Ks was high (0.03 mg/l) when endosulfan was single sulfur source as compared to the value recorded when Fe(SO4)3 was added alongwith the endosulfan. This indicates that the newly isolated bacterium attacks sulfur moiety for its degradation.