Mohammad Abass Ahanger

Potassium induces positive changes in nitrogen metabolism and antioxidant system of oat (Avena sativa L cultivar Kent)

Potassium is actively involved in many functions such as enzyme activation, osmotic adjustment and uptake of deleterious ions like Na. Present report analyses the effectivity of different potassium salts on growth and certain components of nitrogen metabolism and antioxidant system in oat and their possible role in amelioration of water stress. Potassium induced enhancement in the activities of nitrate reductase and aminotransferases was evident indicating a positive role of potassium in nitrogen metabolism. Potassium supplementation enhanced activities of antioxidant enzymes (superoxide dismutase, catalase and ascorbate peroxidase) and contents of total phenols and tannins, probably strengthening both the enzymatic as well as non enzymatic antioxidant system. Free amino acids, proline and free sugars also exhibited the same trend in treated plants ensuring better plant growth.

Drought Tolerance: Role of Organic Osmolytes, Growth Regulators, and Mineral Nutrients

Plants are continuously exposed to various environmental stresses, which cause alteration in every physiological and biochemical pathway. Plants have evolved several mechanisms that allow a plant species to tolerate/combat stress. Greater synthesis and accumulation of compatible organic osmolytes and proper mineral nutrition help plants to bring osmoregulation so that the cell water content and turgor is maintained. Under stress conditions, synthesis and accumulation of several osmolytes like free sugars, amino compounds, such as proline and glycine betaine, sugar alcohols like mannitol, and other low molecular weight metabolites are increased. Macro mineral elements such as nitrogen, phosphorus, potassium, and calcium are required for normal growth and development of plants and are known to stimulate the synthesis of osmotically active solutes. Moreover, they are actively implicated in several physiological processes including enzyme activation, transport, photosynthesis, and protein synthesis. Various phytohormones are known to have defensive roles in plants exposed to environmental stresses and their synthesis and accumulation are upregulated on exposure to environmental stress. Present review throws light on the role of organic osmolytes, mineral nutrients, and also growth regulators especially abscisic acid, ethylene, and salicylic acid in increasing the plant tolerance to drought stress.

Chapter 3 – Arbuscular Mycorrhiza in Crop Improvement under Environmental Stress

Plants are continuously confronted by a variety of environmental stresses at various stages in their development. Extremely harse environmental conditions lead to oxidative stress because of the toxicities of certain ions and the overproduction of reactive oxygen species. Various stress-tolerance strategies are triggered that help plants to overcome/mitigate the stress-induced deleterious effects. These include morphological adaptations, osmoregulation, and enhanced activities of enzymatic as well as nonenzymatic antioxidants. To some extent, these strategies do help plants withstand unfavorable environmental conditions; however, in order to meet the food needs of the increasing world population, we have to develop/implement strategies to induce enhanced stress tolerance potential in crop plants. In connection with this, exploiting the biological means to induce enhanced stress tolerance for sustainable crop productivity is one of the promising means. Arbuscular mycorrhizal fungi (AMF) form symbiotic associations with the majority of the plants, altering root morphology and physiology as well. AMF-infected plants show efficient nutrient uptake and have higher enzymatic activities. The review in this chapter encompasses the general information about AMF and their possible role in stress mitigation.

Salinity stress induced alterations in antioxidant metabolism and nitrogen assimilation in wheat (Triticum aestivum L) as influenced by potassium supplementation

Experiments were conducted on two wheat (Triticum aestivum L) cultivars exposed to NaCl stress with and without potassium (K) supplementation. Salt stress induced using NaCl caused oxidative stress resulting into enhancement in lipid peroxidation and altered growth as well as yield. Added potassium led to significant improvement in growth having positive effects on the attributes including nitrogen and antioxidant metabolism. NaCl-induced stress triggered the antioxidant defence system nevertheless, the activity of antioxidant enzymes and the content of non-enzymatic antioxidants increased in K fed plants. Enhancement in the accumulation of osmolytes comprising free proline, sugars and amino acids was observed at both the developmental stages with K supplementation associated with improvement of the relative water content and ultimately yield. Potassium significantly increased uptake and assimilation of nitrogen with concomitant reduction in the Na ions and consequently Na/K ratio. Optimal K can be used as a potential tool for alleviating NaCl stress in wheat to some extent.

Plant responses to environmental stresses—from gene to biotechnology

Supplying food to an ever-increasing population is one of the biggest challenges worldwide. Environmental stresses make this situation even graver. New technological approaches are imperative. Recently, genetic engineering has contributed enormously to the development of genetically modified varieties of different crops such as cotton, maize, rice, canola and soybean. Identification of stress-responsive genes and their subsequent introgression or overexpression within sensitive crop species are now being widely carried out by plant scientists. In this review, the role of biotechnology in association with genomics and its successes, endeavours, prospects and challenges in developing stress-tolerant crop cultivars are discussed.

Mitigation of NaCl Stress by Arbuscular Mycorrhizal Fungi through the Modulation of Osmolytes, Antioxidants and Secondary Metabolites in Mustard (Brassica juncea L.) Plants

Present work was carried out to investigate the possible role of arbuscular mycorrhizal fungi (AMF) in mitigating salinity-induced alterations in Brassica juncea L. Exposure to NaCl stress altered the morphological, physio-biochemical attributes, antioxidant activity, secondary metabolites and phytohormones in the mustard seedlings. The growth and biomass yield, leaf water content, and total chlorophyll content were decreased with NaCl stress. However, AMF-inoculated plants exhibited enhanced shoot and root length, elevated relative water content, enhanced chlorophyll content, and ultimately biomass yield. Lipid peroxidation and proline content were increased by 54.53 and 63.47%, respectively with 200 mM NaCl concentration. Further increase in proline content and decrease in lipid peroxidation was observed in NaCl-treated plants inoculated with AMF. The antioxidants, superoxide dismutase, ascorbate peroxidase, glutathione reductase, and reduced glutathione were increased by 48.35, 54.86, 43.85, and 44.44%, respectively, with 200 mM NaCl concentration. Further increase in these antioxidants has been observed in AMF-colonized plants indicating the alleviating role of AMF to salinity stress through antioxidant modulation. The total phenol, flavonoids, and phytohormones increase with NaCl treatment. However, NaCl-treated plants colonized with AMF showed further increase in the above parameters except ABA, which was reduced with NaCl+AMF treatment over the plants treated with NaCl alone. Our results demonstrated that NaCl caused negative effect on B. juncea seedlings; however, colonization with AMF enhances the NaCl tolerance by reforming the physio-biochemical attributes, activities of antioxidant enzymes, and production of secondary metabolites and phytohormones.

Jasmonic acid alleviates negative impacts of cadmium stress by modifying osmolytes and antioxidants in faba bean (Vicia faba L.)

ABSTRACT We examined the role of jasmonic acid (JA) in faba bean under cadmium (Cd) stress, which reduces the growth, biomass yield, leaf relative water content (LRWC) and pigment systems. Hydrogen peroxide (H2O2) and lipid peroxidation (malondialdehyde [MDA]) levels increased by 2.78 and 2.24-fold, respectively, in plants under Cd stress, resulting in enhanced electrolyte leakage. Following foliar application to Cd-treated plants, JA restored growth, biomass yield, LRWC and pigment systems to appreciable levels and reduced levels of H2O2, MDA and electrolyte leakage. Proline and glycine betaine concentrations increased by 5.73 and 2.61-fold, respectively, in faba bean under Cd stress, with even higher concentrations observed following JA application to Cd-stressed plants. Superoxide dismutase, catalase, ascorbate peroxidase and glutathione reductase levels rose by 87.47%, 130.54%, 132.55% and 37.79%, respectively, with Cd toxicity, with further enhancement of antioxidant activities observed following foliar application of JA. Accumulation of Cd in roots, shoots and leaves was also minimized by external supplementation of JA. In conclusion, JA mitigates the negative impacts of Cd stress in faba bean plants by inhibiting the accumulation of Cd, H2O2 and MDA, and by enhancing osmolyte and antioxidant activities that reduce oxidative stress.

Jatropha curcas: An Overview

Jatropha curcas is a drought-resistant perennial tree attracting attention as biodiesel plant in the recent times, particularly because of its potential for growth in the regions of low rainfall. Present communication encompasses different aspects of Jatropha plantation and its uses including in soil conservation under stressful conditions. The paper also includes the reports about phytochemical constituents of Jatropha and also refers to less discussed aspects, i.e., possible allelopathic effects.

Alleviation of water and osmotic stress-induced changes in nitrogen metabolizing enzymes in Triticum aestivum L. cultivars by potassium

Present communication reports laboratory and pot experiments conducted to study the influence of water and osmotic stress on nitrogen uptake and metabolism in two wheat (Triticum aestivum L) cultivars with and without potassium supplementation. Polyethylene glycol 6000-induced osmotic stress/restricted irrigation caused a considerable decline in the activity of nitrate reductase, glutamate synthase, alanine and aspartate aminotransferases, and glutamate dehydrogenase. Potassium considerably improved nitrogen metabolism under normal water supply conditions and also resulted in amelioration of the negative impact of water and osmotic stresses indicating that potassium supplementation can be used as a potential tool for enhancing the nitrogen use efficiency in wheat for exploiting its genetic potential.

Zinc application mitigates the adverse effects of NaCl stress on mustard [Brassica juncea (L.) Czern & Coss] through modulating compatible organic solutes, antioxidant enzymes, and flavonoid content

ABSTRACT This study examined the protective effect of Zn on salt-stressed Brassica juncea plants using some key morphological and biochemical attributes at different developmental stages (30, 60, and 90 days after treatment [DAT]). Salt stress (200 mM) caused suppression in plant height, root length, and dry weight by 58.35%, 41.15%, and 53.33%, respectively, at 90 DAT, but Zn application improved these variables by 15.52%, 16.59%, and 11.45%, respectively. Furthermore, 200 mM NaCl decreased total chlorophyll by 45.32% and relative water content by 27.62% at 90 DAT, whereas Zn application compensated the decrease in the levels of both variables. NaCl (200 mM) increased H2O2, malondialdehyde, and electrolyte leakage by 70.48%, 35.25%, and 68.39%, respectively, at 90 DAT, but Zn supplementation appreciably reduced these variables. Except for catalase, enzymatic antioxidant activity increased under NaCl stress. Zn application with salt further increased the activities of superoxide dismutase, catalase, ascorbate peroxidase, glutathione reductase, and glutathione-S-transferase by 33.51%, 9.21%, 10.98%, 17.46%, and 12.87%, respectively, at 90 DAT. At 90 DAT, salt stress increased flavonoids by 24.88%, and Zn supply by a further 7.68%. Overall, Zn mitigated the adverse effects of salt stress through osmotic adjustment, as well as by modulating the oxidative defense system and flavonoid contents.