Elsayed Fathi Abd-Allah

Role of Trichoderma harzianum in mitigating NaCl stress in Indian mustard (Brassica juncea L) through antioxidative defense system

Salinity stress affected crop production of more than 20% of irrigated land globally. In the present study the effect of different concentrations of NaCl (0, 100, and 200 mM) on growth, physio-biochemical attributes, antioxidant enzymes, oil content, etc. in Brassica juncea and the protective role of Trichoderma harzianum (TH) was investigated. Salinity stress deteriorates growth, physio-biochemical attributes, that ultimately leads to decreased biomass yield in mustard seedlings. Higher concentration of NaCl (200 mM) decreased the plant height by 33.7%, root length by 29.7% and plant dry weight (DW) by 34.5%. On the other hand, supplementation of TH to NaCl treated mustard seedlings showed elevation by 13.8, 11.8, and 16.7% in shoot, root length and plant DW respectively as compared to plants treated with NaCl (200 mM) alone. Oil content was drastically affected by NaCl treatment; however, TH added plants showed enhanced oil percentage from 19.4 to 23.4% in the present study. NaCl also degenerate the pigment content and the maximum drop of 52.0% was recorded in Chl. ‘a’. Enhanced pigment content was observed by the application of TH to NaCl treated plants. Proline content showed increase by NaCl stress and maximum accumulation of 59.12% was recorded at 200 mM NaCl. Further enhancement to 70.37% in proline content was recorded by supplementation of TH. NaCl stress (200 mM) affirms the increase in H2O2 by 69.5% and MDA by 36.5%, but reduction in the accumulation is recorded by addition of TH to mustard seedlings. 200 mM NaCl elevated SOD, POD, APX, GR, GST, GPX, GSH, and GSSG in the present study. Further enhancement was observed by the application of TH to the NaCl fed seedlings. NaCl stress suppresses the uptake of important elements in both roots and shoots, however, addition of TH restored the elemental uptake in the present study. Mustard seedlings treated with NaCl and TH showed restricted Na uptake as compared to seedlings treated with NaCl alone. In conclusion, TH proved to be very beneficial in imparting resistance to the mustard plants against NaCl stress through improved uptake of essential elements, modulation of osmolytes and antioxidants.

Salinity Stress and Arbuscular Mycorrhizal Symbiosis in Plants

Soil salinity is one of the main abiotic stresses, which restrict the plant growth and development, and therefore causes major threat to crop productivity. To minimize the crop loss, plant biologists are searching alternatives to develop salt-tolerant crop plants through different means such as plant breeding and genetic engineering. These approaches are successful and presently under use in developed countries but are too costly for the developing countries. In the present scenarios, various methods are utilized all over the globe to mitigate the adverse effect of salinity. One of the commonly used methods is to use beneficial bacteria and fungi that colonize with the plant roots and ultimately alleviate the salinity stress in plants. Among them, application of arbuscular mycorrhizal (AM) fungi has been found to be very effective in mitigating the salinity stress and also improves the crop yield. Various parameters were thoroughly studied and reported in the literature and have demonstrated positive effect in plants subjected to AM fungi under different environmental stress including saline stress. This is attributed to increased antioxidative activities, osmolytes and osmoprotectants in tolerant plants. Deficiency of mineral content in plants under salt stress is compensated by the use of AM fungi as the hyphae of AM fungi acquire minerals in abundance and thereby prevent the plants against deleterious effects of salinity stress. Efficient use of AM fungi can bring the wonders in the field of agriculture with improved yield of crop under salt stress and soil health. Besides this, identification of novel genes that regulate and maintain the biosynthesis of proline and water status in plant cells will help plant researchers to utilize this beneficial interaction in more sustainable ways. The chapter will throw light on the use of AM fungal association in alleviating salt stress in plants and how to exploit this for improved productivity under growth-limited conditions.

Jasmonic Acid Modulates the Physio-Biochemical Attributes, Antioxidant Enzyme Activity, and Gene Expression in Glycine max under Nickel Toxicity

In present study, we evaluated the effects of Jasmonic acid (JA) on physio-biochemical attributes, antioxidant enzyme activity, and gene expression in soybean (Glycine max L.) plants subjected to nickel (Ni) stress. Ni stress decreases the shoot and root length and chlorophyll content by 37.23, 38.31, and 39.21%, respectively, over the control. However, application of JA was found to improve the chlorophyll content and length of shoot and root of Ni-fed seedlings. Plants supplemented with JA restores the chlorophyll fluorescence, which was disturbed by Ni stress. The present study demonstrated increase in proline, glycinebetaine, total protein, and total soluble sugar (TSS) by 33.09, 51.26, 22.58, and 49.15%, respectively, under Ni toxicity over the control. Addition of JA to Ni stressed plants further enhanced the above parameters. Ni stress increases hydrogen peroxide (H2O2) by 68.49%, lipid peroxidation (MDA) by 50.57% and NADPH oxidase by 50.92% over the control. Supplementation of JA minimizes the accumulation of H2O2, MDA, and NADPH oxidase, which helps in stabilization of biomolecules. The activities of superoxide dismutase (SOD), peroxidase (POD), catalase (CAT), and ascorbate peroxidase (APX) increases by 40.04, 28.22, 48.53, and 56.79%, respectively, over the control in Ni treated seedlings and further enhancement in the antioxidant activity was observed by the application of JA. Ni treated soybean seedlings showed increase in expression of Fe-SOD by 77.62, CAT by 15.25, POD by 58.33, and APX by 80.58% over the control. Nevertheless, application of JA further enhanced the expression of the above genes in the present study. Our results signified that Ni stress caused negative impacts on soybean seedlings, but, co-application of JA facilitate the seedlings to combat the detrimental effects of Ni through enhanced osmolytes, activity of antioxidant enzymes and gene expression.

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.

The Dynamic Changes of the Plasma Membrane Proteins and the Protective Roles of Nitric Oxide in Rice Subjected to Heavy Metal Cadmium Stress

The heavy metal cadmium is a common environmental contaminant in soils and has adverse effects on crop growth and development. The signaling processes in plants that initiate cellular responses to environmental stress have been shown to be located in the plasma membrane (PM). A better understanding of the PM proteome in response to environmental stress might provide new insights for improving stress-tolerant crops. Nitric oxide (NO) is reported to be involved in the plant response to cadmium (Cd) stress. To further investigate how NO modulates protein changes in the plasma membrane during Cd stress, a quantitative proteomics approach based on isobaric tags for relative and absolute quantification (iTRAQ) was used to identify differentially regulated proteins from the rice plasma membrane after Cd or Cd and NO treatment. Sixty-six differentially expressed proteins were identified, of which, many function as transporters, ATPases, kinases, metabolic enzymes, phosphatases, and phospholipases. Among these, the abundance of phospholipase D (PLD) was altered substantially after the treatment of Cd or Cd and NO. Transient expression of the PLD fused with green fluorescent peptide (GFP) in rice protoplasts showed that the Cd and NO treatment promoted the accumulation of PLD in the plasma membrane. Addition of NO also enhanced Cd-induced PLD activity and the accumulation of phosphatidic acid (PA) produced through PLD activity. Meanwhile, NO elevated the activities of antioxidant enzymes and caused the accumulation of glutathione, both which function to reduce Cd-induced H2O2 accumulation. Taken together, we suggest that NO signaling is associated with the accumulation of antioxidant enzymes, glutathione and PA which increases cadmium tolerance in rice via the antioxidant defense system.

Seed mycoflora ofLens esculenta and their biocontrol by chitosan

Thirty-two fungal species belonging to 17 genera were recorded on 45 seed samples of lentil (Lens esculenta) collected from different governorates in Egypt. The prevalent genera wereAlternaria, Aspergillus, Cladosporium, Fusarium andPenicillium. Chitosan enhanced suppression of seedborne mycoflora, as estimated using either agar plates or a blotter test of lentil seed samples. These results suggested an alternative non-toxic means for controlling seedborne fungi. Furthermore, pretreatment of lentil seeds with chitosan significantly reduced the natural contamination with mycotoxins — aflatoxins, ochratoxin A, citrinin and zearalenone — under storage conditions for 6 months.

Lipid metabolism in tomato and bean as a sensitive monitor for biocontrol of wilt diseases

The lipids metabolism of tomato and bean plants during biological control of wilt pathogens (Fusarium oxysporum f.sp.lycopersici andF. oxysporum f.sp.phaseoli, respectively) byBacillus subtilis was investigated. The interaction of wilt pathogens with both tomato and bean caused an imbalance and drastic reduction in total lipids, triacylglycerol, sterol and all phospholipd fractions except phosphatidic acid. The application of a formulated biocontrol agent,B. subtilis, eliminated the detrimental effect of both wilt pathogens and consequently prevented catabolism of lipid fractions in both tomato and bean. Moreover, the changes in the lipid fractions as a sensitive monitor for biocontrol of wilt diseases suggest a positive correlation between the application ofB. subtilis and improvement in the host metabolism towards anabolism.

Microbial cooperation in the rhizosphere improves liquorice growth under salt stress

ABSTRACT Liquorice (Glycyrrhiza uralensis Fisch.) is one of the most widely used plants in food production, and it can also be used as an herbal medicine or for reclamation of salt-affected soils. Under salt stress, inhibition of plant growth, nutrient acquisition and symbiotic interactions between the medicinal legume liquorice and rhizobia have been observed. We recently evaluated the interactions between rhizobia and root-colonizing Pseudomonas in liquorice grown in potting soil and observed increased plant biomass, nodule numbers and nitrogen content after combined inoculation compared to plants inoculated with Mesorhizobium alone. Several beneficial effects of microbes on plants have been reported; studies examining the interactions between symbiotic bacteria and root-colonizing Pseudomonas strains under natural saline soil conditions are important, especially in areas where a hindrance of nutrients and niches in the rhizosphere are high. Here, we summarize our recent observations regarding the combined application of rhizobia and Pseudomonas on the growth and nutrient uptake of liquorice as well as the salt stress tolerance mechanisms of liquorice by a mutualistic interaction with microbes. Our observations indicate that microbes living in the rhizosphere of liquorice can form a mutualistic association and coordinate their involvement in plant adaptations to stress tolerance. These results support the development of combined inoculants for improving plant growth and the symbiotic performance of legumes under hostile conditions.

Role of AM Fungi in Alleviating Drought Stress in Plants

Abiotic stress is increasing at an alarming rate throughout the globe. Drought stress is one of the major abiotic stresses responsible for hampering plant growth and development in many arid and semi-arid regions of the world. Drought stress disturbs the plant’s osmotic and ionic balance and hampers uptake of essential nutrients. Drought stress affects many physiological processes like gas exchange and water relations, pigments, organic solutes, lipid peroxidation, and electrolyte leakage, etc. Severe drought is also responsible for the generation of reactive oxygen species (ROS), which are deleterious to the normal functioning of the cell. However, plants are armed with certain antioxidants to defend themselves against these ROSs. Plants interact with certain microorganisms such as fungi that improve their performance during stress. Mycorrhizae is a close association between fungi and plant roots. Mycorrhizal association has shown to enhance crop growth, biomass, and mineral uptake under normal and drought conditions. This chapter throws light on the deleterious effects of drought stress and the beneficial effects of mycorrhizae in delaying or coping with toxic effects of drought stress and maintaining overall physiological balance.

Chapter 7 – Biological Control of Fungal Disease by Rhizobacteria under Saline Soil Conditions

Crop productivity is limited in arid and semiarid regions of the world due to adverse conditions such as drought and salt stresses. Drought and salinity are regarded as the major factors affecting plant diseases. The soil-borne pathogens may respond differently to salinity level. Some studies provided evidence for increased disease at increasing salinity. Biological control agents based on plant growth-promoting rhizobacteria (PGPR) are able to control plant diseases, increase plant growth, and provide resistance to environmental stresses, including drought and salt. Abiotic and biotic factors, such as salinity and drought, may influence the interactions between plant pathogens and biocontrol agents. This chapter provides a brief overview of our present knowledge about the biological control of plant disease by rhizobacteria and their modes of action under salt-stressed conditions.