Abdulaziz A. Alqarawi

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.

Alleviation of salt-induced adverse impact via mycorrhizal fungi in Ephedra aphylla Forssk

The current investigation was carried out to examine the role of arbuscular mycorrhizal fungi (AMF) in alleviating adverse effects of salt stress in Ephedra aphylla. The plants were exposed to 75 and 150 mM sodium chloride (NaCl) stress with and without application of AMF. Salt stress caused significant decrease in chlorophyll and carotenoid contents; however, the application of AMF restored the pigments content in salt-affected plants. Proline, phenols, and lipid peroxidation were increased with increasing concentration of NaCl, but lower accumulation has been reported in plants treated with AMF. NaCl stress also showed increase in different antioxidant enzymes activities (catalase, ascorbate peroxidase, peroxidase, glutathione reductase, and superoxide dismutase), and further increase was observed in plants treated with AMF. The nutrient uptake, Na+ and Na/K ratio increased and potassium and phosphorus were decreased with increasing concentration of NaCl in the present study. However, the colonization with AMF significantly increased K+ and P and reduced Na+ uptake. It is concluded that presown soil treatment with AMF reduced severity of salt stress in E. aphylla through alterations in physiological parameters, antioxidants and uptake of nutrients.

The Interaction between Arbuscular Mycorrhizal Fungi and Endophytic Bacteria Enhances Plant Growth of Acacia gerrardii under Salt Stress.

Microbes living symbiotically in plant tissues mutually cooperate with each other by providing nutrients for proliferation of the partner organism and have a beneficial effect on plant growth. However, few studies thus far have examined the interactive effect of endophytic bacteria and arbuscular mycorrhizal fungi (AMF) in hostile conditions and their potential to improve plant stress tolerance. In this study, we investigated how the synergistic interactions of endophytic bacteria and AMF affect plant growth, nodulation, nutrient acquisition and stress tolerance of Acacia gerrardii under salt stress. Plant growth varied between the treatments with both single inoculants and was higher in plants inoculated with the endophytic B. subtilis strain than with AMF. Co-inoculated A. gerrardii had a significantly greater shoot and root dry weight, nodule number, and leghemoglobin content than those inoculated with AMF or B. subtilis alone under salt stress. The endophytic B. subtilis could alleviate the adverse effect of salt on AMF colonization. The differences in nitrate and nitrite reductase and nitrogenase activities between uninoculated plants and those inoculated with AMF and B. subtilis together under stress were significant. Both inoculation treatments, either B. subtilis alone or combined with AMF, enhanced the N, P, K, Mg, and Ca contents and phosphatase activities in salt-stressed A. gerrardii tissues and reduced Na and Cl concentration, thereby protecting salt-stressed plants from ionic and osmotic stress-induced changes. In conclusion, our results indicate that endophytic bacteria and AMF contribute to a tripartite mutualistic symbiosis in A. gerrardii and are coordinately involved in the plant adaptation to salt stress tolerance.

Alleviation of cadmium stress in Solanum lycopersicum L. by arbuscular mycorrhizal fungi via induction of acquired systemic tolerance.

Experiments were conducted to evaluate cadmium (Cd) stress-induced changes in growth, antioxidants and lipid composition of Solanum lycopersicum with and without arbuscular mycorrhizal fungi (AMF). Cadmium stress (50 μM) caused significant changes in the growth and physio-biochemical attributes studied. AMF mitigated the deleterious impact of Cd on the parameters studied. Cadmium stress increased malonaldehyde and hydrogen peroxide production but AMF reduced these parameters by mitigating oxidative stress. The activity of antioxidant enzymes enhanced under Cd treatment and AMF inoculation further enhanced their activity, thus strengthening the plant’s defense system. Proline and phenol content increased in Cd-treated as well as AMF-inoculated plants providing efficient protection against Cd stress. Cadmium treatment resulted in great alterations in the main lipid classes leading to a marked change in their composition. Cadmium stress caused a significant reduction in polyunsaturated fatty acids resulting in enhanced membrane leakage. The present study supports the use of AMF as a biological means to ameliorate Cd stress-induced changes in tomato.

Alleviation of abiotic salt stress in Ochradenus baccatus (Del.) by Trichoderma hamatum (Bonord.) Bainier

The current study was taken up to examine the role of bioagent (Trichoderma hamatum) in mitigating the deleterious effects of NaCl stress in Ochradenus baccatus. Varying concentrations of salt (0, 75, and 150 mM) were used to observe the effect on growth, pigments, some key metabolic attributes, antioxidant enzymes, and elemental accumulation in O. baccatus. The results indicated significant decrease in seed germination, plant growth, pigment content, membrane stability index, tissue water content, and total lipid content with salt stress. Lipid peroxidation increases with the increasing concentration of NaCl. Moreover, salinity stimulated the biosynthesis of phenols, diacylglycerol, sterol esters, nonesterified fatty acids, and enzymatic antioxidants like superoxide dismutase, catalase, peroxidase, ascorbate peroxidase, glutathione reductase. The Na+ content in shoot increases with elevated levels of NaCl concentration, accompanied with significant decreases in K+, Mg2+, and Ca2+. Application of bioagent (T. hamatum) has been observed to alleviate the antagonistic effect of salt stress on plant growth and metabolic processes. In absence and presence of salt stress, the bioagent stimulated the plant growth and alter the plant metabolism through the modification of the above parameters.

Enhancing growth performance and systemic acquired resistance of medicinal plant Sesbania sesban (L.) Merr using arbuscular mycorrhizal fungi under salt stress

Pot experiments were conducted to evaluate the damaging effects of salinity on Sesbania sesban plants in the presence and absence of arbuscular mycorrhizal fungi (AMF). The selected morphological, physiological and biochemical parameters of S. sesban were measured. Salinity reduced growth and chlorophyll content drastically while as AMF inoculated plants improved growth. A decrease in the number of nodules, nodule weight and nitrogenase activity was also evident due to salinity stress causing reduction in nitrogen fixation and assimilation potential. AMF inoculation increased these parameters and also ameliorated the salinity stress to some extent. Antioxidant enzymes like superoxide dismutase (SOD), catalase (CAT), ascorbate peroxidase (APX) and glutathione reductase (GR) as well as non enzymatic antioxidants (ascorbic acid and glutathione) also exhibited great variation with salinity treatment. Salinity caused great alterations in the endogenous levels of growth hormones with abscisic acid showing increment. AMF inoculated plants maintained higher levels of growth hormones and also allayed the negative impact of salinity.

Effect of salinity on moisture content, pigment system, and lipid composition in Ephedra alata Decne

The present work was carried out to uncover the effect of salinity stress on shoot moisture percentage, pigment content and lipid composition of Ephedra alata Decne. The results suggested that salinity caused significant decrease in plant moisture content. The chl. a, b and carotenoids showed significant decrease with increasing concentration of salt. Total pigment content also showed decline at all salt stress levels. Salt stress caused significant decrease in total lipids (TL), triacylglycerol (TG) and sterol (S) accompanied with an increase in diacylglycerol (DG), sterol ester (SE), and non-esterified fatty acids (FAA) of E. alata. Moreover, saline stress caused significant decrease in all phospholipid fractions except phosphatidic acid which increases during salt stress. Salinity stress resulted in increase of saturated fatty acids and decreases the percentage of un-saturated fatty acids in E. alalta.

Arbuscular mycorrhizal fungi enhances salinity tolerance of Panicum turgidum Forssk by altering photosynthetic and antioxidant pathways

Present experiments were conducted to assess the response of Panicum turgidum to salinity and possible role of arbuscular mycorrhizal fungi (AMF) in enhancing the salt tolerance. The activities of antioxidant enzymes such as superoxide dismutase (SOD), catalase (CAT), peroxidase (POD), glutathione reductase (GR) and compatible solutes were increased by salt stress and were further enhanced by AMF inoculation. Hydrogen peroxide and malonaldehyde content increased in salt-stressed plants while a reduction was observed due to AMF inoculation. Salt-stressed plants showed higher activities of pyruvate orthophosphate dikinase (PPDK), phosphoenolpyruvate carboxylase (PEPC) and malate dehydrogenase as compared to control and AMF-inoculated plants. Salt stress caused significant decrease in phosphorous, potassium and calcium uptake but an increase in sodium uptake was observed. AMF alleviate salinity-induced negative impact on the plant growth and nutrient uptake by reducing the oxidative damage through strengthening of the antioxidant system.

Bioremediation of adverse impact of cadmium toxicity on Cassia italica Mill by arbuscular mycorrhizal fungi.

Cassia italica Mill is an important medicinal plant within the family Fabaceae. Pot experiment was conducted to evaluate cadmium stress induced changes in physiological and biochemical attributes in C. italica with and without arbuscular mycorrhizal fungi (AMF). Cadmium stressed plant showed reduced chlorophyll pigment and protein content while AMF inoculation enhanced the chlorophyll and protein content considerably. AMF also ameliorated the cadmium stress induced reduction in total chlorophyll and protein contents by 19.30% and 38.29%, respectively. Cadmium stress enhanced lipid peroxidation while AMF inoculation reduced lipid peroxidation considerably. Increase in proline and phenol content was observed due to cadmium stress and AMF inoculation caused a further increase in proline and phenol content ensuring better growth under stressed conditions. AMF alone also enhanced proline and phenol content. Activity of antioxidant enzymes enhanced under cadmium treatment and AMF inoculation further enhanced their activity thereby strengthening the antioxidant system. Enhanced activities of antioxidants and increased accumulation of osmolytes help plants to avoid damaging impact of oxidative damage. The research has shown that AMF inoculation mitigated the negative impact of stress by reducing the lipid peroxidation and enhancing the antioxidant activity. The present study strongly supports employing AMF as the biological mean for enhancing the cadmium stress tolerance of C. italica.

Arbuscular mycorrhizal symbiosis and abiotic stress in plants: A review

Abiotic stresses (such as salinity, drought, cold, heat, mineral deficiency and metals/metalloids) have become major threats to the global agricultural production. These stresses in isolation and/or combination control plant growth, development and productivity by causing physiological disorders, ion toxicity, and hormonal and nutritional imbalances. Some soil microorganisms like arbuscular mycorhizal fungi (AMF) inhabit the rhizosphere and develop a symbiotic relationship with the roots of most plant species. AMF can significantly improve resistance of host plants to varied biotic and abiotic stresses. Taking into account recent literature, this paper: (a) overviews major abiotic stresses and introduces the arbuscular mycorrhizae symbiosis (b) appraises the role and underlying major mechanisms of AMF in plant tolerance to major abiotic stresses including salinity, drought, temperature regimes (cold and heat), nutrient-deficiency, and metal/metalloids; (c) discusses major molecular mechanisms potentially involved in AMF-mediated plant-abiotic stress tolerance; and finally (d) highlights major aspects for future work in the current direction.