Arbuscular mycorrhizal fungi reduce soil N2O emissions by altering root traits and soil denitrifier community composition.

Arbuscular mycorrhizal fungi (AMF) increase the ability of plants to obtain nitrogen (N) from the soil, and thus can affect emissions of nitrous oxide (N2O), a long-lived potent greenhouse gas. However, the mechanisms underlying the effects of AMF on N2O emissions are still poorly understood, particularly in agroecosystems with different forms of N fertilizer inputs. Utilizing a mesocosm experiment in field, we examined the effects of AMF on N2O emissions via their influence on maize root traits and denitrifying microorganisms under ammonia and nitrate fertilizer input using 15N isotope tracer. Here we show that the presence of AMF alone or both maize roots and AMF increased maize biomass and their 15N uptake, root length, root surface area, and root volume, but led to a reduction in N2O emissions under both N input forms. Random forest model showed that root length and surface area were the most important predictors of N2O emissions. Additionally, the presence of AMF reduced the (nirK + nirS)/nosZ ratio by increasing the relative abundance of nirS-Bradyrhizobium and Rubrivivax with ammonia input, but reducing nosZ-Azospirillum, Cupriavidus and Rhodopseudomonas under both fertilizer input. Further, N2O emissions were significantly and positively correlated with the nosZ-type Azospirillum, Cupriavidus and Rhodopseudomonas, but negatively correlated with the nirS-type Bradyrhizobium and Rubrivivax. These results indicate that AMF reduce N2O emissions by increasing root length to explore N nutrients and altering the community composition of denitrifiers, suggesting that effective management of N fertilizer forms interacting with the rhizosphere microbiome may help mitigate N2O emissions under future N input scenarios.

Optimization of phytase production by Penicillium oxalicum in solid-state fermentation for potential as a feed additive.

The study aims to statistically optimize the phytase production by Penicillium oxalicum PBG30 in solid-state fermentation using wheat bran as substrate. Variables viz. pH, incubation days, MgSO4, and Tween-80 were the significant parameters identified through the Plackett-Burman design (PBD) that majorly influenced the phytase production. Further, central composite design (CCD) method of response surface methodology (RSM) defined the optimum values for these factors i.e., pH 7.0, 5 days of incubation, 0.75% of MgSO4, and 3.5% of Tween-80 that leads to maximum phytase production of 475.42 U/g DMR. Phytase production was also sustainable in flasks and trays of different sizes with phytase levels ranging from 394.95 to 475.42 U/g DMR. Enhancement in phytase production is 5.6-fold as compared to unoptimized conditions. The in-vitro dephytinization of feed showed an amelioration in the nutritive value by releasing inorganic phosphate and other nutrients in a time-dependent manner. The highest amount of inorganic phosphate (33.986 mg/g feed), reducing sugar (134.4 mg/g feed), and soluble protein (115.52 mg/g feed) was achieved at 37 °C with 200 U of phytase in 0.5 g feed for 48 h. This study reports the economical and large-scale production of phytase with applicability in enhancing feed nutrition.

Arbuscular mycorrhiza induces low oxidative burst in drought-stressed walnut through activating antioxidant defense systems and heat shock transcription factor expression.

Arbuscular mycorrhizal fungi (AMF) have important roles in enhancing drought tolerance of host plants, but it is not clear whether and how AMF increase drought tolerance in walnut (Juglans regia). We hypothesized that AMF could activate antioxidant defense systems and heat shock transcription factors (Hsfs) transcription levels to alleviate oxidative damage caused by drought. The walnut variety 'Liaohe No. 1' was inoculated with Diversispora spurca and exposed to well-watered (WW, 75% of the maximum soil water capacity) and drought stress (DS, 50% of the maximum soil water capacity) for 6 weeks. Plant growth, antioxidant defense systems, and expressions of five JrHsfs in leaves were studied. Such drought treatment inhibited root mycorrhizal colonization, while plant growth performance was still improved by AMF inoculation. Mycorrhizal fungal inoculation triggered the increase in soluble protein, glutathione (GSH), ascorbic acid (ASC), and total ASC contents and ascorbic peroxidase and glutathione reductase activities, along with lower hydrogen peroxide (H2O2), superoxide anion radical (O2 •-), and malondialdehyde (MDA) levels, compared with non-inoculation under drought. Mycorrhizal plants also recorded higher peroxidase, catalase, and superoxide dismutase activities than non-mycorrhizal plants under drought. The expression of JrHsf03, JrHsf05, JrHsf20, JrHsf22, and JrHsf24 was up-regulated under WW by AMF, while the expression of JrHsf03, JrHsf22, and JrHsf24 were up-regulated only under drought by AMF. It is concluded that D. spurca induced low oxidative burst in drought-stressed walnut through activating antioxidant defense systems and part Hsfs expressions.

Insights into the molecular aspects of salt stress tolerance in mycorrhizal plants.

Salt stress is one of the major abiotic stresses that severely affect plant growth and yield, and also affect the livelihood of people all around the world. Arbuscular mycorrhizal fungi (AMF) colonize majority of terrestrial plants, including halophytes, xerophytes and glycophytes, and facilitate their functioning by various physiological, biochemical and molecular processes. In the past two decades, significant progress has been made to understand the role of AMF in mitigating salt stress and improving plant growth and productivity under saline conditions. Several studies focusing on the biochemical and physiological mechanisms that mycorrhizal plants employ to combat salt stress have been carried out. This review reinforces such studies and gives further insights into the molecular aspects of tolerance to salt stress in the plants colonized by AMF. It emphasises on the role of AMF in sensing and signalling salt stress, expression of aquaporin-encoding genes, Na+/H+ antiporters and transporters involved in Na+ exclusion, CNGCs and late embryogenesis abundant proteins in relation to salt stress tolerance. Further, this paper also reviews the accrual of compatible osmolytes, phytohormones and nitric oxide for understanding the benefits of this symbiosis under saline environment, and provides a benchmark information to understand the contribution of mycorrhizal symbiosis at molecular level and will attract attention of researchers to develop and highlight the future research programs in this field.

Effect of Rhizoglomus fasciculatum and Paecilomyces lilacinus in the biocontrol of root-knot nematode, Meloidogyne incognita in Capsicum annuum L.

Root-knot nematodes possess a major threat to agricultural production of various crops worldwide. The intensive use of chemical nematicides to control plant parasitic nematodes has adverse effects on our environment and human health. Owing to the importance of developing new strategies, an experiment was conducted to reveal the influence of arbuscular mycorrhizal fungus, Rhizoglomus fasciculatum and nematophagous fungus, Paecilomyces lilacinus alone or in combination with various organic amendments such as superphosphate, green and organic manure to control the infection of root-knot, nematode Meloidogyne incognita in a vegetable crop Capsicum annuum. These two fungi along with soil amendments significantly improved plant growth and fruit yield and effectively controlled infection of M. incognita. The dual inoculation of P. lilacinus and R. fasciculatum reduced the number of galls and egg masses, thereby revealing the controlled proliferation of M. incognita infection in C. annuum roots. The beneficial effect of these fungi further increased on supplementation of soil with organic or green manures. Inoculation of C. annuum with these two fungi showed a significant increase in egg parasitization; however, maximum effect was detected on dual inoculation. Amongst the soil amendments, the best response was obtained in case of green manure along with mycorrhizal fungus and P. lilacinus. Present study revealed that nematophagous and AM fungi, in combination with green manure were effective in controlling M. incognita, thus suggesting the use of such agents for biocontrol of plant parasitic nematodes in agriculture.

The Change in Fatty Acids and Sugars Reveals the Association between Trifoliate Orange and Endophytic Fungi.

Endophytes have the ability to improve plant nutrition alongside their agronomic performance, among which arbuscular mycorrhizal fungi provide the most benefits to their host. Previously, we reported for the first time that an arbuscular mycorrhizal-like fungus Piriformospora indica had the ability to colonize roots of trifoliate orange (Poncirus trifoliata) and conferred positive effects on nutrient acquisition. Present study showed the changes in fatty acids and sugars to unravel the physiological and symbiotic association of trifoliate orange with P. indica and an arbuscular mycorrhizal fungus, Funneliformis mosseae singly or in combination. All the endophytic fungi collectively increased fructose, glucose, and sucrose content in leaves and roots, along with a relatively higher increase with P. indica inoculation than with F. mosseae alone or dual inoculation. Treatment with P. indica increased the concentration of part unsaturated fatty acids such as C18:3N6, C20:2, C20:3N6, C20:4N6, C20:3N3, C20:5N3, C22:1N9, and C24:1. Additionally, P. indica induced the increase in the concentration of part saturated fatty acids such as C6:0, C8:0, C13:0, C14:0, and C24:0. F. mosseae hardly changed the content of fatty acids, except for increase in C14:0 and C20:5N3. Double inoculation only reduced the C21:0, C10:0, C12:0, C18:3N3, and C18:1 content and increased the C20:5N3 content. These endophytic fungi up-regulated the root PtFAD2, PtFAD6, PtΔ9, and PtΔ15 gene expression level, coupled with a higher expression of PtFAD2 and PtΔ9 by P. indica than by F. mosseae. It was concluded that P. indica exhibited a stronger response, for sugars and fatty acids, than F. mosseae on trifoliate orange. Such results also reveal the Pi (an in vitro culturable fungus) as a bio-stimulator applying to citriculture.

Mycorrhizal symbiosis down-regulates or does not change root aquaporin expression in trifoliate orange under drought stress.

Arbuscular mycorrhizas absorb water from soil to host plants, while the relationship between mycorrhizas and aquaporins (AQPs, membrane water channel proteins, which function in water transport) in mycorrhizal plants is unclear. In this study, Funneliformis mosseae-colonized trifoliate orange (Poncirus trifoliata) seedlings were grown in pots fitted with 37-µm nylon meshes at the bottom of each pot to allow mycorrhizal hyphae absorb water from an outer beaker. The expression of seven plasma membrane intrinsic proteins (PIPs) genes, six tonoplast intrinsic proteins (TIPs) genes, and four nodulin-26 like intrinsic proteins (NIPs) genes were analyzed in roots of both well-watered (WW) and drought stressed (DS) plants. The six-week DS plants dramatically increased hyphal water absorption rate by 1.4 times, as compared with WW plants. Mycorrhizal plants exhibited greater plant growth performance, leaf water status (water potential and relative water content), and gas exchange under both WW and DS conditions. Mycorrhizal inoculation induced diverse expression patterns in these AQPs under WW: up-regulation of PtNIP1;1, PtPIP2;1, and PtPIP2;5, down-regulation of PtNIP1;2, PtNIP6;1, PtPIP1;2, PtPIP1;5, PtPIP2;8, PtTIP1;1, PtTIP1;2, PtTIP1;3, and PtTIP5;1, and no changes in other AQPs. However, the expression of PtPIPs and PtNIPs was down-regulated by mycorrhizal inoculation under DS, and PtTIPs was not induced by mycorrhizal colonization under DS. The expression pattern of AQPs in response to mycorrhizas under DS is a way of mycorrhizal plants to minimize water loss.

Ultrastructural evidence for AMF mediated salt stress mitigation in Trigonella foenum-graecum.

The study unveils that inoculation with arbuscular mycorrhizal fungus (Glomus intraradices Schenck and Smith) prevents salt-induced ultrastructural alterations in fenugreek (Trigonella foenum-graecum L.) plants. Mycorrhizal (M) and non-mycorrhizal (NM) fenugreek plants were subjected to four levels of NaCl (0, 50, 100, and 200 mM NaCl). Salt-induced ultrastructural changes were captured using a Transmission Electron Microscope. Effects of salt on the ultrastructure of cells include shrinkage of protoplasm, widening apoplastic space between cell wall and cell membrane, disorganization of grana in chloroplast--swelling and reduction in the number of thylakoids, disintegration of chloroplast membrane, accumulation of plastoglobules, dilation of cristae and denser matrix in mitochondria, and aggregation of chromatin in nucleus. However, the extent of salt-induced ultrastructural damage was less in M plants as compared to NM plants. Lower lipid peroxidation and electrolyte leakage in M plants also indicated less membrane damage. This reduction of ultrastructure damage is a demonstration of enhanced tolerance in M plants to salt stress. The AMF-mediated lesser damage may be due to higher osmolyte (glycinebetaine, sugars) and polyamines concentration, and more and bigger plastoglobules (higher α-tocopherol concentration) in M plants as compared to NM plants. While lower Na(+) and Cl(-) ions assures less ionic toxicity, higher osmolytes and tocopherols ensure osmotic adjustment and better capacity to scavenge free radicals generated due to salt stress, respectively.

Contribution of Glomus intraradices inoculation to nutrient acquisition and mitigation of ionic imbalance in NaCl-stressed Trigonella foenum-graecum.

The study aimed to investigate the effects of an AM fungus (Glomus intraradices Schenck and Smith) on mineral acquisition in fenugreek (Trigonella foenum-graecum) plants under different levels of salinity. Mycorrhizal (M) and non-mycorrhizal (NM) fenugreek plants were subjected to four levels of NaCl salinity (0, 50, 100, and 200 mM NaCl). Plant tissues were analyzed for different mineral nutrients. Leaf senescence (chlorophyll concentration and membrane permeability) and lipid peroxidation were also assessed. Under salt stress, M plants showed better growth, lower leaf senescence, and decreased lipid peroxidation as compared to NM plants. Salt stress adversely affected root nodulation and uptake of NPK. This effect was attenuated in mycorrhizal plants. Presence of the AM fungus prevented excess uptake of Na(+) with increase in NaCl in the soil. It also imparted a regulatory effect on the translocation of Na(+) ions to shoots thereby maintaining lower Na(+) shoot:root ratios as compared to NM plants. Mycorrhizal colonization helped the host plant to overcome Na(+)-induced Ca(2+) and K(+) deficiencies. M plants maintained favorable K(+):Na(+), Ca(2+):Na(+), and Ca(2+):Mg(2+) ratios in their tissues. Concentrations of Cu, Fe, and Zn(2+) decreased with increase in intensity of salinity stress. However, at each NaCl level, M plants had higher concentration of Cu, Fe, Mn(2+), and Zn(2+) as compared to NM plants. M plants showed reduced electrolyte leakage in leaves as compared to NM plants. The study suggests that AM fungi contribute to alleviation of salt stress by mitigation of NaCl-induced ionic imbalance thus maintaining a favorable nutrient profile and integrity of the plasma membrane.

Arbuscular mycorrhizal fungi in alleviation of salt stress: a review.

BACKGROUND: Salt stress has become a major threat to plant growth and productivity. Arbuscular mycorrhizal fungi colonize plant root systems and modulate plant growth in various ways. SCOPE: This review addresses the significance of arbuscular mycorrhiza in alleviation of salt stress and their beneficial effects on plant growth and productivity. It also focuses on recent progress in unravelling biochemical, physiological and molecular mechanisms in mycorrhizal plants to alleviate salt stress. CONCLUSIONS: The role of arbuscular mycorrhizal fungi in alleviating salt stress is well documented. This paper reviews the mechanisms arbuscular mycorrhizal fungi employ to enhance the salt tolerance of host plants such as enhanced nutrient acquisition (P, N, Mg and Ca), maintenance of the K(+) : Na(+) ratio, biochemical changes (accumulation of proline, betaines, polyamines, carbohydrates and antioxidants), physiological changes (photosynthetic efficiency, relative permeability, water status, abscissic acid accumulation, nodulation and nitrogen fixation), molecular changes (the expression of genes: PIP, Na(+)/H(+) antiporters, Lsnced, Lslea and LsP5CS) and ultra-structural changes. Theis review identifies certain lesser explored areas such as molecular and ultra-structural changes where further research is needed for better understanding of symbiosis with reference to salt stress for optimum usage of this technology in the field on a large scale. This review paper gives useful benchmark information for the development and prioritization of future research programmes.

Improved tolerance of Acacia nilotica to salt stress by Arbuscular mycorrhiza, Glomus fasciculatum may be partly related to elevated K/Na ratios in root and shoot tissues.

A pot experiment was conducted to examine the effect of arbuscular mycorrhizal fungus, Glomus fasciculatum, and salinity on the growth of Acacia nilotica. Plants were grown in soil under different salinity levels (1.2, 4.0, 6.5, and 9.5 dS m(-1)). In saline soil, mycorrhizal colonization was higher at 1.2, 4.0, and 6.5 dS m(-1) salinity levels in AM-inoculated plants, which decreased as salinity levels further increased (9.5 dS m(-1)). Mycorrhizal plants maintained greater root and shoot biomass at all salinity levels compared to nonmycorrhizal plants. AM-inoculated plants had higher P, Zn, and Cu concentrations than uninoculated plants. In mycorrhizal plants, nutrient concentrations decreased with the increasing levels of salinity, but were higher than those of the nonmycorrhizal plants. Mycorrhizal plants had greater Na concentration at low salinity levels (1.2, 4.0 dS m(-1)), which lowered as salinity levels increased (6.5, 9.5 dS m(-1)), whereas Na concentration increased in control plants. Mycorrhizal plants accumulated a higher concentration of K at all salinity levels. Unlike Na, the uptake of K increased in shoot tissues of mycorrhizal plants with the increasing levels of salinity. Our results indicate that mycorrhizal fungus alleviates deleterious effects of saline soils on plant growth that could be primarily related to improved P nutrition. The improved K/Na ratios in root and shoot tissues of mycorrhizal plants may help in protecting disruption of K-mediated enzymatic processes under salt stress conditions.

Improved growth and essential oil yield and quality in Foeniculum vulgare mill on mycorrhizal inoculation supplemented with P-fertilizer.

Two arbuscular mycorrhizal (AM) fungi Glomus macrocarpum and Glomus fasciculatum significantly improved growth and essential oil concentration of Foeniculum vulgare Mill. However, AM inoculation of plants along with phosphorus fertilization significantly enhanced growth, P-uptake and essential oil content of plants compared to either of the components applied separately. Among the two fungal inoculants, G. fasciculatum registered the highest growth at both levels of phosphorus used with up to 78% increase in essential oil concentration of fennel seeds over non-mycorrhizal control. The essential oil characterization by gas liquid chromatography revealed that the level of anethol was significantly enhanced on mycorrhization.

Mycorrhizal inoculant alleviates salt stress in Sesbania aegyptiaca and Sesbania grandiflora under field conditions: evidence for reduced sodium and improved magnesium uptake.

A field experiment was conducted to examine the effect of the arbuscular mycorrhizal fungus Glomus macrocarpum and salinity on growth of Sesbania aegyptiaca and S. grandiflora. In the salt-stressed soil, mycorrhizal root colonisation and sporulation was significantly higher in AM-inoculated than in uninoculated plants. Mycorrhizal seedlings had significantly higher root and shoot dry biomass production than non-mycorrhizal seedlings grown in saline soil. The content of chlorophyll was greater in the leaves of mycorrhiza-inoculated as compared to uninoculated seedlings. The number of nodules was significantly higher in mycorrhizal than non-mycorrhizal plants. Mycorrhizal seedling tissue had significantly increased concentrations of P, N and Mg but lower Na concentration than non-mycorrhizal seedlings. Under salinity stress conditions both Sesbania sp. showed a high degree of dependence on mycorrhizae, increasing with the age of the plants. The reduction in Na uptake together with a concomitant increase in P, N and Mg absorption and high chlorophyll content in mycorrhizal plants may be important salt-alleviating mechanisms for plants growing in saline soil.

Purification strategies for microbial lipases.

Microbial lipases today occupy a place of prominence among biocatalysts owing to their ability to catalyze a wide variety of reactions in aqueous and non-aqueous media. The chemo-, regio- and enantio-specific behaviour of these enzymes has caused tremendous interest among scientists and industrialists. Lipases from a large number of bacterial, fungal and a few plant and animal sources have been purified to homogeneity. This has enabled their successful sequence determination and their three-dimensional structure leading to a better understanding of their unique structure-function relationships during various hydrolytic and synthetic reactions. This article presents a critical review of different strategies which have been employed for the purification of bacterial, yeast and fungal lipases. Since protein purification is normally done in a series of sequential steps involving a combination of different techniques, the effect of sequence of steps and the number of times each step is used is analyzed. This will prove to be of immense help while planning lipase purification. Novel purification technologies now available in this field are also reviewed.