Non-mycorrhizal Plants Research Articles

Host age and surrounding vegetation affect the community and colonization rates of arbuscular mycorrhizal fungi in a temperate grassland.

Arbuscular mycorrhizal fungi (AMF) are important symbionts for the majority of terrestrial vascular plants, yet the drivers of the compositional variation in AMF communities need to be better understood. What effects does the ontogenetic stage of host plants have and do these effects differ between plant functional groups? Are the AMF communities modified by the properties of surrounding vegetation, such as the proportion of different functional groups or nonmycorrhizal plants ? We addressed these questions in a temperate grassland and studied AMF communities using next-generation sequencing and light microscopy, evaluating their composition, taxonomic, phylogenetic and functional diversity, functional traits and root colonization levels. We found important differences between AMF communities and their diversity between seedlings and adults which are larger than the differences among host species or between functional groups. The proportion of nonmycorrhizal plants in the surrounding affected AMF community composition and increased its richness. Our results highlight the need for further investigating the existence of a common mycelial networks. The decision to use seedlings for experimental work can affect the results more than the chosen host species.

The effect of arbuscular mycorrhizal fungi on the phenolic compounds profile, antioxidant activity and grain yields in wheat cultivars growing under hydric stress.

Hydric stress affects the production of wheat (Triticum aestivum L.) worldwide, making some tools necessary to cope with the decrease in rainfall. A sustainable alternative is the use of arbuscular mycorrhizal fungi (AMF) as biofertilisers. Here, we analysed the effects of AMF strains adapted or non-adapted to hyper-arid conditions on the phenolic profiles and antioxidant activities of wheat grains from two cultivars with contrasting tolerance to osmotic stress (Ilustre, moderately tolerant; and Maxi, tolerant) grown with and without hydric stress. Eight phenolic compounds were detected, apigenin-C-pentoside-C-hexoside I being the most abundant and showing an increase of 80.5% when inoculated with the fungus Funneliformis mosseae (FM) obtained from Atacama Desert under normal irrigation with respect to non-mycorrhizal (NM) plants. NM treatments were associated with higher grain yields. FM showed a noticeable effect on most phenolic compounds, with an increase up to 30.2% in apigenin-C-pentoside-C-hexoside III concentration under hydric stress with respect to normal irrigation, being also responsible for high antioxidant activities such as ABTS (2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) and DPPH (2,2-diphenyl-1-picrylhydrazyl) activities. Inoculation with FM adapted to hydric stress produced improvements in phenolics composition and antioxidant activities in grains from wheat plants growing under hydric stress conditions, improving their food quality and supporting the development of further studies to determine whether the use of adapted AMF could be a realistic tool to improve grain quality in a scenario of increasing hydric stress conditions. © 2021 Society of Chemical Industry.

Pisolithus tinctorius extract affects the root system architecture through compound production with auxin-like activity in Arabidopsis thaliana.

Pisolithus tinctorius is an ectomycorrhizal fungus that has been used worldwide as an inoculant to promote the growth and health of plant roots of forest importance. P. tinctorius has capacity to form symbiosis which mycorrhizal plants through the production of phytohormones, indole-3-acetic acid (IAA) the main auxin produced by these ectomycorrhizal fungi modulating root system architecture by inducing lateral root formation and root hair elongation in host plants of tree forest. However, the inoculant or compounds produced by P. tinctorius have not been evaluated in non-mycorrhizal plants. In the present study, we evaluated the effects of crude extracts of the P. tinctorius (CEPt) culture supernatant using Arabidopsis thaliana as plant model system to elucidate the molecular mechanisms of plant growth in non-host plant. Our results suggest that the crude extract of the supernatant produced by P. tinctorius has the ability to induce plant growth and root system architecture in Arabidopsis seedlings through the production of compounds with auxin-like activity, inducing the expression of DR5::uidA and BA3::uidA Arabidopsis line reporter of auxin responses and required an intact auxin signaling pathway, to modulate the plant growth in Arabidopsis seedlings.

Mycorrhizal growth and phosphorus responses of tomato differ with source but not application rate of phosphorus fertilisers

Phosphorus (P) can be added to the soil from various sources (e.g., chemical fertilisers and organic materials), and P fertilisation affects mycorrhizal colonisation and function in plants. While arbuscular mycorrhizal symbiosis is an integral part of most crop plants, there is a gap in understanding mycorrhizal growth and nutrition responses in relation to different sources of P at similar and variable application rates. Here we explore the impacts of different P sources (solely inorganic, mixed, or solely P-rich organic material), applied at three P application rates, on plant growth, nutrition and mycorrhizal responses. Tomato plants (arbuscular mycorrhizal and non-mycorrhizal plants) were grown in a soil amended with 10, 20 and 40 mg P kg−1. We found that the solely inorganic P source affected mycorrhizal and non-mycorrhizal plants differently to the solely P-rich organic source, as did the combination of the two, even with P application rates matched between different sources. The solely inorganic P source consistently favoured mycorrhizal plants, whereas mycorrhizal plants performed less successfully than non-mycorrhizal plants in the solely P-rich organic source. However, mycorrhizal and non-mycorrhizal plants responded equally in the soil where the mixed P source was added. The results indicated that blending inorganic and organic P sources could be used to mitigate negative effects of AMF on plant growth and P nutrition compared to using solely P-rich organic material.

English

Studies have shown arbuscular mycorrhizal fungi (AMF) enhance phosphorus (P) uptake and drought tolerance in maize (Zea mays L.) grown in semiarid soils. However, little is known regarding the contribution of AMF to maize treated with different levels of phosphorus and grown in different soil moisture levels. This study was conducted to determine the effects of AMF (Glomus fasciculatum) inoculation on growth and P uptake of maize treated with different levels of soil P and soil moisture. Different P levels (0, 50, and 100 kg P ha-1) were applied on maize grown in soils with and without mycorrhizal fungi, and at different moisture levels producing -0.05, -0.4, -0.8, and -1.5 MPa of drought stress. Increasing P rates significantly (p < 0.05) reduced mycorrhizal colonization. Mycorrhizal colonization was higher under moderate than under lower soil moisture levels. Drought stress × soil P content × AMF inoculation interaction had significant (p < 0.05) effect on maize shoot and root dry weight and tissue P concentration. Overall, results of this study suggest that mycorrhizal inoculation enhances P uptake and maximizes maize biomass under low, moderate, and high soil moisture conditions without P applications. Except for the lowest soil moisture level (-1.5 MPa), mycorrhizal plants produced higher biomass, with greater tissue P content than nonmycorrhizal plants at all soil P and soil moisture levels. These results indicate that establishing efficacious AMF with maize could be an efficient alternative for growers than relying on P fertilizer application and its associated costs and environmental concerns. Keywords: Arbuscular Mycorrhiza Fungi, Drought Tolerance, Phosphorus Levels, Maize Plants.

Use of the Glomus etunicatum as biocontrol agent of the soybean cyst nematode

This study investigated the effect of arbuscular mycorrhiza (Glomus etunicatum Becker & Gerd.), on the cyst nematode (Heterodera glycines Ichinohe), in a greenhouse. Mycorrhizal and non-mycorrhizal soybean plants were exposed to the pathogen at different initial population densities (0, 500, 1000, 2000, and 4000 nematodes eggs). Soybean growth, nematode reproduction, and the arbuscular mycorrhizal fungus’s capacity to decrease disease pressure were determined after 60 day-olds. The height of the plants was increased by 26% in the presence of arbuscular mycorrhizal fungus (AMF) despite of a higher initial population of cyst nematodes. The root length was, on average, 32.20% was greater in the presence of AMF. The number of nematodes females found in the root system of mycorrhizal plants was 28.21% lower than in non-mycorrhizal roots. These results suggest that AMF G. etunicatum acts indirectly, promoting an improvement in the nutritional plant status creating tolerance to the presence of the pathogen by soybean.

Mycorrhiza-Induced Resistance against Foliar Pathogens Is Uncoupled of Nutritional Effects under Different Light Intensities.

The use of microbial inoculants, particularly arbuscular mycorrhizal fungi, has great potential for sustainable crop management, which aims to reduce the use of chemical fertilizers and pesticides. However, one of the major challenges of their use in agriculture is the variability of the inoculation effects in the field, partly because of the varying environmental conditions. Light intensity and quality affect plant growth and defense, but little is known about their impacts on the benefits of mycorrhizal symbioses. We tested the effects of five different light intensities on plant nutrition and resistance to the necrotrophic foliar pathogen Botrytis cinerea in mycorrhizal and non-mycorrhizal lettuce plants. Our results evidence that mycorrhiza establishment is strongly influenced by light intensity, both regarding the extension of root colonization and the abundance of fungal vesicles within the roots. Light intensity also had significant effects on plant growth, nutrient content, and resistance to the pathogen. The effect of the mycorrhizal symbiosis on plant growth and nutrient content depended on the light intensity, and mycorrhiza efficiently reduced disease incidence and severity under all light intensities. Thus, mycorrhiza-induced resistance can be uncoupled from mycorrhizal effects on plant nutrition. Therefore, mycorrhizal symbioses can be beneficial by providing biotic stress protection even in the absence of nutritional or growth benefits.

Soil Zn Fertilization and Inoculation with Arbuscular Mycorrhizal Fungus and Azotobacter Chroococcum Bacteria Affect the Cd Concentration and Zn Bioavailability in Bread Wheat Grown in a Cd-spiked Soil

ABSTRACT Wheat is the main staple crop in Iran and thus of critical importance in human nutrition. This study was conducted to investigate the effect of individual and co-inoculation of azotobacter chroococcum bacteria (A. chroococcum) and a species (Rhizophagus irregularis) of arbuscular mycorrhizal fungi (AMF) on improving the nutritional quality of bread wheat grain. We performed a pot experiment, in which the effects of R. irregularis and A. chroococcum inoculation, and zinc (Zn) fertilization [0, 4.4, and 8.8 mg (kg)−1] to cadmium (Cd)-spiked soil on increasing the Zn bioavailability and reducing the Cd concentration of wheat grains were tested. Inoculation with A. chroococcum increased the rate of root colonization by R. irregularis. Root colonization with AM fungus significantly reduced the grain Cd concentration especially after co-inoculation with A. chroococcum and soil application of ZnSO4 fertilizer. Mycorrhized plants, compared to non-mycorrhized plants had considerably higher grain concentrations of phosphorous (P) and nitrogen (N), which were affected by the application rate of ZnSO4 and co-inoculation with A. chroococcum. The response of grain Zn concentration to mycorrhization was dependent on the rate of Zn fertilization and inoculation with A. chorococum. Single inoculation with R. irregularis increased the concentration of phytic acid (PA) and also the molar ratio of PA:Zn in grains, which may have resulted in reduced Zn bioavailability. In contrast, double inoculation of plants with R. irregularis and A. chroococcum reduced the molar ratio of PA:Zn especially after application of ZnSO4. This study suggests that dual inoculation of wheat plants with A. chroococcum and R. irregularis together with Zn fertilization may enhance the nutritional quality of wheat grains.

Mycorrhizal symbiosis primes the accumulation of antiherbivore compounds and enhances herbivore mortality in tomato.

Plant association with arbuscular mycorrhizal fungi (AMF) can increase their ability to overcome multiple stresses, but their impact on plant interactions with herbivorous insects is controversial. Here we show higher mortality of the leaf-chewer Spodoptera exigua when fed on tomato plants colonized by the AMF Funneliformis mosseae, evidencing mycorrhiza-induced resistance. In search of the underlying mechanisms, an untargeted metabolomic analysis through ultra-performance liquid chromatography tandem mass spectrometry (UPLC-MS) was performed. The results showed that mycorrhizal symbiosis had a very limited impact on the leaf metabolome in the absence of stress, but significantly modulated the response to herbivory in the damaged area. A cluster of over accumulated metabolites was identified in those leaflets damaged by S. exigua feeding in mycorrhizal plants, while unwounded distal leaflets responded similar to those from non-mycorrhizal plants. These primed-compounds were mostly related to alkaloids, fatty acid derivatives and phenylpropanoid-polyamine conjugates. The deleterious effect on larval survival of some of these compounds, including the alkaloid physostigmine, the fatty acid derivatives 4-oxododecanedioic acid and azelaic acid, was confirmed. Thus, our results evidence the impact of AMF on metabolic reprograming upon herbivory that leads to a primed accumulation of defensive compounds.

Acaulospora longula Spain & N.C. Schenck: A low-cost bioinsumption to optimize phenolics and saponins production in Passiflora alata Curtis

The arbuscular mycorrhizal fungi (AMF) inoculation is an alternative to regulate the synthesis of plant biomolecules, such as the flavonoids and saponins, which confer therapeutic properties in Passiflora. With such benefits, Passiflora alata can have its phytomass improved, increasing the interest of sedative herbal medicine industries. Thus, this study aimed to select the most efficient AMF on increasing the phenolic compounds and saponins production in P. alata. In foliar ethanolic extracts, the production of saponins and total phenols were increased by 137.93 % and 110.75 %, respectively, in seedlings associated with A. longula in comparison to non-inoculated plants. In this same treatment, we verified an increment of 219.96 % in the total soluble carbohydrates, in addition to an increase in the leaf area (589.20 %) and stem diameter (13.92 %), in comparison to non-mycorrhizal plants. The foliar phenols production and the plant growth were also benefited in plants inoculated with G. albida, nonetheless, at lower increments. On the other hand, the production of proteins, flavonoids, proanthocyanidins and the antioxidant activity was not favored by AMF inoculation. Therefore, A. longula is the most efficient AMF to obtain greater metabolites concentration of medicinal interest in sweet passion fruit phytomass.

Effects of Funneliformis mosseae on the utilization of organic phosphorus in Camellia oleifera Abel.

Arbuscular mycorrhizal (AM) fungi play an important role in the acquisition of phosphorus(P) by plants. The external hyphae of AM fungi function as an extension of plant roots and may downregulate related functions in the roots. It is not clear whether the ability of AM fungi to mineralize organicP affects root phosphatase activities. A pot experiment was conducted to investigate the effect of Funneliformis mosseae on soil organicP mineralization under phytate application and to explore root phosphatase activities, Puptake, and growth in Camellia oleifera Abel. The plants and their growth substrates were harvested 4 and 8months after planting. The results showed that organicP application had no effect on the total dry mass of nonmycorrhizal plants, but differences in dry mass under P application were observed in mycorrhizal plants in both harvests. Inoculation with F.mosseae increased soil acid phosphatase, phytase, and alkaline phosphatase activities and reduced the soil organicP content. Mycorrhizal plants had higher root activity, shoot and root P contents and root acid phosphatase and phytase activities than nonmycorrhizal plants irrespective of organicP application. In conclusion, AM fungi enhanced the mineralization of soil organicP and positively affect root phosphatase activities.

Arbuscular Mycorrhizal Fungi Alleviate Drought Stress in Trifoliate Orange by Regulating H+-ATPase Activity and Gene Expression.

A feature of arbuscular mycorrhiza is enhanced drought tolerance of host plants, although it is unclear whether host H+-ATPase activity and gene expression are involved in the physiological process. The present study aimed to investigate the effects of an arbuscular mycorrhizal fungus (AMF), Funneliformis mosseae, on H+-ATPase activity, and gene expression of trifoliate orange (Poncirus trifoliata) seedlings subjected to well-watered (WW) and drought stress (DS), together with the changes in leaf gas exchange, root morphology, soil pH value, and ammonium content. Soil drought treatment dramatically increased H+-ATPase activity of leaf and root, and AMF inoculation further strengthened the increased effect. A plasma membrane (PM) H+-ATPase gene of trifoliate orange, PtAHA2 (MW239123), was cloned. The PtAHA2 expression was induced by mycorrhization in leaves and roots and also up-regulated by drought treatment in leaves of AMF-inoculated seedlings and in roots of AMF- and non-AMF-inoculated seedlings. And, the induced expression of PtAHA2 under mycorrhization was more prominent under DS than under WW. Mycorrhizal plants also showed greater photosynthetic rate, stomatal conductance, intercellular CO2 concentration, and transpiration rate and better root volume and diameter than non-mycorrhizal plants under DS. AMF inoculation significantly increased leaf and root ammonium content, especially under DS, whereas it dramatically reduced soil pH value. In addition, H+-ATPase activity was significantly positively correlated with ammonium contents in leaves and roots, and root H+-ATPase activity was significantly negatively correlated with soil pH value. Our results concluded that AMF stimulated H+-ATPase activity and PtAHA2 gene expression in response to DS, which resulted in great nutrient (e.g., ammonium) uptake and root growth, as well as low soil pH microenvironment.

Partial overlap of fungal communities associated with nettle and poplar roots when co-occurring at a trace metal contaminated site

Stinging nettle (Urtica dioica L.) raises growing interest in phytomanagement because it commonly grows under poplar Short Rotation Coppices (SRC) set up at trace-metal (TM) contaminated sites and provides high-quality herbaceous fibres. The mycobiome of this non-mycorhizal plant and its capacity to adapt to TM-contaminated environments remains unknown. This study aimed at characterizing the mycobiome associated with nettle and poplar roots co-occurring at a TM-contaminated site. Plant root barcoding using the fungi-specific ITS1F-ITS2 primers and Illumina MiSeq technology revealed that nettle and poplar had distinct root fungal communities. The nettle mycobiome was dominated by Pezizomycetes from known endophytic taxa and from the supposedly saprotrophic genus Kotlabaea (which was the most abundant). Several ectomycorrhizal fungi such as Inocybe (Agaricomycetes) and Tuber (Pezizomycetes) species were associated with the poplar roots. Most of the Pezizomycetes taxa were present in the highly TM-contaminated area whereas Agaricomycetes tended to be reduced. Despite being a known non-mycorrhizal plant, nettle was associated with a significant proportion of ectomycorrhizal OTU (9.7%), suggesting some connexions between the poplar and the nettle root mycobiomes. Finally, our study raised the interest in reconsidering the fungal networking beyond known mycorrhizal interactions.

Physiological responses of mycorrhizal symbiosis to drought stress in white clover

The aim of the present study was to analyze the effects of two arbuscular mycorrhizal fungi (AMF), Funneliformis mosseae and Paraglomus occultum, on leaf water status, root morphology, root sugar accumulation, root abscisic acid (ABA) levels, root malondialdehyde (MDA) content, and root antioxidant enzyme activities in white clover (Trifolium repens L.) exposed to well-watered (WW) and drought stress (DS) conditions. The results showed that root colonization by F. mosseae and P. occultum was significantly decreased by 7-week soil drought treatment. Under drought stress conditions, mycorrhizal fungal treatment considerably stimulated root total length, surface area and volume, as compared with non-mycorrhizal controls. In addition, inoculation with arbuscular mycorrhizal fungi also increased leaf relative water content and accelerated the accumulation of root glucose and fructose under drought stress. Mycorrhizal plants under drought stress registered higher activities of superoxide dismutase (SOD), catalase (CAT), and peroxidase (POD) and ABA levels in roots, while lower MDA contents, relative to non-mycorrhizal plants. As a result, mycorrhiza-inoculated plants represented better physiological activities (e.g. antioxidant defense systems, root morphology, and sugar accumulation) than non-inoculated plants in response to soil drought, whilst P. occultum had superior effects than F. mosseae.

Lime-rich and lime-poor coastal dunes: Natural blowout activity differs with sensitivity to high N deposition through differences in P availability to the vegetation

In industrialized countries, biodiversity is threatened by high atmospheric N deposition. In coastal dunes, blowouts can mitigate this through deposition of fresh sand, but lime-rich and lime-poor dunes may differ in blowout activity. We studied natural blowout activity and explanatory factors in 2000 and 2014 in up to 51 sites along the Dutch coast, representative for other parts of Europe. We further analyzed plant and soil characteristics related to P nutrition in seven sites in 2019 and found that blowout activity was intrinsically linked to interactions between the geosphere, pedosphere and biosphere. Blowout activity was higher in lime-rich than in lime-poor dunes, especially in 2014. This difference could not be explained by wind velocity and only partly by position in the landscape, but was associated with pH, critical N load and rabbit density. At high pH, P availability to the vegetation was low. Arbuscular mycorrhizal (AM) plant species thus predominated, which belong to the most characteristic dune plants and may provide rabbit food of better quality than nonmycorrhizal (NM) or ericoid mycorrhizal (ErM) plants. Root biomass was also low at high pH, which may reduce cohesion of the sand and increase blowout activity, especially in areas with high rabbit density. At low pH, P availability increased, which favored NM and ErM rather than AM plants, and root biomass increased, which increased stability of the blowouts. As a restoration measure, (re)activation of blowouts may improve buffer capacity, characteristic biodiversity and conservation status of coastal dune grasslands. However, lime-poor dunes are more vulnerable to acidification, increase in P availability and blowout stabilization than lime-rich dunes. In extremely lime-poor dunes, it may even be better to let vegetation develop towards Dune heathlands, which are also EU priority habitats.

Compatible Mycorrhizal Types Contribute to a Better Design for Mixed Eucalyptus Plantations.

Mixed-species forest plantation is a sound option to facilitate ecological restoration, plant diversity and ecosystem functions. Compatible species combinations are conducive to reconstruct plant communities that can persist at a low cost without further management and even develop into natural forest communities. However, our understanding of how the compatibility of mycorrhizal types mediates species coexistence is still limited, especially in a novel agroforestry system. Here, we assessed the effects of mycorrhizal association type on the survival and growth of native woody species in mixed-species Eucalyptus plantations. To uncover how mycorrhizal type regulates plant-soil feedbacks, we first conducted a pot experiments by treating distinct mycorrhizal plants with soil microbes from their own or other mycorrhizal types. We then compared the growth response of arbuscular mycorrhizal plants and ectomycorrhizal plants to different soil microbial compositions associated with Eucalyptus plants. We found that the type of mycorrhizal association had a significant impact on the survival and growth of native tree species in the Eucalyptus plantations. The strength and direction of the plant-soil feedbacks of focal tree species depended on mycorrhizal type. Non-mycorrhizal plants had consistent negative feedbacks with the highest survival in the Eucalyptus plantations, whereas nitrogen-fixing plants had consistent positive feedbacks and the lowest survival. Arbuscular mycorrhizal and ectomycorrhizal plants performed varied feedback responses to soil microbes from distinct mycorrhizal plant species. Non-mycorrhizal plants grew better with Eucalyptus soil microbes while nitrogen-fixing plants grew worse with their own conspecific soil microbes. Different soil microbial compositions of Eucalyptus consistently increased the aboveground growth of arbuscular mycorrhizal plants, but the non-mycorrhizal microbial composition of the Eucalyptus soil resulted in greater belowground growth of ectomycorrhizal plants. Overall, Eucalyptus plants induced an unfavorable soil community, impeding coexistence with other mycorrhizal plants. Our study provides consistent observational and experimental evidence that mycorrhizal-mediated plant-microbial feedback on species coexistence among woody species. These findings are with important implications to optimize the species combinations for better design of mixed forest plantations.

The cellulolytic activity and symbiotic potential of dark septate endophytic fungus Phialocephala fortinii to promote non-mycorrhizal plants growth

The endophytic fungi have attracted much attention to investigating their ability to degrade cellulose and promote plant growth as double functional roles. The objective of this study was to investigate the cellulase activity and the ability of dark septate endophytic fungus (DSE) Phialocephala fortinii to promote non-mycorrhizal plants. This study consisted of carboxy-methylcellulose degradation activity of DSE isolates, cellulase activity, and the effect of cellulolytic DSE to promote non-mycorrhizal plants growth assays. The results showed P. fortinii III.Pi.I8 had the largest cellulolytic index than P. fortinii CKG.II.10.1 and P. eryngii for 7 days of incubation time. The cellulase activity pattern of all P. fortinii isolates was rather similar to P. eryngii for the incubation time of 7 to 35 days. Phialocephala fortinii III.Pi.I8, CKG.II.10.1, and CKG.I.11 increased the growth of Brassica oleracea var. capitata by 7.63, 92.5, and 47.7%, and Spinacia oleracea by 58.5, 283, and 303%, respectively, over to the control plant. Heavy colonization of P. fortinii occurred both in B. oleracea var. capitata and S. oleracea roots. This study proved that although P. fortinii has cellulase activity but did not cause disease symptoms in non-mycorrhizal plants so that it can potentially be multifunctional as cellulose decomposer and plant growth promoter.

Inoculation with Clariodeoglomus etunicatum improves leaf food quality of tea exposed to P stress

The present study aimed to evaluate the effect of an arbuscular mycorrhizal fungus (AMF), Clariodeoglomus etunicatum, on leaf food quality and relevant gene expression levels of tea (Camellia sinensis cv. ‘Fuding Dabaicha’) seedlings exposed to 0.5 μM P (P0.5) and 50 μM P (P50) levels. Twenty-four weeks later, the seedlings recorded higher root mycorrhizal fungal colonization in P50 than in P0.5. AMF-inoculated tea plants represented significantly higher leaf fructose and glucose contents and lower sucrose content than non-inoculated plants, irrespective of substate P levels. AMF treatment also increased total amino acids content in P0.5 and P50, accompanied with higher expression of glutamate dehydrogenase (CsGDH) and lower expression of glutamine synthetase (CsGS) and glutamine oxoglutarate aminotransferase (CsGOGAT). The total flavonoid content was higher in mycorrhizal versus non-mycorrhizal plants under P0.5 and P50, together with induced expression of phenylalanine ammonia-lyase (CsPAL) and cinnamic acid 4-hydroxylase (CsC4H). Mycorrhizal fungal inoculation improved catechins content, which is due to the up-regulated expression of flavanone 3-hydroxylase (CsF3H), flavonoid 3'-hydroxylase (CsF3'H), dihydroflavonol 4-reductase (CsDFR), leucoanthocyanidin reductase (CsLAR), anthocyanidin reductase (CsANR), and chalcone isomerase (CsCHI) under P0.5. However, under P50, the gene involved in catechins synthesis was not affected or down-regulated by mycorrhization, implying a complex mechanism (e.g. nutrient improvement). AMF also inhibited the tea caffeine synthase 1 (CsTCS1) expression regardless of P levels. Therefore, the results of this study concluded that inoculation with C. etunicatum improves leaf food quality of tea exposed to P stress, but the improved mechanisms were different between P0.5 and P50.

Arbuscular Mycorrhizal Fungi Regulate Polyamine Homeostasis in Roots of Trifoliate Orange for Improved Adaptation to Soil Moisture Deficit Stress.

Soil arbuscular mycorrhizal fungi (AMF) enhance the tolerance of plants against soil moisture deficit stress (SMDS), but the underlying mechanisms are still not fully understood. Polyamines (PAs) as low-molecular-weight, aliphatic polycations have strong roles in abiotic stress tolerance of plants. We aimed to investigate the effect of AMF (Funneliformis mosseae) inoculation on PAs, PA precursors, activities of PA synthases and degrading enzymes, and concentration of reactive oxygen species in the roots of trifoliate orange (Poncirus trifoliata) subjected to 15 days of SMDS. Leaf water potential and total chlorophyll levels were comparatively higher in AMF-inoculated than in non-AMF-treated plants exposed to SMDS. Mycorrhizal plants recorded a significantly higher concentration of precursors of PA synthesis such as L-ornithine, agmatine, and S-adenosyl methionine, besides higher putrescine and cadaverine and lower spermidine during the 15 days of SMDS. AMF colonization raised the PA synthase (arginine decarboxylase, ornithine decarboxylase, spermidine synthase, and spermine synthase) activities and PA-degrading enzymes (copper-containing diamine oxidase and FAD-containing polyamine oxidase) in response to SMDS. However, mycorrhizal plants showed a relatively lower degree of membrane lipid peroxidation, superoxide anion free radical, and hydrogen peroxide than non-mycorrhizal plants, whereas the difference between them increased linearly up to 15 days of SMDS. Our study concluded that AMF regulated PA homeostasis in roots of trifoliate orange to tolerate SMDS.

Is AMF inoculation an alternative to maximize the in vitro antibacterial activity of Libidibia ferrea extracts?

Arbuscular mycorrhizal fungi (AMF) are known to provide plant species with several benefits, such as an increased production of bioactive compounds. However, it is yet to be defined whether extracts of mycorrhizal plants are more efficient in vitro antibacterial actions when compared to non-mycorrhizal plants. We tested the hypothesis of whether or not, methanolic extracts of Libidibia ferrea fruits, from plants established in the field and inoculated with AMF, have higher antibacterial action when inoculated with Acaulospora longula, Claroideoglomus etunicatum or Gigaspora albida. In addition, native L. ferrea fruits collected from the Caatinga area were also tested. The extracts of L. ferrea fruits inoculated with A. longula had higher in vitro antibacterial action in relation to the extracts of fruits from non-inoculated plants (p <0.05) thus characterizing the first record of different antibacterial actions of plant extracts due to inoculation with AMF. The extracts of L. ferrea fruits inoculated with A. longula were more efficient in inhibiting growth of Gram-negative bacteria. The zone diameters of inhibition ranged from 2.48 % to 7.56 % larger than the zones of the non-inoculated L. ferrea fruit extracts. The inoculation of L. ferrea with AMF may represent an alternative way of producing fruits with different antibacterial activity.