AM Plants Research Articles

The Impact of the Arbuscular Mycorrhizal Fungi on Growth and Physiological Parameters of Cowpea Plants Grown under Salt Stress Conditions

A pot experiment was conducted to examine the effects of arbuscular mycorrhizal fungi on growth, nutrition and some physiological aspects of cowpea (Vigna unguiculata L.) plants grown at different salinity concentrations (0, 10, 15, 20, 25 and 30 mM NaCl). Under saline condition, arbuscular mycorrhizal fungal (AMF) inoculation significantly increased growth responses, photosynthetic pigments, nutrient contents, proline and total soluble protein of cowpea plants compared to non-AM ones. Those stimulations were related to the levels of mycorrhizal colonization in the associated plants. Interestingly, high proline, chlorophyll content and antioxidant enzymes in AM plants could be important for salt alleviation in plants growing in saline soils.Int J Appl Sci Biotechnol, Vol 4(3): 372-379

Arbuscular mycorrhizal fungi modify nutrient allocation and composition in wheat (Triticum aestivum L.) subjected to heat-stress

To evaluate the role of the AM symbiosis on nutrient allocation in Triticum aestivum L. cv. 1110 at different growth stages before and after heat-stress at anthesis. Measurements of plant biomass and grain yield at anthesis, grain-filling and maturity; determination of macro- and micronutrient concentrations in aboveground biomass; evaluation of AM fungal structures in roots and assessment of light-use efficiency of plants. AM increased grain number in wheat under heat-stress, and altered nutrient allocation and tiller nutrient composition. Heat increased number of arbuscules in wheat root, whereas number of vesicles and total colonization were unaffected. Heat increased photosystem II yield and the electron transfer rate, whereas non-photochemical quenching decreased during the first 2 days of heat-stress. Nutrient allocation and –composition in wheat grown under heat-stress were altered by AM symbiosis, which lowered the K/Ca ratio, whereas it was increased by heat-stress. The increased carbon availability in spikes at this developmental stage, related to the C sink strength of the AM symbiosis and its influence on source-sink relationships in the host-plant, resulted in increased number of grains in heat-stressed AM plants.

Arbuscular mycorrhizal symbiosis regulates physiology and performance of Digitaria eriantha plants subjected to abiotic stresses by modulating antioxidant and jasmonate levels.

This study evaluates antioxidant responses and jasmonate regulation in Digitaria eriantha cv. Sudafricana plants inoculated (AM) and non-inoculated (non-AM) with Rhizophagus irregularis and subjected to drought, cold, or salinity. Stomatal conductance, photosynthetic efficiency, biomass production, hydrogen peroxide accumulation, lipid peroxidation, antioxidants enzymes activities, and jasmonate levels were determined. Stomatal conductance and photosynthetic efficiency decreased in AM and non-AM plants under all stress conditions. However, AM plants subjected to drought, salinity, or non-stress conditions showed significantly higher stomatal conductance values. AM plants subjected to drought or non-stress conditions increased their shoot/root biomass ratios, whereas salinity and cold caused a decrease in these ratios. Hydrogen peroxide accumulation, which was high in non-AM plant roots under all treatments, increased significantly in non-AM plant shoots under cold stress and in AM plants under non-stress and drought conditions. Lipid peroxidation increased in the roots of all plants under drought conditions. In shoots, although lipid peroxidation decreased in AM plants under non-stress and cold conditions, it increased under drought and salinity. AM plants consistently showed high catalase (CAT) and ascorbate peroxidase (APX) activity under all treatments. By contrast, the glutathione reductase (GR) and superoxide dismutase (SOD) activity of AM roots was lower than that of non-AM plants and increased in shoots. The endogenous levels of cis-12-oxophytodienoc acid (OPDA), jasmonic acid (JA), and 12-OH-JA showed a significant increase in AM plants as compared to non-AM plants. 11-OH-JA content only increased in AM plants subjected to drought. Results show that D. eriantha is sensitive to drought, salinity, and cold stresses and that inoculation with AM fungi regulates its physiology and performance under such conditions, with antioxidants and jasmonates being involved in this process.

Differential Effects of Cold Stress on the Antioxidant Response of Mycorrhizal and Non-Mycorrhizal Jatropha curcas (L.) Plants

Our main objective was to analyze the protection provided by Mycorrhiza (Rhizophagus intraradices) to Jatropha curcas plants under cold stress, through the analysis of physiological and oxidative stress parameters. Mycorrhizal (AM) and non-mycorrhizal (nonAM) plants were exposed to cold stress 4±1 oC temperature for 72 h. The control plant grow at 25 ±1 oC. Under cold stress, the stomata conductance decreased both AM and nonAM plants and photosynthetic efficiency only in non AM plants. The CAT activity increased in AM plants independently of stress conditions. GR activity shows a typical rise to cold stress in nonAM plants and decreased in AM ones. With cold stress, the APX activity was reduced in all treatments and SOD activity was not affected in all treatment The MDA content increased in nonAM plants while in AM plants it was unaffected by low temperature. This study reported on the regulation of antioxidant compounds, their relationship to the AM symbiosis and cold stress in Jatropha curcas L.

Arbuscular mycorrhiza inoculum reduces root respiration and improves biomass accumulation of salt-stressed Ulmus glabra seedlings

Contamination by de-icing salt can severely damage trees in urban areas. Arbuscular mycorrhizal fungi (AM) have been shown to increase plant resistance to excess salinity—mainly by improving nutrient uptake. However, the availability of AM symbionts is limited in urban soils. Because an increased carbon demand for root system maintenance could underlie restricted tree performance, beside well-known restraints to photosynthetic assimilation, this study focuses at possible ameliorating effects of commercial AM inoculum on the respiration of salt-stressed tree root systems.Ulmus glabra seedlings were grown in a well-fertilized sand peat mixture to minimize confounding effects aside from NaCl ion toxicity. Half of the seedlings were inoculated with commercial AM spores; after an establishment phase, some seedlings were treated with 50mM NaCl. Plant biomass allocation and fine root respiration were measured; root respiration was correlated to biomass accumulation.The salt treatment significantly reduced the biomass of non-inoculated seedlings; biomass of AM plants was not significantly affected by 50mM NaCl. Without NaCl stress the mycorrhizal plants tended to grow less than the non-inoculated due to the cost of having mycorrhiza—indicating that seedlings were not water or nutrient limited. Fine root respiration increased significantly only in the non-inoculated plants under salt stress. Total and root biomass both showed strong negative correlation with fine root respiration, indicating that the decrease in growth was caused by the higher root respiration of stressed plants.In summary, our results indicate that commercial AM inoculate can prevent a major increase of root respiration under moderate NaCl stress, enabling trees to deploy more assimilated C for growth and, theoretically, defence mechanisms against other stress factors occurring in urban environments. Thus, a valuable strategy to reduced salt-induced stress of arbuscular mycorrhized urban trees is to make sure sufficient symbionts are available, e.g. by artificially supplying commercial AM inoculum to planting pits.

The role of inoculum identity in drought stress mitigation by arbuscular mycorrhizal fungi in soybean

It is well known that arbuscular mycorrhizal fungi (AMF) effects on plant growth largely depend on fungus identity. The objective of this study was to test whether three individual AMF isolates and their mixture mitigate drought stress (DS) differentially in soybean (Glycine max) genotype, predicting that under DS, the mixture of the AMF isolates would provide greater benefits to soybean plants than individual ones. In a greenhouse experiment, a drought-susceptible soybean genotype was inoculated with Septoglomus constrictum, Glomus sp., and Glomus aggregatum, known to be among the most abundant in agricultural and natural soils from central Argentina, and their mixture (Mx). Whereas under well-watered (WW) conditions, individual isolates and Mx treatment were similarly infective; under DS conditions, the Mx treatment showed lower rates of root colonization. Between WW and DS conditions, biomass was decreased in all treatments, although this effect was more marked in non-AM plants. Moreover, AMF strains improved water content and P and N concentrations. Under DS, the Mx treatment was unable to exceed the highest contents that were recorded by AMF isolates. However, under WW conditions, the Mx treatment showed a higher N content than individual isolates. Under both watering conditions, AM plants reduced oxidative damage evaluated as malondiadehyde and chlorophyll content and keep constant osmotic metabolites such as soluble sugars and proline content, without significant differences between AMF isolates and the Mx treatment. These results show that AMF play an important role in mitigating drought impacts on soybean, but that mixtures of AMF isolates did not perform as well as the best single strain inoculum, excluding complementarity effects and suggesting selection effect of AMF on DS alleviation in soybean.

Arbuscular mycorrhizal effects on plant water relations and soil greenhouse gas emissions under changing moisture regimes

Increased nutrient and/or water uptake by AM symbiosis may affect soil biochemical properties and greenhouse gas (GHG) emissions. A greenhouse experiment was carried out to compare mycorrhizal tomato (76R MYC) and its non-mycorrhizal mutant (rmc) on the CO2 and N2O emissions from an organically-managed soil. Plants were grown for 10 weeks in pots with compost amended soil and subjected to two consecutive dry down cycles to simulate changing moisture regimes in the field. Dry downs were applied gradually through controlled watering treatments. The effects of AM and soil moisture in GHG emissions were assessed in root in-growth PVC cylinders installed in the pots. Gas samples were taken from the cylinders using static chambers 4 h after each watering event. Photosynthetic rates and stomatal conductance of the plants were assessed after watering using a field portable open flow infra-red gas analyzer. Soil moisture was monitored throughout the experiment. Plant biomass and total shoot N, P and K as well as soil content of DON, DOC, NH4+–N, NO3−–N and microbial biomass C, were assessed at harvest. For the same shoot growth and nutrient content, rmc plants allocated more resources to root biomass than mycorrhizal plants. AM symbiosis improved the capacity of the plants to adapt to changing soil moisture, increasing photosynthetic rates and stomatal conductance at high soil moisture but decreasing them when soil moisture was lower. In addition AM symbiosis helped to regulate N2O emissions at high soil moisture. Control over N2O emissions by AM plants seemed to be driven by a higher use of soil water and not by increased N uptake.

Arbuscular mycorrhiza and plant succesion on zinc smelter spoil heap in Katowice-Wełnowiec

Mycorrhizal status of plants colonising the zinc wastes in Katowice was surveyed. In total 69 vascular plant species (25 families) appearing on the investigated area have been noted. More than 60% of them were mycorrhizal. Non-mycorrhizal species, such as <em>Cardaminopsis arenosa</em> and <em>Silene vulgaris</em> dominated the early successional part of the zinc heap. <em>Tussilago farfara</em> was the only AM plant there, however, no arbuscules were developed at this stage. The number of AM species was increased on the 20 years old part of the zinc wastes and on the older 30-50 years old areas. AM plants constituted about 60% of the total number of species there. The frequency of particular AM species was the highest on the oldest part of the investigated area. The usefulness of the results for restoration practices was discussed.

Effect of different arbuscular mycorrhizal fungi on growth and physiology of maize at ambient and low temperature regimes.

The effect of four different arbuscular mycorrhizal fungi (AMF) on the growth and lipid peroxidation, soluble sugar, proline contents, and antioxidant enzymes activities of Zea mays L. was studied in pot culture subjected to two temperature regimes. Maize plants were grown in pots filled with a mixture of sandy and black soil for 5 weeks, and then half of the plants were exposed to low temperature for 1 week while the rest of the plants were grown under ambient temperature and severed as control. Different AMF resulted in different root colonization and low temperature significantly decreased AM colonization. Low temperature remarkably decreased plant height and total dry weight but increased root dry weight and root-shoot ratio. The AM plants had higher proline content compared with the non-AM plants. The maize plants inoculated with Glomus etunicatum and G. intraradices had higher malondialdehyde and soluble sugar contents under low temperature condition. The activities of catalase (CAT) and peroxidase of AM inoculated maize were higher than those of non-AM ones. Low temperature noticeably decreased the activities of CAT. The results suggest that low temperature adversely affects maize physiology and AM symbiosis can improve maize seedlings tolerance to low temperature stress.

Mycorrhizal-mediated lower proline accumulation in Poncirus trifoliata under water deficit derives from the integration of inhibition of proline synthesis with increase of proline degradation.

Proline accumulation was often correlated with drought tolerance of plants infected by arbuscular mycorrhizal fungi (AMF), whereas lower proline in some AM plants including citrus was also found under drought stress and the relevant mechanisms have not been fully elaborated. In this study proline accumulation and activity of key enzymes relative to proline biosynthesis (▵1-pyrroline-5-carboxylate synthetase, P5CS; ornithine-δ-aminotransferase, OAT) and degradation (proline dehydrogenase, ProDH) were determined in trifoliate orange (Poncirus trifoliata, a widely used citrus rootstock) inoculated with or without Funneliformis mosseae and under well-watered (WW) or water deficit (WD). AMF colonization significantly increased plant height, stem diameter, leaf number, root volume, biomass production of both leaves and roots and leaf relative water content, irrespectively of water status. Water deficit induced more tissue proline accumulation, in company with an increase of P5CS activity, but a decrease of OAT and ProDH activity, no matter whether under AM or no-AM. Compared with no-AM treatment, AM treatment resulted in lower proline concentration and content in leaf, root, and total plant under both WW and WD. The AMF colonization significantly decreased the activity of both P5CS and OAT in leaf, root, and total plant under WW and WD, except for an insignificant difference of root OAT under WD. The AMF inoculation also generally increased tissue ProDH activity under WW and WD. Plant proline content significantly positively correlated with plant P5CS activity, negatively with plant ProDH activity, but not with plant OAT activity. These results suggest that AM plants may suffer less from WD, thereby inducing lower proline accumulation, which derives from the integration of an inhibition of proline synthesis with an enhancement of proline degradation.

Alleviation of salt stress in citrus seedlings inoculated with arbuscular mycorrhizal fungi depends on the rootstock salt tolerance

Seedlings of Cleopatra mandarin (Citrus reshni Hort. ex Tan.) and Alemow (Citrus macrophylla Wester) were inoculated with a mixture of AM fungi (Rhizophagus irregularis and Funneliformis mosseae) (+AM), or left non-inoculated (−AM). From forty-five days after fungal inoculation onwards, half of +AM or −AM plants were irrigated with nutrient solution containing 50mM NaCl. Three months later, AM significantly increased plant growth in both Cleopatra mandarin and Alemow rootstocks. Plant growth was higher in salinized +AM plants than in non-salinized −AM plants, demonstrating that AM compensates the growth limitations imposed by salinity. Whereas AM-inoculated Cleopatra mandarin seedlings had a very good response under saline treatment, inoculation in Alemow did not alleviate the negative effect of salinity. The beneficial effect of mycorrhization is unrelated with protection against the uptake of Na or Cl and the effect of AM on these ions did not explain the different response of rootstocks. This response was related with the nutritional status since our findings confirm that AM fungi can alter host responses to salinity stress, improving more the P, K, Fe and Cu plant nutrition in Cleopatra mandarin than in Alemow plants. AM inoculation under saline treatments also increased root Mg concentration but it was higher in Cleopatra mandarin than in Alemow. This could explain why AM fungus did not completely recovered chlorophyll concentrations in Alemow and consequently it had lower photosynthesis rate than control plants. AM fungi play an essential role in citrus rootstock growth and biomass production although the intensity of this response depends on the rootstock salinity tolerance.

Alterations in Root Exudation of Intercropped Tomato Mediated by the Arbuscular Mycorrhizal Fungus Glomus mosseae and the Soilborne Pathogen Fusarium oxysporum f.sp. lycopersici

AbstractArbuscular mycorrhizal fungi (AMF) can control soilborne diseases such as Fusarium oxysporum f.sp. lycopersici (Fol). Root exudates play an important role in plant–microbe interactions in the rhizosphere, especially, in the initial phase of these interactions. In this work, we focus on (i) elucidating dynamics in root exudation of Solanum lycopersicum L. in an intercropping system due to AMF and/or Fol; (ii) its effect on Fol development in vitro; and (iii) the testing of the root exudate compounds identified in the chromatographic analyses in terms of effects on fungal growth in in vitro assays. GC‐MS analyses revealed an AMF‐dependent increase in sugars and decrease in organic acids, mainly glucose and malate. In the HPLC analyses, an increase in chlorogenic acid was evident in the combined treatment of AMF and Fol, which is to our knowledge the first report about an increase in chlorogenic acid in root exudates of AM plants challenged with Fol compared with plants inoculated with AMF only, clearly indicating changes in root exudation due to AMF and Fol. Root exudates of AMF tomato plants stimulate the germination rate of Fol, whereas the co‐inoculation of AMF and Fol leads to a reduction in spore germination. In the in vitro assays, citrate and chlorogenic acid could be identified as possible candidates for the reduction in Fol germination rate in the root exudates of the AMF+Fol treatment because they proved inhibition at concentrations naturally occurring in the rhizosphere.

How useful is the mutualism-parasitism continuum of arbuscular mycorrhizal functioning?

A recent review in this journal puts forward the premise that our recent studies have resulted in our questioning the validity of the so-called mutualism-parasitism continuum of functioning of arbuscular mycorrhizas. This premise is incorrect and appears largely to result from a misunderstanding of terminology. We clarify a comment in one of our publications that influenced the previous review, which contains several statements that do not accurately represent our views. Our research has overturned not the continuum concept itself, but some past ideas about the balance of resources traded between AM fungi and plants. Of course, we recognize that outcomes of AM symbiosis in relation to the non-mycorrhizal (NM) state are strongly influenced by many environmental factors. Nevertheless, underlying resource trade is always a key determinant of costs and benefits of the symbiosis for both partners. In this context, we address uncertainties and contradictory ideas about mechanisms, causes, effects and outcomes in AM symbioses that occur in the literature, and issues of relevance of research at different scales. We also discuss semantics that can cause confusion. Finally, we assess how useful the mutualism-parasitism continuum is for design of hypothesis-driven experiments to disentangle the complex interactions that determine growth of AM plants, i.e. the so-called emergent properties.

Native arbuscular mycorrhizal fungi isolated from a saline habitat improved maize antioxidant systems and plant tolerance to salinity

High soil salinity is a serious problem for crop production because most of the cultivated plants are salt sensitive, which is also the case for the globally important crop plant maize. Salinity stress leads to secondary oxidative stress in plants and a correlation between antioxidant capacity and salt tolerance has been demonstrated in several plant species. The plant antioxidant capacity may be enhanced by arbuscular mycorrhizal fungi (AMF) and it has been proposed that AM symbiosis is more effective with native than with collection AMF species. Thus, we investigated whether native AMF isolated from a dry and saline environment can help maize plants to overcome salt stress better than AMF from a culture collection and whether protection against oxidative stress is involved in such an effect. Maize plants inoculated with three native AMF showed higher efficiency of photosystem II and stomatal conductance, which surely decreased photorespiration and ROS production. Indeed, the accumulation of hydrogen peroxide, the oxidative damage to lipids and the membrane electrolyte leakage in these AM plants were significantly lower than in non-mycorrhizal plants or in plants inoculated with the collection AMF. The activation of antioxidant enzymes such as superoxide dismutase or catalase also accounted for these effects.

Effects of Mycorrhizal Colonization on Nitrogen and Phosphorus Leaching from Nursery Containers

Our goal was to investigate the effects of mycorrhizal colonization on nitrogen (N) and phosphorus (P) leaching from plants grown in nursery containers. We compared the growth response and the content of nitrate (NO3), ammonium (NH4), and orthophosphate, in leachates collected from mycorrhizal (AM) and nonmycorrhizal (NonAM) plants of the fast-growing perennial, Encelia californica Nutt. (california sunflower), and the slow-growing woody shrub, Rhus integrifolia (Nutt.) Brewer & S. Watson (lemonade berry). Plants were grown for 8 weeks with no fertilizer or with 0.88 g (half rate) and 1.76 g (full rate) of 18N–2.6P–9.9K Osmocote (18-6-12, 6–7 month longevity at 26 °C, Osmocote® controlled-release fertilizer; Scotts Co., Marysville, OH). Mycorrhizal colonization increased the growth and nutrient uptake of E. californica and R. integrifolia but was more effective at decreasing nutrient leaching from containers with E. californica. Mycorrhizal colonization contributed to reduce the content of NO3, NH4, and orthophosphate by up to 65% in leachates from E. californica grown with half rate of Osmocote and up to 70% to 80% in those from plants grown in full rates of Osmocote. In contrast, only the leachates from AM plants of R. integrifolia grown without fertilizer had generally lower nutrient content than those from NonAM plants. Leachates collected from AM plants grown in half rates of Osmocote had less P but no less N, and there were mostly no significant differences in the leachate content of NO3, NH4, and orthophosphate from AM and NonAM plants of R. integrifolia grown in full rates of Osmocote. However, mycorrhizal colonization reduced the fertilizer requirement to achieve maximum growth in both species. AM plants of E. californica and R. integrifolia grown with half rates of Osmocote had greater dry weight than the NonAM ones grown in full rates of Osmocote. Our study shows that mycorrhizal colonization can reduce N and P leaching either by increasing nutrient uptake or by allowing the use of lower fertilizer rates.

Interaction Effects of Arbuscular Mycorrhizal Fungi and Different Phosphate Levels on Growth Performance of Catharanthus roseus Linn.

Catharanthus roseus L. (Apocynaceae), a valuable medicinal plant with potential therapeutic value was inoculated with AM fungi Glomus fasciculatum under three different phosphate conditions. Catharanthus roseus plants raised in presence of the AM fungi showed increased growth in terms of (shoot length, root length, leaf number, fresh weight and dry weight). Total chlorophyll content and phosphate content of the shoot was found to be significantly higher in AM inoculated plants as compared to non AM Catharanthus plants. The activities of phosphatase enzymes were found to be increased in AM inoculated plants as compared to non AM plants. Root colonization percent was significantly higher in AM inoculated plants at zero and at all three phosphate levels after 60, 90 and 120 days of AM inoculation, but decreased at third phosphate level after 120 days of AM inoculation. The study suggests that Catharanthus roseus is dependent on the mycorrhizal fungi to a large extent for its growth and survival and also shows the potential of AM fungi Glomus fasciculatum in increasing growth and biomass of Catharanthus roseus L.

Effects of vesicular arbuscular mycorrhiza Glomus intraradices on photosynthetic pigments, antioxidant enzymes, lipid peroxidation, and chromium accumulation in maize plants treated with chromium

Contamination of soil and ground water by chromium (Cr), due to its wide industrial use, has become a serious source of concern over the past decade. In this study a glasshouse experiment was conducted to investigate the effects of the mycorrhizal fungus Glomus intraradices on Cr toxicity in maize plants. Half of the plants were inoculated with the arbuscular mycorrhizal fungus (AMF). Cr was supplied in the form of potassium dichromate at 0.00, 0.10, 0.25, and 0.50 mM through irrigation water in a sand culture. At the end of the experiment, it was observed that Cr had significantly decreased the chlorophyll content in the maize leaves. The mycorrhizal plants had greater chlorophyll content than the non-mycorrhizal plants. Moreover, increasing the chromium concentration caused an increase in the malondialdehyde (MDA) content in the shoots and roots of the whole plant; however, the AM plants showed a lower MDA content than the non-AM plants. Cr caused an induction in guaiacol peroxidase (GPX) and ascorbate peroxidase (APX) activity in the roots of the non-mycorrhizal plants but no significant induction was observed in APX activity in Cr-treated AM roots. The activity of GPX in the roots of AM plants was lower than in those of non-AM plants under chromium treatment. Measurements of chromium concentration indicated that Cr mainly accumulated in the roots of the maize plants. The Cr concentration significantly decreased in the shoots through AM symbiosis.

“Changes in antioxidant activity in Gmelina arborea (Verbenaceae) inoculated with Glomus fasciculatum under drought stress”

Gmelina arborea Roxb. seedlings were inoculated with arbuscular mycorrhizal fungi Glomus fasciculatum in a drought stress experiment. Irrigation was withheld after 30 days of AM inoculation and drought period were started. Control plants (non-AM and AM plants) were irrigated. Gmelina inoculated with Glomus fasciculatum grown under drought stress showed a significant increase in various morphological parameters like shoot and root length, fresh and dry weight as compared to non-AM inoculated Gmelina plants. Besides this, antioxidant activities (superoxide dismutase, guiacol peroxidase and catalase) were found to protect plants from drought stress. The relevance of the activities of these enzymes to drought stress indicates that AM inoculated Gmelina plants are found to be tolerant compared to non-AM inoculated Gmelina plants, which led us to conclude that AM treated Gmelina plants are sturdier and adaptive to stress conditions. These findings also suggest that association improves plant–water relations and contributes to drought tolerance in forest trees.

Differential occurrence of oxidative burst and antioxidative mechanism in compatible and incompatible interactions of Solanum lycopersicum and Ralstonia solanacearum

Striking increase in reactive oxygen species (ROS) such as hydrogen peroxide (H(2)O(2)) has been demonstrated to occur in plants in response to pathogen attack. The aim of this study was to investigate the biochemical aspects of ROS generation, antioxidative mechanism and cell wall reinforcement as responses of tomato cultivars Arka Meghali (AM; susceptible) and BT-10 (BT; resistant) against Ralstonia solanacearum (Ralsol). While the oxidative burst was characterized by a single phase ROS increase in AM, there was a clear bi-phasic ROS generation in BT. The first significant increase of H(2)O(2) production was noticed at 12h post-inoculation (hpi) followed by a sharp increase in H(2)O(2) generation after 36hpi. Lipid peroxidation was more in roots of AM than that of BT after pathogen inoculation. Superoxide dismutase and catalase activities were continuously at very high level in Ralsol-inoculated BT plants, whereas activities of the enzymes were observed to decrease at later stage in Ralsol-inoculated AM plants. Guaiacol peroxidase activity was high in Ralsol-inoculated roots of both cultivars, but BT recorded much higher activity than AM. Higher activity of ascorbate peroxidase in inoculated BT might be an indication of better scavenging activity of the enzyme. Total phenolic content and lignin deposition were significantly higher in Ralsol-inoculated BT compared to inoculated AM. Our results indicate that increased level of ROS production coupled with more efficient antioxidative system, lower rate of lipid peroxidation and high lignin deposition in cell wall may contribute to the resistance of tomato plants to Ralsol.

Effect of arbuscular mycorrhizal fungi inoculation on aster yellows phytoplasma-infected tobacco plants

The objective of the research was to asses if arbuscular mycorrhizal fungi (AM) can modify the effect of two aster yellows phytoplasma strains infection in tobacco plants. Tobacco plants experimentally inoculated with aster yellows phytoplasma strains did not develop visible disease symptoms. However, PCR examination indicated that the inoculated plants were phytoplasma infected. Mycorrhiza inoculation had a positive effect on the shoot height of healthy plants, but did not influence shoot growth and weight of phytoplasma-infected plants. The roots of all mycorrhiza-inoculated plants were slightly reduced but significant differences were found in the total root length of plants infected with the phytoplasma strain AY1. AM inoculation had a positive effect on photosynthetic activity of tobacco plants infected with the phytoplasma strain AYSim, but net photosynthesis of tobacco infected with the phytoplasma strain AY1 was decreased. Transpiration rate and calcium content of AM and phytoplasma-infected plants were not affected. The mechanisms underlying these interactions are discussed and a direct action of the AM fungus is hypothesized.