Influence of three vesicular-arbuscular mycorrhizal fungi (Glomaceae) on the activity of specific enzymes in the root system of Cucumis sativus L.

The influence of three vesicular-arbuscular mycorrhizal (VAM) Glomus species on the activity of enzymes in the roots of Cucumis sativus was tested. Cucumber plants were grown in a split-root system, in which colonized and uncolonized roots of a single plant could be separated. The activity of the host root malate dehydrogenase (MDH), glucose 6-phosphate dehydrogenase (Gd), glutamate oxaloacetate transaminase (GOT) and glutamate dehydrogenase (GDH) was measured on a densitometer after separation of the host and fungal enzymes on polyacrylamide gels.The results showed that only minor changes in the activity of the host root enzymes occurred after VAM inoculation. Gd was stimulated by VAM and phosphorus, and one of the fungi decreased the activity of GDH in the host plant when both parts of the root system were colonized.     

Growth and nutrient uptake of sorghum cultivated with vesicular-arbuscular mycorrhiza isolates at varying pH

This study was conducted to determine the effects of different pH regimes on root colonization with four vesicular-arbuscular mycorrhiza (VAM) isolates, and VAM effects on host plant growth and nutrient uptake. Sorghum [Sorghum bicolor (L.) Moench] was grown at pH 4.0, 5.0, 6.0 and 7.0 (±0.1) in hydroponic sand culture with the VAM isolates Glomus etunicatum UT316 (isolate E), G. intraradices UT143 (isolate I), G. intraradices UT126 (isolate B), and an unknown Glomus isolate with no INVAM number (isolate A). Colonization of roots with the different VAM isolates varied differentially with pH. As pH increased, root colonization increased with isolates B and E, remained unchanged with isolate I, and was low at pH 4.0 and high at pH 5.0, 6.0, and 7.0 with isolate A. Isolates E and I were more effective than isolates A and B in promoting plant growth irrespective of pH. Root colonization with VAM appeared to be independent of dry matter yields or dry matter yield responsiveness (dry matter produced by VAM compared to nonmycorrhizal plants). Dry matter yield responsiveness values were higher in plants whose roots were colonized with isolates E and I than with isolates A and B. Shoot P concentrations were lower in plants colonized with isolates E and I than with isolates A and B or nonmycorrhizal plants. This was probably due to the dilution effect of the higher dry matter yields. Neither the VAM isolate nor pH had an effect on shoot Ca, Mg, Zn, Cu, and Mn concentrations, while the VAM isolate affected not only P but also S, K, and Fe concentrations. The pH x VAM interaction was significant for shoot K, Mg, and Cu concentrations.     

Influence of phosphorus and formononetin on isozyme expression in the Zea mays‐Glomus intraradices symbiosis

Maize (Zea mays L. cv. Great Lakes 586) plants were either inoculated with the vesicular-arbuscular mycorrhizal (VAM) fungus Glomus intraradices Schenck and Smith, or grown in the presence of the isoflavone formononetin or were provided with both G. intraradices and formononetin. All plants were grown in soil containing one of five levels of inorganic P (between 8 and 110 µg g^?1 soil). By 3 weeks there were significant differences in a number of enzyme activities and in the pattern of isoenzymes in roots colonized by the VAM fungus or treated with formononetin. One NAD-malate dehydrogenase (MDH) isozyme was expressed only in mycorrhizal roots, whether treated or not with formononetin. Despite differences in the soil P level, the expression of this isozyme was not observed in non-mycorrhizal roots, indicating specific expression in the mycorrhizae. We suggest that MDH isozyme could serve as a specific, early indicator of the Zea-Glomus symbiosis. Differences in the esterase (EST) isozyme pattern were not detectable between VAM and non-VAM roots, suggesting that this enzyme system is not a good parameter for the evaluation of mycorrhizal colonization. As available P in the soil increased, total EST activity appeared to increase as well. Interestingly, total peroxidase (POX) activity increased along with P suggesting that as plant P nutrition improved, both cell wall ramification and the quantity of defense peroxidases increased as well. Total POX activity from mycorrhizal roots was inversely correlated with root colonization, indicating that there was suppression of POX activity by the host under low soil P. Most interestingly, formononetin further decreased POX activity regardless of the level of P or mycorrhizal status. This may suggest one mechanism by which formononetin enhances root VAM colonization. The presence of this isoflavone suppressed POX activity in mycorrhizal roots allowing a rapid penetration and spread of the fungus in the root cortex. The interplay between host root, soil P levels, secondary metabolites and endogenous host enzyme activities and a particular VAM fungus has a profound effect on the efficiency, duration and functioning of an endomycorrhizal symbiosis.     

Humid tropical leguminous tree and pasture grass responsiveness to vesicular-arbuscular mycorrhizal infection

Phosphorus is the major nutrient limiting plant growth in a Costa Rican silvopastoral system located on an acid, high P-retaining, volcanic soil. We investigated plant responsiveness to vesicular-arbuscular mycorrhizal (VAM) inoculation using the leguminous tree species Erythrina berteroana Urban, and the two dominant grass species Paspalum conjugatum Berg and Homolepsis aturensis Chase of this silvopastoral system. We grew grass seedlings in the greenhouse for 15 weeks in a methyl bromide-sterilized study soil to which either mixed-species VAM inoculum (Theobroma cacao feeder roots) or autoclave-sterilized cacao roots (non-inoculated control) were added. E. berteroana was grown from both seedlings and vegetative stakes (40 cm long) for 30 and 19 weeks, respectively. Upon harvest, we measured above and below ground biomass, N and P content, rootshoot ratio, legume nodulation, and VAM infection levels. The total above-ground and root biomass of mycorrhizae-inoculated P. conjugatum seedlings were 2.5 and 2.8 times greater than those of noninoculated seedlings. In contrast, VAM-inoculated seedlings of H. aturensis produced 8.4 and 5.9 times more total above-ground and root mass than noninoculated seedlings. Mycorrhizae-inoculated E. berteroana seedlings produced 10.6 times greater shoot biomass for inoculated versus noninoculated seedlings, while E. berteroana vegetative stakes exhibited a negative growth response to VAM inoculation (an approximately 16% decrease in shoot biomass for VAM-inoculated cuttings). The difference in responsiveness between Erythrina growth forms is hypothesized to reflect the cost-benefit relationship between plant host and fungal symbiont for energy and nutrient reserves.     

Seasonal dynamics of the association between sweet potato and vesicular-arbuscular mycorrhizal fungi

To better understand the behavior of selected vesicular-arbuscular mycorrhizal (VAM) isolates in the field, we documented the growth of roots, root hairs, and VAM colonization of inoculated and noninoculated sweet potato plants (Ipomea batatas (L.) Lam. cv White Star) over a growing season. We also determined the seasonal dynamics of P and Zn uptake, and shoot and storage-root growth. Shoot cuttings were inoculated with an isolate of either Glomus etunicatum Becker and Gerdemann or Acaulospora rugosa Mortan, or were not inoculated, and were harvested 2, 4, 8, 13, 20, and 27 weeks after planting (WAP). At each harvest, roots were sampled at 0 to 30, 30 to 60, and 60 to 90 cm depths and at 0, 23, 83, and 116 cm from the base of the shoot. At the end of the study, the roots of three non-inoculated plants were sampled by soil horizon. Inoculation had no affect on shoot growth or total shoot uptake of P and Zn; shoot dry mass and P and Z content increased rapidly up to 20 WAP, while shoot length continued to increase through 27 WAP. Shoot-P concentration of plants inoculated with A. rugosa at 2 and 8 WAP were higher than the noninoculated plants, while shoot-Zn concentration was not affected by inoculation. Storage-root yields of inoculated plants were higher than yields for noninoculated plants. Root length density, and percentage of root length with root hairs and VAM colonization were highest and most dynamic near the base of the plant. Percentage of root length colonization by VAM fungi was highest in the E2 horizon, intermediate in the Bh horizon, and lowest in the Ap horizon. Percentage of root length with root hairs had the opposite pattern. Intensive measurements of root characteristics close to the base of the plant, and shoot P-content and concentration during the period of rapid yield production, provided the most useful data for evaluating the activity of effective isolates.Published as Florida Agricultural Experimental Station Journal Series No. R-02576     

Modifications to clearing methods used in combination with vital staining of roots colonized with vesicular-arbuscular mycorrhizal fungi

Leek, maize, and pigmented soybean roots colonized by vesicular-arbuscular mycorrhizal (VAM) fungi were assessed for succinate dehydrogenase (SDH) activity using the nitro blue tetrazolium chloride (NBT)-succinate method. NBT-succinate-reacted roots, cleared in a 55° C drying oven in 5% (w/v) KOH for 24 h or longer and observed as whole mounts, revealed signs of intraradical VAM fungus colonization more clearly than roots cleared by the standard 20% (w/v) boiling chloral hydrate method. Combined clearing of NBT-succinate-reacted roots using boiling chloral hydrate followed by clearing in 5% KOH at 55° C for prolonged periods also improved the visualization of intraradical fungal structures. Bleaching of NBT-succinate-reacted roots using the standard NH₃-H₂O₂ method removed pigmentation from roots and did not alter the viability indicator, formazan. Pigmented, field-collected soybean roots were successfully cleared and bleached to reveal signs of viable and nonviable intraradical fungal structures. Counterstaining of NBT-succinate-reacted roots with acid fuchsin clearly revealed both viable and nonviable intraradical fungal structures. The NBT-succinate solution infiltrated all intraradical fungal structures after 24 h; formazan products were observed at similar concentrations in viable structures after 24, 36, and 48 h.     

Influence of edaphic and climatic factors on dynamics of root colonization and spore density of vesicular-arbuscular mycorrhizal fungi in Acacia farnesiana Willd. and A. planifrons W.et.A.

 A study was conducted to assess the dynamics of vesicular-arbuscular mycorrhizal (VAM) fungi associated with Acacia farnesiana and A. planifrons in moderately fertile alkaline soils. The intensity of root colonization by VAM fungi and the distribution of VAM fungal structures varied with host species over a period of time. The occurrence of vesicles with varied morphology in the mycorrhizal roots indicates infection by different VAM fungal species. This was further confirmed from the presence of spores belonging to different VAM fungal species in the rhizosphere soils. Root colonization and spore number ranged from 56% – 72% and 5 – 14 g^{–  1}soil in A. farnesiana and from 60% – 73% and 5 – 15 g^{–  1} soil in A. planifrons. Per cent root colonization and VAM spore number in the rhizosphere soil were inversely related to each other in both the Acacia species. However, patterns of the occurrence of VAM fungal structures were erratic. Spores of Acaulospora foveata, Gigaspora albida, Glomus fasciculatum, G. geosporum and Sclerocystis sinuosa were isolated from the rhizosphere of A. farnesiana whereas A. scrobiculata, G. pustulatum, G. fasciculatum, G. geosporum and G. microcarpum were isolated from that of A. planifrons. The response of VAM status to fluctuating edaphic factors varied with host species. In A. farnesiana though soil nitrogen (N) was positively correlated with root colonization, soil moisture, potassium and air temperature were negatively correlated to both root colonization and spore number. Per cent root colonization and spore number in A. planifrons were negatively related to each other. Further, in A. planifrons as the soil phosphorus and N were negatively correlated with the density of VAM fungal spores, the same edaphic factors along with soil moisture negatively influenced root colonization. Received: 16 May 1995 / Accepted: 7 February 1996     

Development of two endomycorrhizal symbioses on soybean and comparison with phosphorus fertilization

Summary Soybean (Glycine max L. Merr. cv. Amsoy 71) plants were grown in a greenhouse in a soil very low in plant-available P, and plants were harvested 5 times over a 21-week growth period. Soybeans were inoculated with one of two species of VAM fungi or received daily one of three nutrient solutions of different P concentrations (0.0, 0.2, or 1.0mMP). Until week 9, the dry weights, leaf areas and developmental stage of soybeans inoculated withG. fasciculatum orG. mosseae were similar to the 1.0 or 0.2mMP-treated plants, respectively. Phosphorus concentrations were significantly lower in VAM plants at weeks 6 and 9 as compared to non-VAM soybeans given 1.0mMP, suggesting P input in VAM plants was immediately used for new growth. Total P input for VAM plants was linear over 21 weeks, and the average rate of P uptake for these plants was 0.19mg P d⁻¹. Estimated specific P uptake rates (SPUR) for the mycorrhizae (VAM roots) were twice that of the control (0.0mMP) roots. The calculated SPURs forG. fasciculatum andG. mosseae hyphae were 95 and 120μg P g⁻¹ VAM d⁻¹ respectively, a 4 to 5 fold increase over non-inoculated roots, indicating more attention must be paid to P assimilation by VAM fungi in P-fixing substrates. Contribution from the Western Regional Research Center, USDA-ARS (CRIS No. 5325-20580-003).     

Occurrence of vesicular-arbuscular mycorrhizae in Pseudotsuga menziesii and Tsuga heterophylla seedlings grown in Oregon Coast Range soils

 Vesicular-arbuscular mycorrhizae (VAM) were common in seedlings of Pseudotsuga menziesii and Tsuga heterophylla grown in a greenhouse soil bioassay in soils collected from the Oregon Coast Range. Although root samples were heavily colonized by ectomycorrhizal fungi (EM), VAM colonization was observed in the cortical cells of both secondary and feeder roots. Vesicles, arbuscules, and hyphae typical of VAM occurred in 48% of 61 P. menziesii and 25% of 57 T. heterophylla seedlings. The ecological significance of VAM presence in the Pinaceae, as well as interactions among VAM, EM, and the plant host, deserve future investigation. Accepted: 16 August 1995     

Effects of a vesicular-arbuscular mycorrhizal fungus and other soil microorganisms on growth,mineral nutrient acquisition and root exudation of soil-grown maize plants

Maize (Zea mays L. cv. Alize) plants were grown in a calcareous soil in pots divided by 30-m nylon nets into three compartments, the central one for root growth and the outer ones for hyphal growth. Sterle soil was inoculated with either (1) rhizosphere microorganisms other than vesicular-arbuscular mycorrhizal (VAM) fungi, (2) rhizosphere microorganisms together with a VAM fungus [Glomus mosseae (Nicol. and Gerd.) Gerdemann and Trappel], or (3) with a gamma-irradiated inoculum as control. Plants were grown under controlled-climate conditions and harvested after 3 or 6 weeks. VAM plants had higher shootroot ratios than non-VAM plants. After 6 weeks, the concentrations of P, Zn and Cu in roots and shoots had significantly increased with VAM colonization, whereas Mn concentrations had significantly decreased. Root exudates were collected on agar sheets placed on the interface between root and hyphal compartments. Six-week-old VAM and non-VAM plants had similar root exudate compositions of 72–73% reducing sugars, 17–18% phenolics, 7% organic acids and 3% amino acids. In another experiment in which root exudates were collected on agar sheets with or without antibiotics, the amounts of amino acids and carbohydrates recovered were similar in VAM and non-VAM plants. However, threeto sixfold higher amounts of carbohydrates, amino acids and phenolics were recovered when antibiotics were added to the agar sheets. Thus, the high microbial activity in the rhizosphere and on the rhizoplane limits the exudates recovered from roots.     

Influence of temperature on colonization of spring barleys by vesicular arbuscular mycorrhizal fungi

The effects of three soil temperatures on growth of spring barleys (Hordeum vulgare L.) and on their root colonization by vesicular arbuscular mycorrhizal (VAM) fungi from agricultural soils in Montana (USA) or Syria at different inoculum concentrations were tested in soil incubators in the greenhouse. The number of mycorrhizal plants as well as the proportion and intensity of roots colonized increased with higher soil temperatures. VAM fungi from Montana, primarily Glomus macrocarpum, were cold tolerant at 11°C while those from Syria, primarily G. hoi, were heat tolerant at 26°C. Inoculum potential of Montana VAM fungi was higher than Syrian VAM fungi in cool soils. Harmal, selected from Syrian barley land races, had the highest colonization by mycorrhizal fungi of the cultivars tested.Journal Series Paper: J-2532 Montana Agricultural Experiment Station.     

Production of transgenic plants via Agrobacterium rhizogenes-mediated transformation of Panax ginseng

 Hairy roots of Panax ginseng were obtained after root disks were infected with wild-type strain Agrobacterium rhizogenes 15834. Three lines of hairy roots with different pigmentation were selected. Embryogenic callus was induced on Murashige and Skoog medium containing 1.0 mg/l 2,4-D. The frequency of embryogenic callus formation was 37.4% in a line with red pigmentation. Somatic embryo development from embryogenic callus was efficiently achieved by lowering the concentration of 2,4-D (0.5 mg/l). After the germination of somatic embryos on medium with 10 mg/l GA₃, the embryos were transferred to 1/2-MS medium without GA₃. The transformed ginseng plantlets had an actively growing root system with abundant lateral roots. The phenotypical alteration of transformed ginseng plants might be valuable character for increasing root yield. Received: 27 March 1999 / Revision received: 18 May 1999 / Accepted 8 July 1999     

Vesicular-arbuscular mycorrhizae in a wastewater-irrigated oldfield ecosystem in Michigan

The incidence of vesicular-arbuscular mycorrhizae (VAM) in wastewater irrigated and non-irrigated oldfield soils in Michigan was studied. Soil and root samples were taken monthly from field plots on the second and third years of consecutive irrigation with municipal wastewater at rates of 0, 5 and 10 cm wk^–1. The oldfield ecosystem contained a high VAM fungal spore population density, but low species diversity. The most common VAM fungal species were Glomus mosseae and G. fasciculatum. Both spore density and root colonization were higher in irrigated than in non-irrigated plots. Irrigation effects were largest early in the growing season. In addition to increasing VAM incidence, wastewater irrigation shifted VAM fungal species composition. Irrigation favored G. mosseae over G. fasciculatum. Bioassays using either Sorghum vulgare or Daucus carota, an oldfield native species, indicated that the VAM systems were still functioning after the third year of consecutive wastewater irrigation. The data from experiments using nutrient solutions at wastewater concentrations suggest that the effects of wastewater irrigation on VAM are due to the effects of both water and nutrients. Since VAM are a very important component of the plant's water and nutrient uptake system and equally important in structuring plant communities under limiting growth conditions, it is suggested that the stimulatory effect of wastewater irrigation on VAM in an oldfield ecosystem enhances the ecosystem's ability to function as a living filter for wastewater clean up.Michigan Agricultural Experimental Station Journal Article No 13137.On sabbatical leave from ESAL, Lavras-MG, Brazil     

Positive correlation between VAM-induced changes in root exudation and mycorrhizosphere mycoflora

The influence of vesicular-arbuscular mycorrhizal (VAM) fungi on rhizosphere mycoflora was studied together with the possible mechanism involved in this process. Six combinations of VAM fungi and phosphorus fertilizer treatments were applied to Leucaena leucocephala roots and quantitative and qualitative observations were made periodically of the rhizosphere mycoflora and constituents of root exudates. The results obtained indicate that the presence of specific mycoflora in the rhizosphere of mycrorrhizal roots is mediated through root exudates rather than being an outcome of improved P nutrition.     

Salinity and flooding stress effects on mycorrhizal and non-mycorrhizal citrus rootstock seedlings

Seedlings of the rootstocks Pineapple sweet orange (SwO), Carrizo citrange (CC), and sour orange (SO) were grown in low phosphorus (P) sandy soil and either inoculated with the vesicular-arbuscular mycorrhizal (VAM) fungus,Glomus intraradices, or were non-mycorrhizal (NM) and fertilized with P. VAM and NM seedings of similar shoot size and adequate P-status were selected for study of salinity and flooding stress. One-third of each of the VAM and NM plants were given 150 mM NaCl for a period of 24 days. One-third of the plants were placed into plastic bags and flooded for 21 days while the remaining third were non-stressed controls. In general, neither stress treatment affected mycorrhizal colonization. Salinity stress reduced the hydraulic conductivity of roots, leaf water potential, stomatal conductance and net assimilation of CO₂ (ACO₂) of mycorrhizal and non-mycorrhizal seedlings to a similar extent. VAM plants of CC and SO accumulated more Cl in leaves than NM plants. Cl was higher in non-mycorrhizal roots of SwO and CC than in mycorrhizal roots. Flooding the root zone for 3 weeks did not produce visible symptoms in the shoot but did influence plant water relations and reduce ACO₂ of all 3 rootstocks. VAM and NM plants of each rootstock were affected similarly by flooding. Comparable reduction in nitrogen and P content of both mycorrhizal and non-mycorrhizal plants suggested that flooding stress was primarily affecting root rather than hyphal nutrient uptake. Florida Agricultural Experimental Station Journal Series No. 7773.     

Alteration of growth ofSolanum opacum andPlantago drummondii and inhibition of regrowth of hyphae of vesicular-arbuscular mycorrhizal fungi from dried root pieces by manganese

Addition of MnSO₄ or MnCl₂ to a fine sandy soil from South Australia had a negative effect on shoot growth and root elongation ofSolanum opacum in the absence of significant presence of vesicular-arbuscular mycorrhiza (VAM). VAM ameliorated the reduction of plant growth by Mn, even though mycorrhizal development was decreased. Mn inhibited infection of roots by a fine endophyte less than that by some coarse endophytes. High concentrations of available Mn inhibited growth of hyphae of VAM fungi from dried root pieces, a significant source of infection by mycorrhizal fungi in the soil used.     

An image analysis method for determination of spatial colonization patterns of bacteria in plant rhizosphere

A method that allows the rapid visualization of bacterial spatial colonization patterns on roots for the determination of general colonization trends was developed. This method, which analyzes images of roots, and bioluminescence-enhanced images of bacterial colonization patterns on these roots, was used to study the colonization patterns of seed-applied Enterobacter cloacae strain E6 on 3-day-old cucumber plants. Conventional dilution-plating methods indicated that E6 colonized cucumber tap roots in high populations and that these populations significantly decreased as the distance from the seed increased. In addition to confirming these observations, image analysis indicated that colonization by E6 significantly decreased on lateral roots as the distance increased horizontally away from the tap root, and that this bacterium did not evenly cover the most densely colonized regions of the cucumber root system. Results from these experiments indicate that the majority of E6 populations on cucumber roots after seed application are limited to the upper regions of the tap root and that E6 does not effectively colonize other regions of the root system. Received: 15 June 1988 / Received revision: 19 November 1998 / Accepted: 29 November 1998     

Occurrence and importance of mycorrhizae in aquatic trees of New South Wales,Australia

Vesicular arbuscular mycorrhizal (VAM) infection was found in KOH-cleared and lactophenolblue-stained roots of Salix babylonica, Melaleuca quinquenervia and Casuarina cunninghamiana. These are all trees growing on creeks and river banks, in stationary or slowly flowing fresh or brackish waters in swamps, creeks, drains and channels, and in seepage areas of New South Wales, Australia. Larger and older roots lacked VAM infection in the inner cortex, probably due to suberisation of cells, and the endophyte was restricted to the epidermal layers. Spores and sporocarps of the VAM fungi Glomus fasciculatus, G. mosseae, Sclerocystis rubiformis, Gigaspora margarita and an unidentified Scutellospora sp. were wet sieved and decanted from aquatic sediments and soils. The presence of similar VAM fungal spores in the aquatic sediments and terrestrial soil suggests that they probably enter the aquatic sediments through run off from the land ecosystem. All three plants formed vesicular arbuscular (VA) mycorrhizae almost exclusively in the marshy, periodically inundated soils, but the same plant species formed endo-/ ectomycorrhizae when growing in soil with higher redox potentials (E _h). Salix and Melaleuca tree roots possessed both VAmycorrhizae and ectomycorrhizae. VAM roots of Casuarina were equipped with both N-fixing Frankia nodules and proteoid roots. VAM endophytes did not invade nodular cortical tissues, suggesting the presence of an exclusion mechanism which needs further study. The highest VAM infection was found in nodulated specimens. Free-floating roots growing in water close to the banks were non-mycorrhizal but were mycorrhizal in the bottom-rooting state. VAM spore number and mycorrhizal infection seem to be associated with redox-potential, i.e. lower at sites such as swamps, water or sediments with lower E _h values than in terrestrial soils with higher E _h values. A relationship between soil moisture gradient and VAM infection pattern became apparent from the study of a C. cunninghamiana transect on a creek embankment, i.e. typical vesicles and arbuscules were found in roots from drier soils, there was a lack of arbuscules in relatively wet soils but large lipid-filled intracellular vesicles were present, and typical vesicles and arbuscules were absent in flooded creek beds where roots were associated with coenocytic intercellular hyphae with abundant lipid droplets. The importance of VA mycorrhiza, ectomycorrhizae, N-fixing root nodules and proteoid roots at the land-water interface is discussed with reference to the use of these trees as pioneering species for stabilising river and stream banks, reducing erosion, windbreaking, and as a long-term and inexpensive means of achieving biological control of aquatic weeds by shading waterways.     

Transpiration of detached leaves from mycorrhizal and nonmycorrhizal cowpea and rose plants given varying abscisic acid, pH, calcium, and phosphorus

 Vesicular-arbuscular mycorrhizal (VAM) colonization can alter transpiration of host leaves, but scientists remain unclear about the mechanisms involved. We tested whether intact root systems were required to observe effects of root colonization by Glomus intraradices on leaf transpiration, or whether some VAM influence resided in leaves even after they were detached from root systems. We measured the transpiration of detached leaves of VAM and nonmycorrhizal plants exposed to different levels of several substances known to influence stomata locally or act in whole-plant regulation of transpiration: abscisic acid, calcium, phosphorus, and hydrogen ions. In rose, some VAM influence on transpiration resided in leaves, even after they had been separated from their root systems. However, removing leaves from their root systems eliminated the VAM influence on stomatal behavior of cowpeas. Accepted: 22 June 1998     

A tripartite culture system for endomycorrhizal inoculation of micropropagated strawberry plantlets in vitro

The objective of the current investigation was to develop a reliable method to obtain vesicular arbuscular mycorrhizae (VAM) in micropropagated plantlets and to determine their influence on growth. An in vitro system for culturing the VA mycorrhizal fungus Glomus intraradices with Ri T-DNA-transformed carrot roots or nontransformed tomato roots was used in this study as a potential active source of inoculum for the colonization of micropropagated plantlets. After root induction, micropropagated plantlets grown on cellulose plugs (sorbarod) were placed in contact with the primary mycorrhizae in growth chambers enriched with 5000 ppm CO₂ and fed with a minimal medium. After 20 days of tripartite culture, all plantlets placed in contact with the primary symbiosis were colonized by the VAM fungus. As inoculum source, 30-day-old VA mycorrhizal transformed carrot roots had a substantially higher infection potential than 5-, 10-or 20-day-old VAM. Colonized plantlets had more extensive root systems and better shoot growth than control plants. The VAM symbiosis reduced the plantlet osmotic potential. This response may be a useful pre-adaptation for plantlets during transfer to the acclimatization stage.