Sara Adrián López de Andrade

Zn uptake, physiological response and stress attenuation in mycorrhizal jack bean growing in soil with increasing Zn concentrations

The influence of arbuscular mycorrhizal fungi (AMF) inoculation on Canavalia ensiformis growth, nutrient and Zn uptake, and on some physiological parameters in response to increasing soil Zn concentrations was studied. Treatments were applied in seven replicates in a 2 x 4 factorial design, consisting of the inoculation or not with the AMF Glomus etunicatum, and the addition of Zn to soil at the concentrations of 0, 100, 300 and 900 mg kg(-1). AMF inoculation enhanced the accumulation of Zn in tissues and promoted biomass yields and root nodulation. Mycorrhizal plants exhibited relative tolerance to Zn up to 300 mg kg(-1) without exhibiting visual symptoms of toxicity, in contrast to non-mycorrhizal plants which exhibited a significant growth reduction at the same soil Zn concentration. The highest concentration of Zn added to soil was highly toxic to the plants. Leaves of plants grown in high Zn concentration exhibited a Zn-induced proline accumulation and also an increase in soluble amino acid contents; however proline contents were lower in mycorrhizal jack beans. Plants in association or not with the AMF exhibited marked differences in the foliar soluble amino acid profile and composition in response to Zn addition to soil. In general, Zn induced oxidative stress which could be verified by increased lipid peroxidation rates and changes in catalase, ascorbate peroxidase, glutathione reductase and superoxide dismutase activities. In summary, G. etunicatum was able to maintain an efficient symbiosis with jack bean plants in moderately contaminated Zn-soils, improving plant performance under those conditions, which is likely to be due to a combination of physiological and nutritional changes caused by the intimate relation between fungus and plant. The enhanced Zn uptake by AMF inoculated jack bean plants might be of interest for phytoremediation purposes.

Lead tolerance and phytoremediation potential of Brazilian leguminous tree species at the seedling stage.

A greenhouse pot experiment was conducted to evaluate the potential of three Brazilian leguminous woody species, Mimosa caesalpiniaefolia, Erythrina speciosa and Schizolobium parahyba, for the revegetation of lead- (Pb-) contaminated areas. The response of seedlings to increasing Pb concentrations (0, 250, 500 and 1000 mg kg(-1)) in the soil was studied. In addition to Pb accumulation and translocation, the following parameters were assessed: chlorophyll, nitrate, ammonia, lipid peroxidation (MDA) and free amino acid content; seedling growth; and nitrogenase activity. No differences were observed in the germination of woody species seeds sown in soils with or without Pb addition. M. caesalpiniaefolia did not show visual symptoms of Pb toxicity, while the other two species demonstrated stress symptoms, including reduced shoot biomass yield, leaf area and height. Biochemical analyses of plant tissues revealed markedly different responses to increasing Pb concentrations, such as changes in foliar soluble amino acid composition in S. parahyba; changes in ammonia and nitrate content in E. speciosa, M. caesalpiniaefolia and S. parahyba; and changes in MDA content in S. parahyba. The levels of chlorophyll a and b and carotenoid were affected in the species studied. For the Nitrogen-fixing (N(2)-fixing) species E. speciosa, an increase of Pb in the soil affected nodule formation and growth, which led to reduced nitrogenase activity in seedlings. The concentration of Pb in shoots and roots increased with the Pb concentration in soil. However, most of the Pb absorbed accumulated in the roots, and only a small fraction was translocated to aboveground parts. These findings were confirmed by the low bioconcentration factor (BCF) and translocation factor (TF) values for the three species. The tolerance index (TI) values suggested that M. caesalpiniaefolia, a N(2)-fixing tree, was the species that was most tolerant to high Pb concentrations in soil, while E. speciosa and S. parahyba showed moderate tolerance. Of the three Brazilian native woody species studied, M. caesalpiniaefolia was found to have the highest Pb tolerance and phytostabilisation potential in Pb-contaminated soils.

Arbuscular mycorrhiza alters metal uptake and the physiological response of Coffea arabica seedlings to increasing Zn and Cu concentrations in soil

Studies on mycorrhizal symbiosis effects on metal accumulation and plant tolerance are not common in perennial crops under metal stress. The objective of this study was to evaluate the influence of mycorrhization on coffee seedlings under Cu and Zn stress. Copper (Cu) and zinc (Zn) uptake and some biochemical and physiological traits were studied in thirty-week old Coffea arabica seedlings, in response to the inoculation with arbuscular mycorrhizal fungi (AMF) and to increasing concentrations of Cu or Zn in soil. The experiments were conducted under greenhouse conditions in a 2×4 factorial design (inoculation or not with AMF and 0, 50, 150 and 450mgkg(-1) Cu or 0, 100, 300 and 900mgkg(-1) Zn). Non-mycorrhizal plants maintained a hampered and slow growth even in a soil with appropriate phosphorus (P) levels for this crop. As metal levels increased in soil, a greater proportion of the total absorbed metals were retained by roots. Foliar Cu concentrations increased only in non-mycorrhizal plants, reaching a maximum concentration of 30mgkg(-1) at the highest Cu in soil. Mycorrhization prevented the accumulation of Cu in leaves, and mycorrhizal plants showed higher Cu contents in stems, which indicated a differential Cu distribution in AMF-associated or non-associated plants. Zn distribution and concentrations in different plant organs followed a similar pattern independently of mycorrhization. In mycorrhizal plants, only the highest metal concentrations caused a reduction in biomass, leading to significant changes in some biochemical indicators, such as malondialdehyde, proline and amino acid contents in leaves and also in foliar free amino acid composition. Marked differences in these physiological traits were also found due to mycorrhization. In conclusion, AMF protected coffee seedlings against metal toxicity.

Arbuscular mycorrhizal association in coffee

Despite previous research on mycorrhizal association with plants, the data on associations with coffee ( Coffea species) are very sparse despite the great economic importance of this crop for many tropical developing countries. The present paper reviews the main aspects of the association between arbuscular mycorrhizal fungi (AMF) and coffee plants. This review includes topics on mycorrhizal effects on coffee nutritional status, pathogen–AMF interactions and responses to several environmental stresses. It also summarizes findings about the natural occurrence of AMF in different soils in which coffee is cultivated, some ecological aspects of this specific association and outlines trends for future investigations, which must elucidate the real benefits of mycorrhizae to coffee plants.

Mycorrhiza influence on maize development under Cd stress and P supply

A influencia dos fungos micorrizicos arbusculares (FMA) no acumulo e na atenuacao potencial do estresse causado pelo Cd foi estudada em plantas de milho (Zea mays L. var. Exceller). Plantas associadas ou nao com o FMA Glomus macrocarpum foram expostas ao Cd (0-20 mmol L-1) em dois niveis de P (5 e 10 mg L-1), em solucao nutritiva. O experimento foi conduzido em sistema hidroponico, com delineamento totalmente casualizado, em esquema fatorial 2 x 2 x 2. Avaliou-se o efeito da interacao micorriza-Cd sobre o crescimento da planta, o acumulo de Cd e de nutrientes, a colonizacao micorrizica da raiz e a producao de micelio extra-radical. A micorriza promoveu o crescimento da planta enquanto a adicao de Cd reduziu a producao de biomassa vegetal. Nao foram observadas diferencas nas concentracoes de Cd de plantas micorrizadas (M) e nao-micorrizadas (NM), acumulando-se o Cd principalmente nas raizes. Em geral, as raizes mostraram maior concentracao de Cd na fracao da parede celular do que na citoplasmatica, sendo que raizes de plantas M apresentaram quantidade de Cd 26% maior na fracao da parede celular do que raizes de plantas NM. As plantas M mostraram maiores relacoes P/Cd, N/Cd e S/Cd na parte aerea de que plantas NM. A colonizacao micorrizica e a quantidade de micelio extra-radical produzido pelo FMA inoculado diminuiram pela adicao de Cd, sendo a diminuicao mais pronunciada em plantas com maior suprimento de P. A adicao de Cd induziu a atividade da guaiacol peroxidase (GPOX) nas raizes; no entanto, plantas M, alem de apresentarem maiores conteudos de proteina nas raizes, nao mostraram inducao da GPOX na presenca de Cd, sugerindo maior tolerância ao metal. Conclui-se que o Cd afetou a simbiose micorrizica diminuindo a colonizacao radicular e o desenvolvimento do micelio extra-radical. No entanto, o maior crescimento e relacoes nutrientes/Cd observados em plantas M indicam uma simbiose eficiente capaz de atenuar o estresse causado pelo Cd.

Association with arbuscular mycorrhizal fungi influences alkaloid synthesis and accumulation in Catharanthus roseus and Nicotiana tabacum plants

Frequently disregarded, plant associations with arbuscular mycorrhizal fungi (AMF) can influence plant specialized metabolism with important ecological and/or economic implications. In this study, we report on both the influence of mycorrhization on the content of a wide range of alkaloids and differential gene expression of some enzymes involved in alkaloid biosynthetic pathways in the leaves and roots of Catharanthus roseus and Nicotiana tabacum plants. These plants were divided into several treatments: mycorrhizal, inoculated with AMF; non-AMF inoculated plants; and non-AMF inoculated plants with an extra supply of phosphorus. The contents of vindoline, vinblastine, vincristine, catharanthine, ajmalicine and serpentine in C. roseus and of nicotine, anabasine and nornicotine in N. tabacum tobacco plants were determined. Mycorrhizal inoculation increased ajmalicine and serpentine contents in C. roseus roots suggesting that mycorrhization had a greater influence on the accumulation of alkaloids in roots than it did in shoots. The youngest leaves of mycorrhizal C. roseus plants showed lower transcript levels of the genes analysed; however, in older leaves, the expression levels were higher when compared with the leaves of non-mycorrhizal plants. In the case of tobacco, higher leaf to root ratios for nicotine and anabasine were found in plants with a mycorrhizal association. Our results showed that mycorrhization changed the alkaloid content and expression pattern of the genes analysed in both species; however, differences were found between the roots and shoots. In nature, such changes may have a direct influence on the interactions between plants and insects (herbivory) and pathogens. These interactions must be studied further to reveal the ecological influence mycorrhizae may have on chemical defences in a broader sense.

FUNGOS MICORRÍZICOS ARBUSCULARES NA FORMAÇÃO DE MUDAS DE CAFEEIRO, EM SUBSTRATOS ORGÂNICOS COMERCIAIS ( 1 )

ARBUSCULAR MYCORRHIZAL FUNGI ON THE DEVELOPMENT OF COFFEE PLANTLETS USING DIFFERENT ORGANIC SUBSTRATES A greenhouse experiment with an alleatory factorial 9 x 4 scheme was carried out to evaluate the effects of different substrates and species of arbuscular mycorrhizal fungi (AMF) on the development of coffee plants, cultivar Catuai Amarelo, IAC 62. Nine substrates were used: seven commercial organic substrates – four substrates containing composted pinus peel (Rendmax, fertilized Vida Verde, nonfertilized Vida Verde and Terra do Paraiso), three containing coconut fiber (Golden Mix–11, Golden Mix47 and Golden Mix 80) and two using soil – a mixture of 70% soil and 30% cattle manure, usually used by the producer, and soil alone. The AMF were Glomus intraradices, Glomus etunicatum and Gigaspora margarita, and a control without AMF inoculation. The plants were harvested 200 days after transplanting and the following variables were analyzed – height, number of leaves, stem diameter, shoot dry weight,

Photosynthesis is induced in rice plants that associate with arbuscular mycorrhizal fungi and are grown under arsenate and arsenite stress

The metalloid arsenic (As) increases in agricultural soils because of anthropogenic activities and may have phytotoxic effects depending on the available concentrations. Plant performance can be improved by arbuscular mycorrhiza (AM) association under challenging conditions, such as those caused by excessive soil As levels. In this study, the influence of AM on CO2 assimilation, chlorophyll a fluorescence, SPAD-chlorophyll contents and plant growth was investigated in rice plants exposed to arsenate (AsV) or arsenite (AsIII) and inoculated or not with Rhizophagus irregularis. Under AsV and AsIII exposure, AM rice plants had greater biomass accumulation and relative chlorophyll content, increased water-use efficiency, higher carbon assimilation rate and higher stomatal conductance and transpiration rates than non-AM rice plants did. Chlorophyll a fluorescence analysis revealed significant differences in the response of AM-associated and -non-associated plants to As. Mycorrhization increased the maximum and actual quantum yields of photosystem II and the electron transport rate, maintaining higher values even under As exposure. Apart from the negative effects of AsV and AsIII on the photosynthetic rates and PSII efficiency in rice leaves, taken together, these results indicate that AM is able to sustain higher rice photosynthesis efficiency even under elevated As concentrations, especially when As is present as AsV.

Biomassa e atividade microbianas do solo sob influência de chumbo e da rizosfera da soja micorrizada

The objective of this work was to evaluate the effects of lead addition on soil microbial biomass and activity under the influence of the rhizosphere of mycorrhizal soybean. The experimental design was completely randomized and arranged in a 4x2x2 factorial scheme, using 0, 150, 300 and 600 mg dm -3 , inoculation or not of the arbuscular mycorrhizal fungus (AMF) Glomus macrocarpum and two sampling periods: soybean flowering and maturity. Microbial biomass C, soil respiration and the activity of three soil enzymes (deshydrogenase, alkaline phosphatase and arilsulphatase) were determined. The most affected enzyme was alkaline phophatase, whose activity was reduced in 60%, and which was a sensible indicator of the microbial metabolic stress caused by high Pb concentrations. Soybean mycorrhization directly influenced the rhizospheric microbiota leading to higher activity and biomass, mainly at soybean maturity stage. Soil microbiota showed stress symptoms due to Pb addition to soil.

Evaluation of Mycorrhizal Influence on the Development and Phytoremediation Potential of Canavalia Gladiata in Pb-Contaminated Soils

Soil contamination by heavy metals is a serious problem to humans due to its high level of toxicity. The heavy metal lead (Pb) is commonly used in industries and if the disposal of residues that contain this element is not done properly may result in tragic consequences to the organisms. In this experiment we assessed the potential of a forrage leguminous, Canavalia gladiata, to phytoremediate lead-contaminated soil under mycorrhizal influence. The experimental design was composed of 4 Pb doses (0, 250, 500, and 1000 mg kg−1 of soil) and the plants were inoculated or uninoculated with arbuscular mycorrhizal fungi (AMF). We observed that the nodulation was severely affected by the presence of Pb independently of the mycorrhizal status; most of the elements analyzed were affected independently of the mycorrhizal status with exception of P. The mycorrhizal colonization was able to restrict the entrance of Pb in plants under high concentrations of Pb but promoted its accumulation in both organs under intermediate concentrations of this element. Besides the mycorrhization did not promote plant growth under Pb stress, the use of this plant may be considered to be used for phytostabilization purposes.