Adriana Parada Dias da Silveira

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.

Cadmium Accumulation in Sunflower Plants Influenced by Arbuscular Mycorrhiza

In order to investigate the cadmium (Cd) accumulation patterns and possible alleviation of Cd stress by mycorrhization, sunflower plants (Helianthus annuus L.) were grown in the presence or absence of Cd (20 μmol L−1) and inoculated or not inoculated with the arbuscular mycorrhizal fungus (AMF) Glomus intraradices. No visual symptoms of Cd phytotoxicity were observed; nevertheless, in non-mycorrhizal plants the presence of Cd decreased plant growth. The addition of Cd had no significant effect on either mycorrhizal colonization or the amount of extra-radical mycelia that was produced by the AMF. Cd accumulated mainly in roots; only 22% of the total Cd absorbed was translocated to the shoots, where it accumulated to an average of 228 mg Cd kg−1. Although the shoot-to-root ratio of Cd was similar in both the AMF inoculated and non-inoculated plants, the total absorbed Cd was 23% higher in mycorrhizal plants. Cd concentration in AMF extra-radical mycelium was 728 μg g−1 dry weight. Despite the greater absorption of Cd, mycorrhizal plants showed higher photosynthetic pigment concentrations and shoot P contents. Cd also influenced mineral nutrition, leading to decreased Ca and Cu shoot concentrations; N, Fe and Cu shoot contents; and increased S and K shoot concentrations. Cd induced guaiacol peroxidase activity in roots in both mycorrhizal and non-mycorrhizal plants, but this increase was much more accentuated in non-mycorrhizal roots. In conclusion, sunflower plants associated with G. intraradices were less sensitive to Cd stress than non-mycorrhizal plants. Mycorrhizal sunflowers showed enhanced Cd accumulation and some tolerance to excessive Cd concentrations in plant tissues.

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.

Cadmium effect on the association of jackbean (Canavalia ensiformis) and arbuscular mycorrhizal fungi

O efeito do cadmio na associacao micorrizica e no teor e acumulo de Cd na raiz e parte aerea de feijao de porco foi avaliado em condicao de hidroponia. Os tratamentos consistiram da inoculacao ou nao de tres especies de fungos micorrizicos arbusculares (FMAs), Glomus etunicatum, G. intraradices e G. macrocarpum, e uma testemunha (ausencia de FMA), duas concentracoes de Cd ( 0 e 5 µmol L-1) e de P (1 e 10 mg L-1) na solucao nutritiva. Foram determinados a colonizacao micorrizica, o comprimento do micelio extraradical, atividade da peroxidase nas raizes, crescimento das plantas e teor e acumulo de Cd e P na raiz e na parte aerea das plantas. A associacao micorrizica nao promoveu crescimento das plantas mas aumentou a concentracao foliar e radicular de Cd. O metal pesado foi acumulado principalmente nas raizes e somente uma pequena quantidade foi translocada para a parte aerea. A colonizacao micorrizica nao foi influenciada pelo Cd adicionado, mas o micelio extrarradicular mostrou-se sensivel ao metal, tendo sido reduzido em 25%, principalmente na menor concentracao de P adicionado. Nesta mesma concentracao de P, a adicao de Cd reduziu a atividade da peroxidase nas raizes das plantas nao colonizadas e nas colonizadas por G. macrocarpum. Entretanto, as raizes micorrizadas mostraram valores menores de atividade da enzima. Melhor desempenho da associacao micorrizica foi constatado nas plantas colonizadas por G. etunicatum, o qual mostrou-se promissor na fitorremediacao de solos contaminados por Cd quando em associacao ao feijao de porco.

Arbuscular mycorrhiza and kinetic parameters of phosphorus absorption by bean plants

The mechanisms that determine greater P absorption by mycorrhizal plants are still not completely clear, and are attributed, in part, to an increase in the number of absorption sites promoted by the hyphae, and/or to a greater affinity of the colonized hypha or root carriers to P. The effect of mycorrhizae formed by Glomus etunicatum on the kinetic parameters of P absorption by the roots and on P influx in bean plants of the IAC-Carioca cultivar was evaluated, in two distinct plant development periods: at the onset of flowering and at the pod-filling stage (35 and 50 days after sowing, respectively). A mixture of sand and silica (9:1) was utilized as substrate and irrigated with nutrient solution. The kinetics assay was performed by the method of 32P depletion from the solution (depletion curve), using intact plants. Mycorrhization promoted greater growth and P absorption by bean plants, which was more conspicuously observed at the pod-filling stage. Mycorrhizal plants showed higher values of maximum ion uptake rate (Vmax) and net P influx at the flowering stage. Lower minimum ion concentration (Cmin) and Michaelis-Menten constant (Km) values were verified in mycorrhizal plants at the pod-filling stage. Mycorrhizal plants also presented higher net P influx per plant, in both stages. Cmin was the kinetic parameter more intimately related to P absorption, and a significant correlation was obtained between this parameter and shoot P content and accumulation in bean plants.

Chemical and microbiological attributes of an oxisol treated with successive applications of sewage sludge

Studies on sewage sludge (SS) have confirmed the possibilities of using this waste as fertilizer and/or soil conditioner in crop production areas. Despite restrictions with regard to the levels of potentially toxic elements (PTE) and pathogens, it is believed that properly treated SS with low PTE levels, applied to soil at adequate rates, may improve the soil chemical and microbiological properties. This study consisted of a long-term field experiment conducted on a Typic Haplorthox (eutroferric Red Latosol) treated with SS for seven successive years for maize production, to evaluate changes in the soil chemical and microbiological properties. The treatments consisted of two SS rates (single and double dose of the crop N requirement) and a mineral fertilizer treatment. Soil was sampled in the 0-0.20 m layer and analyzed for chemical properties (organic C, pH, P, K, Ca, Mg, CEC, B, Cu, Fe, Mn, Zn, Cd, Ni, and Pb) and microbiological properties (basal respiration, microbial biomass activity, microbial biomass C, metabolic quotient, microbial quotient, and protease and dehydrogenase enzyme activities). Successive SS applications to soil increased the macro- and micronutrient availability, but the highest SS dose reduced the soil pH significantly, indicating a need for periodic corrections. The SS treatments also affected soil microbial activity and biomass negatively. There were no significant differences among treatments for maize grain yield. After seven annual applications of the recommended sludge rate, the heavy metal levels in the soil had not reached toxic levels.

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,

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.

Endophytic bacteria affect sugarcane physiology without changing plant growth

The aim of this study was to evaluate if endophytic bacteria inoculants would be beneficial to the sugarcane varieties IACSP94-2094 and IACSP95-5000, promoting changes in photosynthesis and plant growth. The plants, obtained from mini stalks with one bud, were treated with two bacteria mixtures (inoculum I or II) or did not receive any inoculum (control plants). The inocula did not affect shoot and root dry matter accumulation as compared to the control condition (plants with native endophytic bacteria). However, photosynthesis and electron transport rate (ETR) increased in IACSP94-2094 treated with the inoculum II, whereas the inoculum I enhanced photosynthesis and stomatal conductance in IACSP95-5000. The inoculum II caused increase in leaf sucrose concentration of IACSP94-2094 and decrease in IACSP95-5000 leaves. Leaf nitrogen concentration was not affected by treatments, but bacteria inoculation increased nitrate reductase activity in IACSP95-5000, and the highest activity was found in plants treated with the inoculum II. We can conclude that bacteria inoculation changed sugarcane physiology, improving photosynthesis and nitrate reduction in a genotype-dependent manner, without promoting plant growth under non-limiting conditions.