Glomalina: características, produção, limitações e contribuição nos solos

Abstract

ResumoA glomalina é uma glicoproteína hidrofóbica, termoestável e recalcitrante produzida pelos fungos micorrízicos arbusculares. A glomalina é extraída das hifas ou do solo através do uso de citrato de sódio (20-50 mM; pH 7,0 ou 8,0) a elevada temperatura (121ºC), e quantificada pelos métodos Elisa ou Bradford. Acredita-se que características do solo, condições climáticas, sistema de uso do solo, práticas de manejo agrícola, presença e tipo de vegetação, dentre outros fatores, influenciam na quantidade de glomalina produzida pelos FMA. A propriedade de "cola" da glomalina auxilia a fixação das partículas do solo, favorecendo a formação de agregados estáveis. A glomalina seqüestra metais pesados, reduzindo a disponibilidade e o risco de toxicidade destes elementos para organismos e plantas crescidos em solos poluídos. Entre 28 e 45% da molécula de glomalina é constituída por carbono e de 0,9 a 7,3% é nitrogênio, chegando a representar de 4 a 5% do C e do N totais do solo. Apesar da importante contribuição da glomalina, são necessários estudos para reformulação do protocolo de extração, para identificação de sua função fisiológica para os FMA, de seus estoques em diferentes ecossistemas, dos organismos responsáveis pela sua decomposição e consumo e das espécies de FMA mais produtoras desta proteína no solo. Palavras-chave: Proteína, micorrizas, agroecossistemas AbstractGlomalin is a hydrophobic, heat-stable, and recalcitrant glycoprotein produced by arbuscular mycorrhizal fungi. The glomalin is extracted from the hyphae or from the soil through the use of sodium citrate (20-50 mM; pH 7.0 or 8.0) at high temperature (121 °C) and is quantified by ELISA or Bradford methods. Soil characteristics, climatic conditions, land use systems, agricultural practices, presence and type of vegetation, among other factors, influence the amount of glomalin produced by AMF. The 'glue' property of glomalin helps to fixate soil particles, favoring the formation of stable aggregates. Glomalin sequesters heavy metals, reducing the availability and the risk of toxicity of these elements for organisms and plants grown in polluted soils. Depending on the extraction procedure and the origin of the soil, between 28 to 45% dry weight of the glomalin molecule is carbon and 0.9 to 7.3% is nitrogen, representing up to 4 to 5% of total C and N of the soil. Despite the important contribution of glomalin, studies are needed to reformulate the extraction protocol and to identify its physiological function for the AMF, their stocks in different ecosystems, the organisms responsible for its decomposition and consumption, and the AMF species producing more of this protein in the soil.

Biological Properties and Organic Matter Dynamics of Soil in Pasture and Natural Regeneration Areas in the Atlantic Forest Biome

“…Evaluation of glomalin as a gene product in soil is inaccurate, due to limitations of the Bradford and Elisa method, which is usually used for its extraction and quantification (Whiffen et al, 2007;Sousa et al, 2012). Thus, glomalin has been operationally assessed as a glomalin-related soil protein (GRSP) (Rillig, 2004), considered an indicator of soil quality with good sensitivity for detecting impacts from different soil use and management systems (Silva et al, 2012b;Silva et al, in press).…”

“…In addition, they affect the physical properties of soil by mechanisms such as production of glomalin, a protein that serves as a binding agent for soil particles, promoting aggregate formation and stability (Wright et al, 1996;Morell et al, 2009). Given its role in aggregation, glomalin contributes significantly to ecosystem sustainability (Sousa et al, 2012), enhancing water infiltration, gas exchange, and root growth, decreasing erosion and increasing C storage capability (Rillig et al, 1999;Sousa et al, 2012).…”

Mycorrhizal hyphae as ecological niche for highly specialized hypersymbionts – or just soil free-riders?

“…It seems, however, that glomalin is in fact a whole group of organic compounds of unclear biological origin, some of which may well originate from the AM fungi, but then it is chewed and transformed by a number of other organisms in the soil (Gadkar and Rillig, 2006; Whiffen et al, 2007; Janos et al, 2008; Sousa et al, 2012). It is quite likely that microbes on hyphal surfaces contribute greatly to the transformations of these compounds (Bolliger et al, 2008; Gonzalez-Chavez et al, 2008), although the exact pathways and reaction rates are still unknown.…”

Comunidade de fungos micorrízicos arbusculares: diversidade, composição e glomalina em área revegetada com sesbânia

“…Essa proteína funciona no solo como um ligante orgânico (Purin, 2005) e está relacionada com a estabilidade de agregados e com o C e N do solo (Wright et al, 2007;Bedini et al, 2007;Fokom et al, 2012). De acordo com Sousa et al (2012), a quantidade de glomalina produzida pelos FMAs pode ser influenciada por diferentes fatores, como as características do solo, as condições climáticas, o sistema de uso do solo, as práticas de manejo agrícola, a presença e o tipo de vegetação.…”