Branched absorbing structures (BAS): a feature of the extraradical mycelium of symbiotic arbuscular mycorrhizal fungi

Abstract

The present work describes the morphogenesis and cytological characteristics of ' branched absorbing structures ' (BAS, formely named arbuscule-like structures, ALS), small groups of dichotomous hyphae formed by the extraradical mycelium of arbuscular mycorrhizal (AM) fungi. Monoxenic cultures of the AM fungus Glomus intraradices Smith & Schenck and tomato (Lycopersicum esculentum Mill.) roots allowed the continuous, nondestructive study of BAS development. These structures were not observed in axenic cultures of the fungus under different nutritional conditions or in unsuccessful (asymbiotic) monoxenic cultures. However, extraradical mycelium of G. intraradices formed BAS immediately after fungal penetration of the host root and establishment of the symbiosis. The average BAS development time was 7 d under our culture conditions, after which they degenerated, becoming empty septate structures. Certain BAS were closely associated with spore formation, appearing at the spore's substending hypha. Branches of these spore-associated BAS (spore-BAS) usually formed spores. Electron microscopy studies revealed that BAS and arbuscules show several ultrastructural similarities. The possible role of BAS in nutrient uptake by the mycorrhizal plant is discussed.

Efeito de fungos micorrízicos arbusculares, da adubação fosfatada e da esterilização do solo no crescimento de mudas de maracujazeiro amarelo

“…Fungos micorrízicos arbusculares (FMA) podem constituir outra alternativa para incrementar a produção de mudas, reduzindo a necessidade de aplicação desses insumos, sobretudo considerando a dependência do maracujazeiro à micorrização . Expandindo a zona de absorção da raiz, pelo desenvolvimento de hifas que se ramificam, explorando e absorvendo maior quantidade de nutrientes minerais do solo, os FMAs podem acarretar maior crescimento das plantas, em menos tempo (Bago et al, 1998). Além da melhoria na nutrição, a inoculação com FMA tem sido responsável pelo melhor estabelecimento de mudas no transplantio para o campo, conferindo também maior tolerância a patógenos do solo (Smith & Read, 1997).…”

Distribution of the arbuscular mycorrhizal biomarker C16:1cis11 among neutral, glyco and phospholipids extracted from soil during the reproductive growth of corn

“…One explanation may be that as the crop matures a reduction in C supply to AM fungi between R5 and R6 stage of corn may trigger the production of glycolipids in spore-related structures formed by symbiotic fungi. Bago et al (1998) observed in Glomus intraradices that arbuscules develop along intraradical, intercellular hyphae or intracellular coils, while branched absorbing structures (BAS) are formed on extraradical mycelia, possibly associated with spore formation. Arbuscules and BAS share several cytological characteristics: both contain numerous nuclei, mitochondria, glycogen deposits, lipid globules, abundant polyvesicular bodies and electrodense granules inside small vacuoles (Bonfante-Fasolo, 1984;Bago et al, 1998).…”

“…Bago et al (1998) observed in Glomus intraradices that arbuscules develop along intraradical, intercellular hyphae or intracellular coils, while branched absorbing structures (BAS) are formed on extraradical mycelia, possibly associated with spore formation. Arbuscules and BAS share several cytological characteristics: both contain numerous nuclei, mitochondria, glycogen deposits, lipid globules, abundant polyvesicular bodies and electrodense granules inside small vacuoles (Bonfante-Fasolo, 1984;Bago et al, 1998). In plants, steryl glucosides and their acylated derivatives (GLFA) are located in microsomal and mitochondria membranes (Harwood, 1977).…”

In vitro culture of arbuscular mycorrhizal fungi: advances and future prospects

“…Development of extraradical mycelium under aseptic conditions is often accompanied by the production of so-called arbuscule-like structures (ALS) (Bago et al, 1998a) or branched absorbing structures (BAS) (Bago et al, 1998b). The authors suggest the possible implication of the ALS/BAS in the exchange sites between AM fungi and host plants.…”