Mycelium

About: Mycelium is a research topic. Over the lifetime, 8923 publications have been published within this topic receiving 170993 citations.

Extraradical mycelium of the arbuscular mycorrhizal fungus Glomus lamellosum can take up, accumulate and translocate radiocaesium under root-organ culture conditions.

Abstract: Radiocaesium enters the food chain when plants absorb it from soil, in a process that is strongly dependent on soil properties and plant and microbial species. Among the microbial species, arbuscular mycorrhizal (AM) fungi are obligate symbionts that colonize the root cortex of many plants and develop an extraradical mycelial (ERM) network that ramifies in the soil. Despite the well-known involvement of this ERM network in mineral nutrition and uptake of some heavy metals, only limited data are available on its role in radiocaesium transport in plants. We used root-organ culture to demonstrate that the ERM of the AM fungus Glomus lamellosum can take up, possibly accumulate and unambiguously translocate radiocaesium from a 137Cs-labelled synthetic root-free compartment to a root compartment and within the roots. The accumulation of 137Cs by hyphae in the root-free compartment may be explained by sequestration in the hyphae or by a bottleneck effect resulting from a limited number of hyphae crossing the partition between the two compartments. Uptake and translocation resulted from the incorporation of 137Cs into the fungal hyphae, as no 137Cs was detected in mycorrhizal roots treated with formaldehyde. The importance of the translocation process was indicated by the correlation between 137Cs measured in the roots and the total hyphal length connecting the roots with the labelled compartment. 137Cs may be translocated via a tubular vacuolar system or by cytoplasmic streaming per se.

Spore germination, homing reaction, and intersterility groups in laccaria laccata (agaricales)

Abstract: Spore germination was induced in 29 of 30 collections from different basidiocarps of Laccaria laccata by placing the spores on a charcoal-dusted agar medium containing 0.2% peptone, on the surface of which a mycelium of L. laccata was growing. Preserved at 4 C the spores maintained their viability for 2 to 3 months; at -18 C they were viable for about 4 months. Growing hyphae of L. laccata showed a typical homing response towards germinating spores, the eventual conjunction between the hyphal tip cell and the spore leading either to a lethal or to a non-lethal reaction. Mating tests with single-spore mycelia from different stocks, i.e., from spores derived from different basidiocarps, showed that the 14 tested stocks represented four intersterile groups. A method inducing basidiospore germination of Laccaria laccata (Scop.: Fr.) Bk. & Br. under controlled conditions has been described (Fries, 1977). The method was based on two principles: the removal, by means of activated charcoal, of inhibitory substances in the agar medium, and the introduction of a germination-inducing colony of Rhodotorula glutinis (Fres.) Harrison among the spores placed on that medium. However, when the method was tested on a large number of spore collections of L. laccata s.lat. germination was in most cases poor or absent. This implied an unfortunate limitation of the possibilities to obtain monosporous isolates from different strains of this fungus for physiological and genetic investigations. Since L. laccata in many respects is more suitable than most other mycorrhizal fungi for in vitro studies, renewed experiments seemed justified to improve the germination-inducing method. The results of these experiments are reported in the present paper. Recognition reactions in this fungus similar to those earlier described for several species of Leccinum (Boletales) (Fries, 1981) were also discovered. Since spore germination permitted isolation of monosporous mycelia some observations could also be made on incompatibility patterns in L. laccata.

Interactions between the biocontrol agent Pseudomonas fluorescens CHA0 and Thielaviopsis basicola in tobacco roots observed by immunofluorescence microscopy

Abstract: Pseudomonas fluorescens CHA0 protects plants from damage caused by several soilborne fungi. In this work, immunofluorescence microscopy was used to investigate the colonization of tobacco roots by CHA0 and its physical relationship with the black root rot fungus Thielaviopsis basicola. The pseudomonad colonized the rhizoplane shortly after planting of tobacco seedlings in sterile soil microcosms, in which it had been introduced as soil inoculant. CHA0 was found between and inside cells in the epidermis and the cortex, as well as in the xylem vessels, within 4–7 days after planting of seedlings. The presence of CHA0 delayed the colonization of the interior of tobacco roots by T. basicola compared with the treatment in which only the fungus had been inoculated. Likewise, the pseudomonad reduced the extent of black root rot from 82% to 28%. However, CHA0 was seldom found in contact with the mycelium of T. basicola or in its vicinity, indicating that direct colonization of the mycelium of T. basicola by CHA0 was not required for protection of tobacco against black root rot. Overall, the results suggest that the interior of the root is a key site for implementation of the strain’s biocontrol activity against soilborne plant-pathogenic fungi.

Hydrolytic enzymes and ability of arbuscular mycorrhizal fungi to colonize roots.

Abstract: biology, ecological specificity and symbiotic activity (Giovannetti and Gianinazzi-Pearson, 1994) There are The production of hydrolytic enzymes from external many reports of inter- and intraspecific differences in the mycelia associated with roots and colonized soybean efficiency of AM fungi in terms of plant growth and roots (Glycine max L) inoculated with different arbus- protection (Harley and Smith, 1983; Sieverding, 1991; cular-mycorrhizal (AM) fungi of the genus Glomus, and Ruiz-Lozano and Azcon, 1995; Ruiz-Lozano et al, 1995) the possible relationship between these activities and The physiological basis for these variations is poorly the capacity of the AM fungi to colonize plant roots known The ability of mycorrhizas to increase plant was studied There were differences in root coloniza- growth can in most cases be explained by an increased tion and plant growth between the Glomus strains, phosphorus uptake The hyphal spread of AM fungi is and also between two isolates of G mosseae an important factor influencing the phosphorus supply to Hydrolytic activities in the root and external mycelia the host plant (Jakobsen et al, 1992) Mycorrhizal fungi associated with roots differed in the AM fungi tested may differ in their capacity to develop an external hyphal Correlations were only found between the endoxylog- system regardless of their capacity to colonize the root lucanase activity of the external mycelia associated cortex (Graham et al, 1982) The morphological proper- with roots of the AM fungi tested and the percentage ties and spatial distribution of the external hyphae in soil root colonization or plant growth However, hydrolytic and differences in hyphal uptake, translocation capacities activities of roots colonized by the different endo- and metabolic activity seem to play an important role in phytes correlated with those of external mycelia The the efficiency of AM fungi ( Kothari et al, 1991; Jakobsen hydrolytic activities were not qualitatively different et al, 1992) because the endoxyloglucanase from AM colonized Differences in the ability of mycorrhizal fungi to roots and the external mycelia did not show a high enhance phosphorus uptake and growth of the host plant, degree of polymorphism in the different species of even between species for which the extent of root coloniza- fungus tested The possible role of the hydrolytic activ- tion is similar, may be due to functional differences in ity of external hyphae of AM fungi was discussed as a the host-fungal interface Different band patterns of factor affecting fungal ability to colonize the root and enzymatic activities in AM fungi belonging to the same influence plant growth