Symbiotic associations

Flavonoids and other phenolic compounds released by plant roots have important functions in plant-pathogenic interactions, feeding deterrence, nematode resistance, and allelopathic interactions they also serve as signal molecules for the establishment of symbiotic associations (72,149). However, a detailed analysis of signaling pathways involved in these interactions is currently available in only a limited number of cases (see also Chap. 7). 

Baumann, P. (1998) Symbiotic associations involving microorganisms. BioScience48, 254-255. 

Table 13.1 Entomopathogenic nematodes and their symbiotically associated bacteria (Reproduced...

A mycorrhiza (literally, fungus-root) is a symbiotic association between a fungus and a plant. Mycorrhizae occur most frequently on plant roots, but may be found on any tissue involved in uptake of elements from soil. Mycorrhizae, formed by numerous fungi in the orders Phycomycetes, Basidiomycetes, and Ascomycetes, can be divided into two broad groups those that penetrate host cells (endomycorrhizae) and those that do not (ectomycorrhizae). A few fungal species defy this neat classification, penetrating the cells of one host but not those of another. 

Broers CAM, Meijers HHM, Symens JC, Stumm CK, Vogels GD, Brugerolle G (1993) Symbiotic association of Psalteriomonas vulgaris n. spec, with Methanobacterium formici-cum. Eur J Protistol 29 98-105... 

Fungi often grow in symbiotic association with other organisms. Of special importance are the mycorrhizae (fungus roots) formed by colonization of fine roots by beneficial soil fungi. Almost all plants of economic importance form mycorrihizae.104... 

Symbiotic associations of fungi with either true algae or with cyanobacteria are known as lichens. Over 15,000 varieties of lichens grow on rocks and in other dry and often cold places. While the algae appear to benefit little from the association, the fungi... 

But real systems are usually not simple feedback loops. In a virus such as bacteriophage the decision to kill the infected bacterial cell or to establish a symbiotic association with it depends on complex interactions involving a number of interconnected feedback loops. Such systems (and even simpler ones) would need a formal description in view of their complexity but as a matter of fact this complexity is such that the classical methods are much too heavy. This was a reason for trying a logical description, that is, a description using variables and functions which can take only a limited number of values—typically two (1 and 0). 

Fly Agaric and Panther Caps will grow only in "mycorrhizal relationship with just a few trees—the birch, larch, fir, pine and oak. A symbiotic association between the root cells of these trees (living or dead) and the fungus mass of underground filaments is necessary if the mushroom is to sprout. "Where these trees are not, Wasson writes, "neither does fly-agaric grow. ... 

Mycorrhizae are more widely distributed than root nodules throughout plant-microbe symbiotic systems more than 80% of terrestrial plants are able to establish mutualistic symbiotic associations with AM fungi. Hyphal branching of germinated spores of AM fungi is the crucial step for contact with plant roots. 

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