Lichens | Herbarium | USU
Hello, In lichens (blue-green algae) the algae benefit their fungal partner by producing What is the relevant symbiotic relationship between algae and fungi ?. A mycorrhiza is a mutualistic relationship between a fungus and a plant. roots) and lichen (fungi and either cyanobacteria or green algae). The tiny lichen is a critical part of the food chain, but how do algae and fungi work together to form these symbiotic organisms?.
Symbiosis in lichens - Wikipedia
The thalli produced by a given fungal symbiont with its differing partners will be similar, and the secondary metabolites identical, indicating that the fungus has the dominant role in determining the morphology of the lichen. Further, the same algal species can occur in association with different fungal partners. Lichens are known in which there is one fungus associated with two or even three algal species. Rarely, the reverse can occur, and two or more fungal species can interact to form the same lichen.
Chlorococcales is now a relatively small order and may no longer include any lichen photobionts. Algae that resemble members of the Trebouxia are presumed to be in the class Trebouxiophyceae and go by the same descriptive name Trebouxioid. Cyanolichens[ edit ] Although the photobionts are almost always green algae chlorophytasometimes the lichen contains a blue-green alga instead cyanobacterianot really an algaand sometimes both types of photobionts are found in the same lichen.
A cyanolichen is a lichen with a cyanobacterium as its main photosynthetic component photobiont. The picture at right depicts yet another species of Verrucaria mucosa, a close relative of H. In fact, it releases its ascospores when it is above the water and thus depends upon being exposed to air.
However, it does not grow in the upper areas of the tide like H. In the picture V. On parts of the rock that have dried it is harder to see but you may notice that it is slightly green, revealing the presence of the photobiont. The red spots are the alga Hildenbrandia polytypa, similar is size and growth habit to V.
The last picture again shows Verrucaria mucosa, this time growing under water at high tide. Note that even this lichen has its limits; most of the rocks in the picture have no lichens at all. This may be because the rocks are too small and may be moved by currents as the tide ebbs and flows or it may be that their surfaces are unsuitable for lichens.
Another problem that lichens face is being eaten by animals. Many contain acids and other compounds that make them unpalatable to animals but V. Notice the large rock above the one with lichens on it.
On its surface is a small snail called a periwinkle. Some periwinkles, notably the rough periwinkle, eat V. This has not happened here yet but there are in fact several periwinkles present, as well as the white barnacles and a mussel. How many periwinkles are here?
Not many at first glance, but you might be surprised. Click on the picture to get an enlarged view and see how many periwinkles you can count.
One of the more intriguing mutualisms found in our region is the one between the brown alga Ascophyllum nodosum and the fungus Mycophycias ascophylli.
MUTUALISMS BETWEEN FUNGI AND ALGAE
Ascophyllum nodosum, commonly called rockweed, occurs in the intertidal zone where it is left exposed to the air when the tide goes out. Mycophycias ascophylli, a member of the lichen-forming order of fungi Verrucarialesgrows within the body thallus of A. In return the fungus has access to carbohydrates and other nutrients within its protective environment. Garbary and colleagues at St.
Francis Xavier University in Nova Scotia have studied this mutualism in detail and have shown that the fungus not only forms relationships with the rockweed but also seems to form a mutualism with Polysiphonia lanosa, a common epiphyte found attached to the A. At far left is a thallus of A. You may wish to look further back on this page to see the habitat photo of A.
The next picture shows a detail from the first panel. The small almond-shaped structures along the stem are receptacles. Each receptacle bears a number of conceptacles, structures that release sperm and egg into the ocean each spring. These are seen as bumpy areas in the second photo but in the third more highly magnified panel they can be seen more easily and reveal the pores through which the sperm and egg escape.
The next panel is even further magnified and the conceptacles are even clearer. In this panel it is also possible to see tiny black dots, resembling grains of pepper; these are the perithecia fruiting bodies of Mycophycias ascophylli. The blue box drawn on around one of these leads to the next photograph, taken with a compound microscope, showing a detailed view of one perithecium partially submerged in the receptacle.
The perithecia contain asci and ascospores. The last panel shows one ascus containing eight 2-celled ascospores.
Fungi Symbiosis ( Read ) | Biology | CK Foundation
The ascospores are not very clear in this picture but are nevertheless nearly mature. In our region Ascophyllum nodosum releases its sperm and eggs in late May. On a warm day at low tide these tiny cells ooze out of the conceptacles like toothpaste out of a tube.
Evidence that lichens are examples of successful symbiosis is the fact that lichens can be found in almost every habitat and geographic area on the planet. There is evidence to suggest that the lichen symbiosis is parasitic or commensalisticrather than mutualistic.
Photobiont cells are routinely destroyed in the course of nutrient exchange. The association is able to continue because reproduction of the photobiont cells matches the rate at which they are destroyed.
In many species the fungus penetrates the algal cell wall,  forming penetration pegs haustoria similar to those produced by pathogenic fungi that feed on a host. Miniature ecosystem and holobiont theory[ edit ] Symbiosis in lichens is so well-balanced that lichens have been considered to be relatively self-contained miniature ecosystems in and of themselves.
Lichens have been used in making dyesperfumes and in traditional medicines. A few lichen species are eaten by insects  or larger animals, such as reindeer.
If air is very badly polluted with sulphur dioxide there may be no lichens present, just green algae may be found. If the air is clean, shrubby, hairy and leafy lichens become abundant. A few lichen species can tolerate quite high levels of pollution and are commonly found on pavements, walls and tree bark in urban areas.
Symbiosis in lichens
The most sensitive lichens are shrubby and leafy while the most tolerant lichens are all crusty in appearance.
Since industrialisation many of the shrubby and leafy lichens such as Ramalina, Usnea and Lobaria species have very limited ranges, often being confined to the parts with the purest air. Lichenicolous fungi[ edit ] Some fungi can only be found living on lichens as obligate parasites.
These are referred to as lichenicolous fungiand are a different species from the fungus living inside the lichen; thus they are not considered to be part of the lichen. When the cortex is more transparent, the algae show more clearly and the lichen looks greener. Metabolites, metabolite structures and bioactivity[ edit ] Lichens can show intense antioxidant activity.
Life span[ edit ] Lichens may be long-livedwith some considered to be among the oldest living organisms. In an experiment led by Leopoldo Sancho from the Complutense University of Madrid, two species of lichen— Rhizocarpon geographicum and Xanthoria elegans —were sealed in a capsule and launched on a Russian Soyuz rocket 31 May Once in orbit, the capsules were opened and the lichens were directly exposed to the vacuum of space with its widely fluctuating temperatures and cosmic radiation.