Symbiosis in lichens - Wikipedia
Carlos Vicente, Team of Cellular Interactions in Plant. Symbiosis the first description of lichen as an alga - fungus association, it was known. cross section of lichen, a symbiosis between green algae and a fungus. 1. Thick layers of hyphae, called the cortex 2. Green algae 3. Loosely packed hyphae 4. Anchoring hyphae called rhizines. Symbiosis in lichens is the mutually helpful symbiotic relationship of green algae and/or nonlichenized fungi that live as saprotrophs or plant parasites (for example. This paper addresses the hypothesis that land plants have a biphyletic origin as the product of an endocellular mutualism between a green alga and a.
Lichenized and nonlichenized fungi can even be found in the same genus or species. TrebouxiophyceaePhaeophyceaeChlorophyceae have been found to associate with the lichen-forming fungi.
One fungus, for example, can form lichens with a variety of different algae. 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.
MUTUALISMS BETWEEN FUNGI AND ALGAE
Another cyanolichen group, the jelly lichens e. They are nearly as easy to find and study in the middle of winter as during the warmer months. The first of the three photographs above was taken in Saskatchewan, out in an open prairie. The rock in the forground is the highest point in the immediate area; animals sitting there get a panoramic view of the grassland and all that is taking place there. It is a favourite place for birds, especially birds of prey waiting for a mouse or vole that might be moving through the grass.
The orange lichen is a species of Xanthoria that thrives on nitrogen-rich bird droppings left on the rock. Similar species of Xanthoria, as well as members of the related genus Caloplaca, can be found on our seacoast on rocks frequented by gulls and cormorants. The second of the two pictures above is of White Horse Island, a small island in the Bay of Fundy supporting large colonies of nesting birds.
The white colour of the rock is due to a thick layer of bird droppings; the orange material is a species of Caloplaca. The gravestone at left marks the resting place of Roland ThaxterProfessor at Harvard University and brilliant mycologist, known in particular for his monumental studies on the Laboulbeniales. Beside Roland's grave is that of his brother Karl. Both gravestones have become colonized by lichens and are now difficult to read.
Click on the photograph to get an enlarged version of Roland's gravestone Another interesting thing about our coastal lichens is that some of them are highly tolerant of salt, a substance that is toxic to most fungi, including lichenized ones.
The picture at right depicts some coastal rocks on the Bay of Fundy near Saint John. At the bottom of the picture are bunches of brown algae, mostly Fucus vesiculosus and Ascophyllum nodosum, commonly called rockweed. These rockweeds grow in areas along the shore where they will be immersed in seawater, at least at high tide. At the very top of the rock is a patch of orange, probably Xanthoria parietina. In between is a black zone consisting of the custose lichen Hydropunctaria maura.
Hydropunctaria maura can grow where it is periodically immersed in seawater but is also able to grow in an area just above that where it receives only splash from waves. This "black zone" occupies an area that often goes for days or even weeks without immersion in seawater but will eventually get splashed. This is a tough place to live: Just the place for a lichen! 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.
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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?
Symbiosis in lichens
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. 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.
Mutualisms between fungi and algae
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. The ascospores are not very clear in this picture but are nevertheless nearly mature.