Fungi Symbiosis ( Read ) | Biology | CK Foundation
Lichens are quite a large group of organisms. Fungi constitute one of the five kingdoms of living organisms and of all fungi about 20 per cent are lichens. The basis of the mutualistic symbiosis in lichens is similar to the mycorrhizal partnership between some species of fungi and the roots of most plants. The lichen. The tiny lichen is a critical part of the food chain, but how do algae and fungi work together to form these symbiotic organisms?.
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. 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. 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.
Lichens : Symbiotic Relation Between Algae and Fungi
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. 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. When the tide comes in they are released into the water. The sperm, released in numbers large enough to colour the water orange, swim activly in search of eggs and attach to them when they find one.
Eggs can be observed spinning wildly, powered by hundreds of sperm attached to their surface. Finally one sperm succeeds in fertilizing the egg, which then sinks to the bottom to grow into a new plant. In the fungus, the hyphae contains two mating strains, called plus and minus strains because there are no anatomical distinctions between them. The nuclei from these two mating strains fuse within a special, multicellular reproductive structure on the surface of the lichen.
The fused nuclei divide several times and produce spores, which are carried away by the wind and may germinate to form a new mass of hyphae. These new fungal hyphae are free of algae and typically must link with an alga in order to survive. The algal cells within the lichen reproduce through mitosis, a process in which a single cell divides into two genetically identical cells. Lichens as a unit may also undergo asexual reproduction. The lichen may slough off small clumps of soredia, intertwined fungal hyphae with a few algal cells, which disperse to new habitats.
Alternatively, the lichen may produce small, fingerlike buds on the surface called isidia, which break off and form new lichens. IV Importance of Lichens Lichens are common food for insects and slugs. In the arctic tundra, reindeer and caribou rely on lichens during the winter, when no other food is available.
Several species of lichens that sprout up through the snow are called reindeer mosses. Humans rarely eat lichens except in cases where no other food is available. The Bible may chronicle one such example: Some scholars believe that the manna or bread that the ancient Israelites ate in the desert when they fled Egypt was made of lichen.
In Japan, where algae as well as fungi are prized foods, certain lichens are eaten as delicacies. Although lichens have been used in folk medicine as purported cures for many ills, from headaches and toothaches to tuberculosis, diabetes, and asthma, their use in modern medicine is recent. The discovery in the s that some fungi produce potent antibiotics stimulated an extensive screening of fungi and lichens. Since then, lichen extracts have found limited use in Europe, where lichen antibiotics have been used to treat tuberculosis and some skin diseases.
Lichen extracts are also used to add color or scent. Many lichens have earthy red, brown, russet, and blue pigments, and these pigments have been used as clothing dyes since the time of ancient Greece. Native Americans use boiled lichen extracts to dye cloth and baskets.
Symbiosis in lichens - Wikipedia
Even the famous Harris tweeds, woolen textiles from the Scottish islands, are still dyed with Scottish lichens. A number of dark, oily extracts from European and African lichens are used to add scents to soaps and perfumes. Lichens are used as living indicators of environmental problems because of their sensitivity to atmospheric pollution.