Botany online: Interactions - Plants - Fungi - Evolution - Parasitic and Symbiotic Relations
to investigate the relationship between lichen symbionts in the from the algal cell wall, fungal arginase is internalized, increasing the levels of. A lichen is a composite organism that arises from algae or cyanobacteria living among . Generally, the fungal mesh surrounds the algal or cyanobacterial cells, often . filaments (hyphae) of the fungi in a mutually beneficial symbiotic relationship. called appressoria or haustoria in contact with the wall of the algal cells. Communication between symbionts occurs before physical contact, which Relationship between fungus and alga in the lichen Cladonia cristatella Tuck. Correlation between binding patterns and cell wall cytochemistry.
The fungal partner belongs to deuteromycetes On the basis of Thallus: In this case, the thallus form crust like structure. It closely adheres to the substrate. They are found on bark or rock. Graphis, Lecanora, Haematomma In this case, thallus has leaf-like lobes.
They are fixed from the substrate by hairy rhizoids like structure called rhizines. They are attached only at central points.
There was a problem providing the content you requested
Parmellia, Collema, Peltigera Their thalli are cylindrical ribbon-like and branched. It is attached only at the base by basal mucilagenous disc. They are commonly called as shrubby lichens. Two species of Lecanora have been used as food in the barren plains and mountains of Western Asia and Northern Africa.
Lichens : Symbiotic Relation Between Algae and Fungi
Certain classes of East Siberian inhabitants use lichens as vegetable diet. It is also used for the preparation of chocolates and pastries. It is a food for reindeer and cattle. Species of Cladonia, Citraria, Evernia, Parmelia are used as fodder. Usnic acid obtained from the Usnea and Cladonia species is used as an antibiotic against Gram-positive bacteria. Peltigera canina, the dog lichen is used as medicine for hydrophobia in ancient days.
Lobaria pulmonaria, lungwort are used for the diseases of lungs respiratory diseases and T. Parmelia is useful against epilepsy. Usnea species are good against urinary diseases.
Symbiosis in lichens "Lichens are fungi that have discovered agriculture" — Trevor Goward  A lichen is a composite organism that emerges from algae or cyanobacteria living among the filaments hyphae of the fungi in a mutually beneficial symbiotic relationship. The fungi benefit from the carbohydrates produced by the algae or cyanobacteria via photosynthesis.
The algae or cyanobacteria benefit by being protected from the environment by the filaments of the fungi, which also gather moisture and nutrients from the environment, and usually provide an anchor to it. Although some photosynthetic partners in a lichen can survive outside the lichen, the lichen symbiotic association extends the ecological range of both partners, whereby most descriptions of lichen associations describe them as symbiotic.
However, while symbiotic, the relationship is probably not mutualisticsince the algae give up a disproportionate amount of their sugars see below. Both partners gain water and mineral nutrients mainly from the atmosphere, through rain and dust. The fungal partner protects the alga by retaining water, serving as a larger capture area for mineral nutrients and, in some cases, provides minerals obtained from the substrate.
If a cyanobacterium is present, as a primary partner or another symbiont in addition to a green alga as in certain tripartite lichens, they can fix atmospheric nitrogencomplementing the activities of the green alga. In three different lineages the fungal partner has independently lost the mitochondrial gene atp9, which has key functions in mitochondrial energy production. The loss makes the fungi completely dependent on their symbionts. Phycobionts algae produce sugar alcohols ribitolsorbitoland erythritolwhich are absorbed by the mycobiont fungus.
The absence of this third partner could explain the difficulties of growing lichen in the laboratory. The yeast cells are responsible for the formation of the characteristic cortex of the lichen thallus, and could also be important for its shape.
The body thallus of most lichens is different from those of either the fungus or alga growing separately.
When grown in the laboratory in the absence of its photobiont, a lichen fungus develops as a structureless, undifferentiated mass of fungal filaments hyphae. If combined with its photobiont under appropriate conditions, its characteristic form associated with the photobiont emerges, in the process called morphogenesis.
Quite naturally, these alternative forms were at first considered to be different species, until they were found growing in a conjoined manner.Fungi Symbiotic Relationship With Plants
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.
All orchids are infected with this type of mycorrhizal fungus.
Orchid mycorrhizae are functionally different than in the above two types because of the unique nutritional needs of orchid plants. In most plants, the seed contains a food supply that will feed the embryo, until germination occurs, at which time the plant becomes photosynthetic and can produce its own food.
However, orchid seeds are very minute and contain a very small food reserve for the embryo. This food supply is usually depleted by the time that the first few cell divisions of the embryo has occurred. During this critical period of time between the end of their stored food supply until they become photosynthetic if they are photosynthetic orchids, many are notthey are dependent upon the mycorrhizae for survival.
Most orchid seeds will not even germinate until the fungal symbiont penetrates seed coat of the seed. Because of the lack of food in the embryo of the orchid, the fungus not only supplies minerals, but also organic compounds to the orchid such as carbohydrates and possibly other metabolites such as vitamins. Thus, it is the orchid that is deriving the carbohydrate from the fungus rather than the other way around.
Unlike the other mycorrhizal fungi, these fungi digest organic materials, from the surrounding environment of the orchid, into glucose, ribose and other simple carbohydrate and these nutrients are translocated into the orchid to support their own growth. The relationships that orchid species have with the mycorrhizal fungi are variable and is dependent on their nutritional needs. Some orchids become photosynthetic when their leaves develop while others are achlorophyllous.
So those that are photosynthetic do not require the mycorrhizae at that time, but often still retains the fungal symbiont as a partner. However, the achlorophyllous species will require it even as adult plants.
Some relationship are unique and very interesting. Many orchids are epiphytes, that is they live on other plants rather than in soil, and achlorophyllous. In experiments with orchid epiphytes, it has been demonstrated that the mycorrhizal fungus on the orchid roots also acts as a parasite upon the plant which the orchid is growing. In this type of relationship, food is being transferred, by the fungus, from the tree, on which the orchid is growing, to the orchid.
This brings up another interesting point concerning orchid mycorrhizal fungi. The fungus involved is often known to be a serious pathogen to most plants, but for some reason seems to be a benefactor to the orchid.
Commercially, orchids are grown with an external source of organic carbon compounds and sometimes vitamins.
However, this does not work with all orchid species. Ericaceous Mycorrhizae The mycorrhiza formed in this group is between fungi in the Ascomycota, and more rarely in the Deuteromycota, and species in the families Epacridaceae, Ericaceae and Pyrolaceae. Three subcategories are recognized, arbutoid, ericoid and monotropoid. We will briefly cover the latter two groups.
Ericoid Mycorrhizae This group is probably the most important, with respect, to its potential applications. Ericoid mycorrhizae have evolved in association with plants that are continually stressed by factors within the soil. The soil is typically extremely acid, low in available minerals because mineralization is inhibited.
Plants with ericoid mycorrhizae seem to have a high tolerance to these stresses and there is good reason to believe that this is related to the presence of the mycorrhizal fungus and that the survival of the host is dependent upon the fungus. Monotropoid Mycorrhizae One of the characteristics that we always attribute to plants is that they have chlorophyll and can produce their own food through the process of photosynthesis. However, this is not true of all plants.
The Monotropaceae and Pyrolaceae are two families of plants which are achlorophyllous. Thus, plants in these families are more dependent upon their mycorrhizal partners than plants which can carry out photosynthesis. The means by which food is obtained by these plants is similar to that of the epiphytic orchids described above.
However, morphologically, they are very different. The achlorophyllous host has mycorrhizae roots that appear to be formed by an ectomycorrhizal fungus, but the epidermal and outer cortical cells are penetrated by the fungus.
The fungus also forms an ectomycorrhizal relationship with a tree which is capable of photosynthesis. So, as in the case of the epiphytic orchids, the photosynthetic tree indirectly provides carbohydrates to these achlorophyllous plants, as well as to the fungus. Both hosts probably obtain their mineral requirements through the fungus. Lichens The most well known example of a symbiosis between fungi and plants is the lichen, if you will allow me to include algae as plants.
The concept of what constitutes a lichen has broaden significantly in the last 25 years to include some species of mushrooms, slime molds, and some members of the Zygomycota. However, we will discuss lichens in the traditional sense, as an association between a fungus and an alga that develops into a unique morphological form that is distinct from either partner.
The fungus component of the lichen is referred to as the mycobiont and the alga is the phycobiont. Because the morphology of lichen species was so distinct, they were once thought to be genetically autonomous until the Swiss Botanist Simon Schwendener described their dual nature in Prior to that time, because of the morphology of many of the "leafy" species of lichens, they were considered to be related to bryophytes, i.
Although, lichens are now known to be composite organisms, they are still named for the fungus part of the association since that is the prominent part of the lichen thallus.
Symbiosis: Mycorrhizae and Lichens
A thallus is an old botanical term used to describe "plants" that do not have leaves, stems and roots, and its origin goes back to a time when only two kingdoms were recognized in classifying organisms, i. Prior toorganisms such as algae, bacteria and fungi, were included in the plant kingdom. InWhitaker, proposed a five kingdom system which we still presently use.
Although, this term is now dated, it is still used to describe the "bodies" algae, fungi and of course lichens. The only group of organisms that are still considered to be plants, in which we still use the term thallus, to refer to the plant body, are the bryophytes.
Although the lichen thallus is composed of an algal and fungal component, lichens are not studied in mycology or phycology that part of botany that studies algae. Instead, they are studied in their own discipline, lichenology. There are relatively few lichen researchers. Of these most are taxonomist. As a result, there are still some basic questions concerning this symbiosis that are unanswered or at least up for debate. One of the most basic questions, that has been asked since the discovery of the lichen symbiosis, concerns whether lichens represent a true mutualistic symbiosis or nothing more than a variation of a host-parasite relationship.
There is evidence supporting both sides. That it represented a mutualistic symbiosis, in which the alga was believed to contribute the food supply through photosynthesis, and the fungus protected the alga from dessication, harmful solar radiation and provided the alga with water and inorganic nutrients, was postulated by Beatrix Potter, the writer and illustrator of Peter Rabbit, soon after Schwendener had determined the true nature of the lichen thallus.
In order to understand both sides of the issue, lets look at the morphology and anatomy of lichens. The Lichen Thallus In the traditional sense of lichens, their thallus can be artificially divided into four forms: Foliose Lichens Lichen thallus which is generally "leaf-like", in appearance and attached to the substrate at various points by root-like structures called rhizines.
Two examples of this thallus type is Pseudocyphellaria anthraspsis and Hypogymnia imshaugii. Because of their loose attachment, they can easily be removed. These are the lichens which can generally be mistaken for bryophytes, specifically liverworts. It is possible, or even probable, that herbaria still contain lichens that have been mistakenly identified as liverworts.
If we look at these a foliose lichen in longitudinal section, from top to bottom, we would be able to distinguished the following layers: Often composed of tightly interwoven mycelium, which gives it a cellular appearance.
This cellular appearance is referred to as pseudoparenchymatous. Composed of interwoven hyphae with the host algal cells. This is the ideal location for the algal cells. Beneath the upper cortex so that it receives the optimal amount of solar radiation, for photosynthesis, but not direct solar radiation which would be harmful. Composed of loosely interwoven mycelium. Layer is entirely fungal. Usually same composition as the upper cortex and attached to the substrate by root-like structures called rhizines.
The rhizines are entirely fungal, in origin, and serve to anchor it to the substrate. Thus, the foliose lichens also have what is referred to as a dorsiventral thallus, i. Crustose Lichens Lichen thallus which is very thin and flattened against the substrate.