Symbiosis: Mycorrhizae and Lichens
The interaction that can occur between two different types of species comes in different The term mycorrhiza comes from the Greek and means “fungus root”. Other products of the fungal metabolism are an effective protection against pests. Lichens: symbiotic organisms composed of fungi and algae. External Links · Donate. Colorful Lichens on stone 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 fungus provides its Lichens also make about known "secondary products". It is thought that these. Symbiosis is the ecological interaction between two organisms that live together. In a mycorrhizal association, the fungal mycelia use their extensive network of plant supplies the products of photosynthesis to fuel the metabolism of the fungus. This cross-section of a lichen thallus shows the (a) upper cortex of fungal.
Mycorrhizal Fungi and Plant Roots: A Symbiotic Relationship
Every cell in every plant and animal, many protists, and all fungi contains organelles known as mitochondria. Commonly described as the power sources of the cell, they build the molecule ATP adenosine triphosphatewhose complex bonds, when broken, release the energy needed to drive other cellular functions.
These organelles also reproduce on their own by splitting, just as bacteria do. It probably began with the bigger cell engulfing a bacterium to eat it. That combination became the primordial line that ultimately led to the larger life forms we know today. Plants have an additional type of organelle in their cells: That in turn fuels the construction of sugars from ordinary carbon dioxide and water, with oxygen given off as a byproduct.
Like mitochondria, chloroplasts have their own DNA and reproduce independently. As far as scientists can tell, the chloroplasts are almost certainly a strain of cyanobacteria. Widespread in early seas, those microbes were among the first — and maybe the very first — organisms to develop photosynthesis. At some point, like the ancestors of mitochondria, ancient cyanobacteria merged with larger, single-celled organisms.
Once again, it may have started when a bigger cell engulfed a smaller one, in this case a cyanobacterium that survived to carry on its sunlight-driven routines. The sugars it contributed led to a better-than-average survival rate for subsequent generations of both species as they reproduced. Their descendants developed into unicellular algae, then multicellular algae, and then — with the help of symbiotic fungi — land plants. You, I, the rest of humanity, and just about every visible creature we relate to as wildlife, pets, livestock, crops, ornamental plants, and so on, are symbionts, joint ventures in the business of existence, partnered-up from head to toe or root with invisible life forms.
To me this means that whether you are lost in the wild, mowing a suburban lawn or sitting on the top floor of a skyscraper in an empty, sanitized room, you are never really alone and never truly separate from nature, no matter what you feel or prefer to believe. Wildlife biologist, author, and longtime contributor to National Geographic, Douglas H.
Chadwick has spent much of his career among wild animals — very big wild animals. Yet ever since receiving his first microscope as a child, he has been equally fascinated by miniscule life-forms.
It kept me focused and intrigued all at the same time. I'm not entirely sure how researching apple trees to grow in my zone lead me down this path but I feel more knowledgeable, enlightened and soo very curious by doing so. I'm gonna be up all night reading up on mycorrhiza and its benefits, seriously exciting stuff! 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.
Sectional views, illustrating how the three thallus types of lichens differ. The entire lower surface is attached to the substrate. These lichens are so thin that they often appear to be part of the substrate on which they are growing. The following link shows an image of several lichen thalli. Crustose species that are brightly colored often give the substrate a "spray-painted" appearance.
The thallus has the upper cortex, algal and medullary layers in common with the foliose lichens, but does not have a lower cortex. The medullary layer attached directly to the substrate and the margins are attached by the upper cortex. This type of lichen is tightly flattened to its substrate and the entire lower surface medulla is attached, making it impossible to remove the thallus from its substrate.
Fruticose Lichens The thallus is often composed of pendulous "hair-like or less commonly upright branches finger-like. The thallus is attached at a single point by a holdfast. In cross section, the thallus can usually be seen to be radially symmetrical, i. The layers that can be recognized are the cortex, algal layer, medullary layer, and in some species the center has a "cord" which is composed of tightly interwoven mycelium.
Other species have a hollow center that lack this central cord. Fructicose lichen thallus is attached to its substrate at a single point, but finding that point is not that easy!
Biology of Lichens In looking at the anatomy of the lichen, it is obvious that there is interaction between the phycobiont and mycobiont, but what kind of interaction is occurring. One school of thou0ght is that the alga produces the food material and that the fungus protects alga from desiccation, high light intensities, mechanical injuries and provides it with water and minerals.
This is the reasoning that many introductory text books have adopted and they define a lichen as a mutualistic symbiosis. However, in studies that have been done that examines the alga-fungus interface, it can be clearly seen that haustoria, specialized feeding structures present in parasitic fungi, penetrate the alga cells.
Thus, many lichenologist have defined this relationship as a controlled form of parasitism. There is more evidence and I would like to go over some of these. Illustration of haustoria penetrating algal cells give evidence that the lichen symbiosis is really a controlled form of parasitism. Conditions outside these parameters will usually be fatal for most species of fungi and algae. However, lichens occur all over the world. They even occur in arctic and hot, dry desert areas where few organisms can live or even survive.
Thus, the lichen is able to exploit habitats that few other organisms are able to utilize that seem likely to be the result of their mutualistic, symbiotic relationship. Another experiment that demonstrates that lichens represent a mutualistic symbiotic relationship was carried out in the laboratory by Vernon Ahmadjian.
Although, it is not difficult to separate the myco- and phycobiont components of the lichen, and grow them separately in the laboratory, putting the component back together is another story. For many years it was not possible to put the two together to reform the lichen thallus. The reason for this was the method that was used in attempting to reform the lichen thallus.PGC Lectures :Mycorrhiza
These types of media did not work. Ahmadjian reasoned that if the lichen represents a symbiosis, the reason that the relationship formed was because, in nature, neither one could obtain all the nutrients necessary for survival and that only after the two organisms interacted was it possible. Thus, Ahmadjian created a minimal medium, which would not support the growth of either the myco- or phycobiont, and inoculated them into that medium.
This method successfully reformed the lichen thallus, in the laboratory, for the first time. Although, it would appear that there is a great deal more evidence supporting the lichen thallus as a product of mutualistic symbiosis, there are still many who believe that the relationship is that of a balance parasitism that favors the mycobiont.
A Few Words on The Lichen Component Although there are approximately 13, species of lichens recognized, the number of taxonomic groups of fungi and algae that produce the lichen thallus are few. Mycobionts In the traditional sense of lichens, which is how we are defining lichens, the fungal components are always in the Ascomycota, specifically in those groups that form their asci and ascospores in fruiting bodies.
The fungi involved in the lichen symbiosis are never found to be free-living in nature.
Phycobiont Regardless of whether we are using the traditional or expanded definition of lichens, the algae involved in the association are the same. Of all the different species of algae that are known, only the divisions Chlorophyta "green" algae and Cyanophyta "blue-green" algae or Cyanobacteria are involved in lichen formation.
The latter are actually bacteria rather than algae although they were classified as such once upon a time. Furthermore, within these divisions, only a few genera are involved in the lichen symbiosis. Some genera, such as Trebouxia, are known to only occur in lichens and are not free-living, but there are also examples that are free-living.
Economic Relevance Economically, lichens have little significance. Perhaps this is why there is so little interest in this group of organisms.
One way that they have been utilized is in the extraction of blue, red, brown or yellow dyes in the garment industry. Also, the indicator pigments used in litmus paper was also derived from lichens.
Previously, we briefly mentioned lichens as a source of pharmaceutical compounds. You can include some "folk" remedies in this category as well. They are also used in the cosmetic industry, in the making of perfumes and essential.
Finally, some species have been used as food. One species, Lecanora esculenta, is a species that grows in the mountains near Israel and are typically blown free from their substrate. Desert tribes grind up the lichen, dry it and mix it with dry meal to form a flour.
It is postulated that this is the species lichen that is referred to as "Manna from Heaven" when Moses led the Hebrews across the desert during biblical time. One species, Cladonia rangiferina reindeer mossis fed upon by reindeers and cattle. This has led to the discovery that lichens readily absorb radioactive elements. After open-air, atomic testing, both Alaskan Eskimos and Scandinavian Laplanders were found to have high levels of radioactive contamination, which they had absorbed from eating reindeer, which in turn ate lichens.
Other Significant Uses for Lichens Lichens are conspicuously absent in and surrounding cities because many species are sensitive to pollution, especially to sulfur dioxide and flourine, which are common pollutants.
For this reason, they have been commonly used as indicators of pollutants. In urban areas, where lichen surveys have been carried out, the absence of certain indicator species is used as early warnings of decrease in air quality.
Lichens also play a very significant role in nature. They are the pioneers in rocky substrates, where there is no soil. Lichens break down the rocky substrate into soil and their decomposing thallus fertilize the newly produced soil, making it possible for the plant habitation. Reproduction Reproduction of the lichen is entirely asexual. It may occur by soredia sing.: This is best seen in a sectioned lichen. The other means of asexual reproduction is by isidia sing.: Ascospores and conidia also form, but these will only reproduce the fungus.
It is assumed that these structures will come in contact with a suitable algal host and resynthesis the lichen thallus. However, the latter are not thought to be significant in lichen reproduction. From left to right: Clusters of soralia, two soredia, as seen through the microscope, isidia and section through soredium.
The part of the lichen that is composed of interwoven hyphae with the host algal cells. A category of Endomycorrhizae characterized by the production of globose structures, called vesicles, and branched, tree-like structures called arbuscules, in the cortex of the root cells.
The root cells lyse these structures and receive the minerals from the fungus, in this matter. Such relationships are usually not obligate, and neither species will be adversely affected if the relationship does not occur.
Lichen that is very thin and flattened against the substrate. This type of lichen lacks a lower cortex and is attached to its substrate by the medullary layer. Thus, these lichens are very thin and often appear to be part of the substrate on which they are growing.
Lichens that have a leafy appearance and are attached to their substrate by structures called rhizines. Lichens that are often composed of pendulous "hair-like or less commonly upright branches finger-like and attached at a single point.
In cross section, the thallus can usually be seen to be rounded, i. Thus, there is a single cortex layer. Asexual reproductive structures found on lichens that are upright, cylindrical to swollen in appearance. Structures break off and can form another lichen. The symbiotic relationship between a fungus and an alga that develops into a unique morphological form that is distinct from either partner. The fungal component of the lichen.
In the traditional sense, the fungus is a member of the Ascomycota. The symbiotic relationship between the roots of plants and fungi. The term mycorrhiza literally means root fungus, but in the broad sense of the term, the interaction does not always occur only with the roots of plants, a mycorrhizal relationship also includes plants that do not have roots, such as and bryophytes mosses and liverworts.
The algal component of the lichen. The alga is usually a member of the Chlorophyta or Cyanobacteria. Structures found on the lower cortex of foliose lichens and functions in anchoring the lichen to the substrate.
Asexual reproductive structures found on lichens that form as a result of the rupture of the cortex, exposing the algal layer, which break into spore-like structures composed of a few algal cells and hyphae that are dispersed by wind. They also dry out slowly, making it possible for the photosynthesizing partner s to make food for as long as possible.
This ability to quickly absorb and retain water from many sources makes it possible for lichens to live in harsh environments like deserts and polar regions, and on exposed surfaces like bare rocks, roofs and tree branches. The thallus, or lichen body, comes in four shapes: Most lichens grow slowly, probably because they live in environments where water is available for only short periods.
They tend to live for many years, and lichens hundred of years old can be used to date the rock surfaces on which they grow. Lichens spread mostly by small pieces of their body being blown around.
Mycorrhizal Fungi and Plant Roots | MOTHER EARTH NEWS
All the partners in the original lichen body are present in the fragment, so growth can begin immediately. Some lichens create soredia, balls of tissue made just for dispersal. Although the fungus is the major partner, dispersal by spores is rare. Uses for Lichens Lichens have many uses.
They differ in their sensitivity to air pollution, and the presence or absence of different lichens in an area has been used to map concentrations of pollutants.
Foliose lichens are used to represent trees in model train layouts. Lichens also make about known "secondary products".
It is thought that these chemicals are produced by lichens as defenses against disease and parasites, and, in some cases, to make the lichen taste unpleasant to animals. Some of these compounds are now used as anti-viral and anti-bacterial medications.
Other secondary products are used to make everyday life more colorful and pleasant.