Mutualisms between fungi and algae
One point of agreement is that the relationship allows lichens to colonize Remember, algae are green plants, primitive relatives of grass. Lichens are a mutualism formed between fungi and various groups of algae. also upright structures called podetia that eventually support apothecia (see below for green algae, the photobiont, and will be seen to be green if cut lengthwise. Hello, In lichens (blue-green algae) the algae benefit their fungal partner by .. this relationship between algae and fungi is known as symbiotic relationship in which both are mutually benefited. How do algae and fungi help each other?.
Other lichen fungi occur in only five orders in which all members are engaged in this habit Orders GraphidalesGyalectalesPeltigeralesPertusarialesand Teloschistales. 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. Fungi are incapable of photosynthesis because they lack the green pigment chlorophyll.
What Are Lichens?
That is to say, fungi cannot harvest light energy from the sun and generate their own nourishment in the form of carbohydrates. Instead, they need to seek out outside sources of food. They absorb nutrition from organic substances, that is, carbon containing compounds such as carbohydrates, fats, or proteins. On the other hand, algae and cyanobacteria can conduct photosynthesis, similar to plants.
In fact, chloroplasts, which are the site of photosynthesis in land plants, are adapted forms of cyanobacteria.
These early cyanobacteria were engulfed by primitive plants cells sometime in the late Proterozoic, or in the early Cambrian periodaccording to the University of California Museum of Paleontology. So when a fungus, which is the dominant partner in this relationship, associates with an alga usually from the green algae or cyanobacterium to form a lichen, it is providing itself with constant access to a source of nourishment.
He described it as the controlled growth of a carbon-providing organism, just like we grow wheat, rice or potatoes. He added that cyanobacteria also provide fungi with the additional benefit of nitrogen fixation. This is the biochemical reaction wherein atmospheric nitrogen is converted to ammonia, a more usable form of the element.
In return, algae and cyanobacteria secure a protected environment, especially from damaging ultraviolet rays. Finally, as lichens, fungi, algae and cyanobacteria are able to live in environments that they could not live in otherwise.
Fungi Symbiosis ( Read ) | Biology | CK Foundation
Weird World of Lichen: On his website dedicated to lichen, Alan Silverside, now retired from the University of the West of Scotland, gives the example of the fungus Sticta canariensis. This fungus is capable of forming two different lichen associations with an alga and cyanobacterium, yet both lichens are referred to as Sticta canariensis. This is how early lichens might have looked like million years ago.
It is the thallus that gives lichens their characteristic outer appearance. Lichen thalli come in many different forms.
Examples on Silverside's pages include foliose lichen, which look flat and leafy; fruticose lichen, which have a wiry, tufted appearance; squamulose lichen, which have flat, overlapping scales; and crustose lichen, which as the name suggests, form a tightly attached crust over the surface it inhabits. In general, the inside of the lichen thallus appears stratified, with the mycobiont and photobiont cells arranged in layers.
MUTUALISMS BETWEEN FUNGI AND ALGAE
According to the U. Forest Servicethe outer layer or cortex is made up of thick, tightly packed fungal cells. This is followed by a segment with the photobiont either green algae or cyanobacteria.
If a lichen has both an algal and a cyanobacterial partner, the cyanobacteria can be seen within little compartments above the upper cortex. The final layer is the medulla, with loosely arranged fungal cells that look like filaments.
Symbiosis in lichens
Extensions below the medulla, which are called basal attachments, enable lichens to adhere to various surfaces. Typical basal attachments include rhizines, which are fungal filaments extending from the medulla, and a single, central structure called the holdfast, which latches onto rocks. The Forest Service gives the example of a foliose lichen called the umbilicate lichen, where the holdfast resembles an umbilical cord.
As an exception to the general thallus structure, jelly lichens do not have a layered or stratified thallus. The mycobiont and photobiont components sit together in a single layer.