BIO Powerpoint
LICHEN
Lichen
Lichen
Lichen do not have a common lineage because they are because of a combination of several species from different kingdoms such as Kingdom Monera, Protista, among others. These organisms are not grouped based on the species of the cyanobacteria or algae in them hence they have an identical binomial name as the thallus present in them (Carlile, Watkinson, & Gooday, 2005). Although these organisms typically reproduce sexually and asexually, the sexual reproduction of these organisms is no longer active and this means they mostly reproduce asexually by vegetative. Taxonomists have been able to identify about 20,000 species of lichen across the world; these are the species that are known so far. Most lichen have thallus that is different from that of alga or fungus; they develop into undifferentiated fungal filaments known as hyphae or as structure less when they are grown in the laboratory with its photobiont absent. In strange situations, one lichen fungus can grow into many lichen forms when it grows with either cyanobacterial or green algal symbiont. Under suitable conditions, lichen can combine with its photobiont, its features linked to the photobiont appears a process known as morphogenesis as well as symbiotic relationships, reproduction habits and growth rates.
The lichen symbiotic associations can either be parasitic, mutualistic or even commensalism (Grant & Long, 1981). The organisms can occur in other organisms as parasites obtaining food and shelter in the organisms. This type of symbiosis does not benefit the host but benefit the parasite itself, at the end of the day, the host organism will be affected negatively. The photobiont cells are in most cases obliterated. The association does not come to an end because the rate at which the destruction of cells is destroyed equals to the rate at which they are reproduced. Lichen symbiosis is more of a commensalism or parasitic other than mutualistic. Green Algal (Chlorophyta), which is a photobiont partner in lichen, originates from simple eukaryotic or prokaryotic organisms, the partner could exist independently unlike the fungal partner which cannot independently exist in alone. Cyanobacteria or Algae synthesize their own food a process known as photosynthesis reducing carbon(iv)oxide in the atmosphere into sugars (organic carbon) to feed the symbionts. This enables the fungus to obtain food, in return cyanobacteria or algae obtain shelter from the filaments of the fungus, and the filaments also collect nutrients and moistures from the environment, hence acting as a point of attachment to it. Lichen are one of the successful symbioses since they can inhabit a wide range of geographical locations.
Unlike of the organisms which have a faster growth rate (Sumbali & Mehrotra, 2009), lichen have a slow growing rate amounting to less than a millimeter annually. The rate of growth among the different species of lichen also differs with growth rate as slowly as about 0.5mm and others as fast as 0.5 m annually (Sumbali & Mehrotra, 2009). The four forms of lichen, fruticose, foliose, squamous and crustose have different growth rate with most of crustose, crust like which grows tightly on the surface of the substrate growing 1-2mm in diameter after every twelve months. The anatomy of lichen is similar despite the difference in the growth forms. Foliose, a leaf-like having flat layers of tissues that are unbound tightly while fruticose is freely standing with branches. On its outer surface in contact with the external environment are the filaments which are tightly packed to forming the cortex. This is a dense layer protecting it from penetration by other harmful organisms; the cortex also serves to reduce the damage of alga cells by the light of high intensity. The same way photosynthetic cells in a leaf are arranged loosely to allow free circulation of air, algal cells are also distributed immediately below the cortex where the density of fungal filaments is low. Medulla is the next layer after the algal layer, it is comprised of loosely packed fungal filaments, for example in the foliose lichen, there exist the second cortex layer beneath the medulla, this is a diagnostic feature for foliose lichen.
The relationship of how the lichen is formed, which is fungus and algae, was first discovered in the year 1867 by a Swiss Botanist Simon Schwenderner, since then several scientists have understood the most important partnership that leads to the production of lichen. Through his observation, he discovered that most organisms if not all are because of combinations of species that are of different origin. In his observation, he concluded that lichen arise due to collaboration between a photosynthetic partner algal or cyanobacterium and a single fungus. The algal synthesizes food using solar energy and the carbon (IV) oxides to give rise to sugars. In return, the fungi form a structure that protects its photosynthetic partner against any interference from the environment. Several studies have been carried out on how lichen are formed, one of the studies was conducted by the University of Montana under the supervision of mycologists M.Catherine Aime.
Some of the researchers in their research identified the mechanism that lichen used to repel away predators however, research also revealed that lichen have basidiomycete yeasts (Webster, J., & Weber, R. (2006) that produces chemicals that the lichen use to repel its predators. On the other side of things, there are several studies that are underway to determine what kingdoms that lichen can enter mutuality with, and not repel. So far, the only kingdoms that have a mutual relationship is Monera and Kingdom Protista. Researchers want to establish whether this type of relationship can occur between the lichen and organisms from other kingdoms as well. New studies are also being conducted on the relationship to determine more substance produced by the photobionts(algae) apart from erythritol, sorbitol, and ribitol (sugar alcohols). More and more botanists and taxonomists are becoming interested in the relationship and this means we will expect more and more discoveries on the same.
Conclusion
Lichen are as a result of a combination of different species which include Kingdom Monera, Protista, among others hence these group of organisms does not have a specific lineage. These organisms could reproduce both sexually and asexually by vegetative reproduction, the organisms have ceased from reproducing sexually. About 20,000 species of these organisms have been discovered. Given suitable conditions, these organisms can mingle its photobiont and as a result, photobiont features appear (morphogenesis). The growth rate of these organisms is a bit slower compared to other living organisms. Symbiotic relationship experience in the organism can either be mutualistic, commensalism or even parasitic. Scientists are still learning about the lichen, and their behavior has much to offer.
Reference
Carlile, M. J., Watkinson, S. C., & Gooday, G. W. (2005). Fungi.
Grant, W. D., & Long, P. E. (1981). Environmental Microbiology. Boston, MA: Springer US.
Sumbali, G., & Mehrotra, R. S. (2009). Principles of microbiology. New Delhi: Tata McGraw-Hill.
Webster, J., & Weber, R. (2006). Introduction to fungi. Cambridge: Cambridge University Press.
