Presentation on theme: "Lichens Lecturer: Asst. Prof. Dr. İsmail EKER. Lichen internal structure An association of a fungus and a photosynthetic symbiont resulting in a stable."— Presentation transcript:
Lichen internal structure An association of a fungus and a photosynthetic symbiont resulting in a stable vegetative body having a specific structure Chlorophyta or Cyanobacteria + Ascomycota or Basidiomycota or Deuteromycota
Symbiotic association Both partners gain water and mineral nutrients mainly from the atmosphere, through rain and dust. Benefits for fungus are clear, it receives –organic compounds as C and energy source from algae or receives N source from cyanobacteria –O 2 source Benefits for algae are less clear-cut –Fungus produces substances that absorb water which is provided to alga –Protects algal cells from mechanical injury, predation, and high light intensities –Association allows alga to achieve a wider distribution than if free-living and alga may use the fungus to anchor to a substrate –CO 2 source Extended periods of high moisture lead to the fungus killing the alga ↑ O 2, food ↓ ↑ CO 2, H 2 O CO 2, H 2 O ↓ alga fungus
Lichens are unique as a symbiotic relationship because they look and behave quite differently from their component organisms. Lichens are regarded as organisms in their own right and are given generic and species names. about 30,000 species of lichen worldwide, covering 8% of the land surface. Most are in the Ascomycota – ratio of lichenized to nonlichenized Ascomycota is 14,000 : 15,000 Ca. 23 genera of algae and 15 genera of cyanobacteria found in lichens, 90% of lichens contain Trebouxia, Nostoc or one other genus Green algae – Trebouxia sp. is a common genus, found in 75% of lichens in temperate zone. Trebouxia is not very successful as a free- living alga General characteristics of Lichens Cyanobacteria – Nostoc sp. is a common genus Classification–based on morphology of fungal symbiont: Ascolichens and Basidiolichens
Widely distributed – grow on soil, rocks, trees, marine or intertida – cold to hot, arid to moist May exist where other organisms can’t – surface of desert rocks, alpine, arctic, etc. When lichen thallus is wetted, absorbs water quickly by gelatinous matrix in the cortex. As thallus dries, growth process slows and stops Exhibit low growth rates – many grow at rates of 1-4 mm/yr, up to 9 cm/yr Light – variable – some prefer low light intensities, others high Lichens are many times the first organism to settle in an area with no soil
Thallus morphology The "body" of a lichen is termed the thallus, and its general shape is used to group lichens into four broad categories. branched, strap shaped or threadlike thallus, upright or hanging 1. Fructicose (shrubby)
Ascocarp of fungus Fungal hyphae Algal layer Soredia Fungal hyphae Algal cell Reproduction Sexual reproduction – characteristic of fungal symbiont. Thought that after ascospores germinate, they make contact with algal cells. Asexual reproduction – fragmentation (soredia - algal cells enveloped by hyphae)
Scanning electron micrograph (SEM) of a lichen. The round structures are the fruiting bodies (apothecia), which contain the reproductive spores of the fungi Apothecia
Air pollution Lichens can grow in extreme climate conditions (there are lichens that survive from -198 0 C to 50 0 C). Even though lichens are very resistant to natural environmental extremes – they are extremely sensitive to air pollution – particularly SO 2 Obtain nutrients from atmosphere, not soil Both species composition and numbers of thalli decline from edge to center of industrialized areas Some are useful as indicator species Ecological importance
as food for many arctic animals, such as reindeer. Cladonia rangiferina (Reindeer Lichen) is aeten by many arctic animals and sometimes by people. A desert lichen, Lecanora (Manna Lichen) is collected and eaten in Libya. dyeing yarns and as acid-base indicators such as litmus (Roccella tinctoria and Rocchella fuciforme (Litmus lichens)). Orcein, derived from a lichen, is used extensively in cytological preparations for staining chromosomes. Synthetic dyes have now replaced lichen dyes for commercial and laboratory use. Usnic acid derived from lichens (especially Usnea sp.) has antibiotic properties againist a number of fungi and bacteria, including human pathogens. Some lichens (Evernia prunastri (Oak lichen); Pseudoevernia furfuraceae (tree lichen)) are the sourch of an oily substance used in perfume industry. Economical importance A number of chemicals are only synthesized by the symbiosis – dyes, antibiotics, essential oils, litmus (over 600 different chemicals unique to lichens have been identified)
Mycorrhizae Lecturer: Asst. Prof. Dr. İsmail EKER
Mycorrhizzae Symbiosis Mycorrhiza (plural, -ae or –as) - Greek - “mycos (fungus)” + “rhiza (root)” Mycorrhizae is a symbiotic relationship with a plant’s roots and a fungus that is primarily Mutualistic (benefits both) but can be Pathogenic (causing harm to plant). Mycorrhizae is most useful in nutrient poor soil. Unlike normal roots, Mycorrhizae are thinner and are generally more wide-spread (up to 8m away!), which allows them to search for nutrients (P, Zn, Cu in particular) and water more effectively. While Mycorrhizae has a far more effective method of gathering nutrients and water for the plant, the fungi also has access to the Glucose and Sucrose provided by the plant. Some mycorrhizae can protect roots from other fungi Common: 90% of plants do this! Few higher plants do not form mycorrhizal associations, 10-20% including some aquatic vascular plants and members of the Brassicaceae, Cyperaceae, and Juncaceae.
How Do Mycorrhizae Function? Fungal hyphae release enzymes (chitinase, peroxidase, cellulase, protease) which allows them to digest and penetrate substrates. Secretion of enzymes breaks down tough organic substrates that can then be absorbed and used by the fungus and/or host plant as energy and nutrient sources for growth and reproduction. Both members benefit from their interaction. Plants receive mineral nutrients and water; mycorrhizal fungi receive carbon and a place to live.
Plant on left grown without mycorrhizal fungi Benefits to Plants Hyphae increase surface area of roots for increased absorption of soil nutrients. Increase water uptake and aid drought resistance to plants Resistance to some root pathogens due to thick hyphal mantle Increase plant tolerance to soil temperature extremes, pH extremes, toxic heavy metals, and transplant shock Aid in plant establishment on nutrient poor soils (mining reclamation and revegetation projects) Increase plant size in short time period (forestry) Reduce fertilizer requirements Cut down production costs Benefits to World Agriculture
Types of mycorrhizae Glomeromycetes form symbiotic endomycorrhizae with plant roots: supplying minerals to the roots and obtaining carbohydrates in return. Specialized hyphae (arbuscules) perform this exchange by pushing in the plasma membrane. Endomycorrhizae (Vesicular arbuscular mycorrhiza) – hyphae penetrate cells of plant Ectomycorrhizae (ectotrophic, sheathing) – hyphae of fungus do not penetrate cells of plant root
1. Endomycorrhizae: Vesicular arbuscular mycorrhiza (AM) (Arbuscular mycorrhizal fungi) All are in the Zygomycota in the Glomales – or newly proposed phylum Glomeromycota Include ca 130 species in 6 genera – infects 300.000 plant species Found in species in all divisions of terrestrial plants – widely distributed in annuals, perennials, temperate and tropical trees, crop and wild plants All are obligate biotrophs Form extensive network of hyphae even connecting different plants Appear to be the most common type of mycorrhizal association with respect to the number of plant species that form them Typically disintegrate after ca 2 weeks in plant cell and release nutrients
2. Ectomycorrhizae (EM) 2000 plant species – primarily temperate trees and eucalyptus Over 5000 species of fungi have been shown to form ectomycorrhizae. Basidiomycota – Agaricales (many mushroom species) and Ascomycota – Pezizales – cup fungi and truffles Major species of coniferous and deciduous trees Rare to find uninfected trees In some trees, the association is obligate, in others facultative Mycorrhizal association important in forestry Plant roots are enclosed by a sheath of fungal hyphae – fungal mycelium penetrates between cells in cortex of the root Fungal tissue may account for up to 40% mass of root Hyphae also extend out into the soil – extramatrical hyphae. Forms extensive network of hyphae even connecting different plants
Ectomycorrhizal root: contains a fungal sheath Parenchyma of root cortex is surrounded by hyphae
Why mycorrhiza? Roots and root hairs cannot enter the smallest pores
Why mycorrhiza? Root hair Smallest hyphae Roots and root hairs cannot enter the smallest pores Hyphae is 1/10 th diameter of root hair Increased surface area Surface area/volume of a cylinder: SA/vol ≈ 2/radius
Inoculated with mycorrhizae Not inoculated with mycorrhizae Why mycorrhiza? Roots and root hairs cannot enter the smallest pores Hyphae is 1/10 th of root hair Increased surface area Extension beyond depletion zone
Why mycorrhiza? Roots and root hairs cannot enter the smallest pores Hyphae is 1/10 th of root hair Increased surface area Extension beyond depletion zone Breakdown of organic matter C – C – NH 2 --> C – C + NH 3
Benefits of Mycorrhizae Tolerant of harsh conditions –fungi are more tolerant of acidity, elemental toxicity and high soil temperatures than are higher plants and able to, in some cases (ectomycorrhizae), shield the root from these condition. –Lower levels of heavy metals generally found in mycorrhizal plants than nonmycorrhizal plants. Increased seedling survival –Mycorrhiza promotes plant survival, whether new seedlings or out- planted container stock. –Survival of inoculated plants can be up to five times the survival of uninoculated plants. –Improved survival is no doubt due to a combination of mycorrhizal benefits, including faster growth to help overtop weeds, protection from pathogens, and improved drought tolerance.
Mycorrhizal vs non-mycorrhizal plantMycorrhizal and non-mycorrhizal plant
Mycorrhizae and Plant diversity Biodiversity of belowground fungal symbionts increases biodiversity of above ground plants Increased access to nutrients becomes restricted under competitive conditions Differences in functional capacity of a specific fungus-plant combination appear to explain the effect In ecosystems, increased functional capacity allows one plant species to perform better than others Restored plant communities have been found to be more diverse when mycorrhizal fungi are present when both inoculated and uninoculated areas receive the same seed mix.
Mycorrhizae and Plant diversity Basis for fungal species richness on plant biodiversity and production No symbiontsOne symbiont Increasing diversity
Mycorrhizae and Plant diversity Basis for fungal species richness on plant biodiversity and production No symbionts One symbiont Two symbionts Increasing diversity Increasing productivity
Basis for fungal species richness on plant biodiversity and production No symbiontsOne symbiontTwo symbiontsFour symbionts Increasing diversity Increasing productivity Mycorrhizae and Plant diversity
The aquatic fern Azolla sp. is the only fern that can fix nitrogen. It does so by virtue of a symbiotic association with a cyanobacterium (Anabaena azollae). Nitrification cannot occur in the presence of oxygen, so nitrogen is fixed in specialized cells called heterocysts. These cells have an especially thickened wall that contains an anaerobic environment. This has been used to great advantage in the cultivation of rice, where the floating fern Azolla is actively distributed among the rice paddies. The fern houses colonies of the Anabaena in its leaves, where it fixes nitrogen. The ferns then provide an inexpensive natural fertilizer and nitrogen source for the rice plants when they die at the end of the season. Nitrogen: lots in atmosphere (79% N 2 ), but plants can’t use that Nitrogen fixation: Cyanobacteria and the other nitrification bacteria use N 2 to form NH 3 (ammonia) or NO 3 - (nitrate) About 90% of nitrogen fixation is done by bacteria Nitrogen fixation
Another cyanobacterium on the palm (Welfia regia) in an epiphyllic relationship It is believed that these bacteria transfer some % of fixed N to the plants through the leaf surfaces