Lichen protein affinity towards walls of cultured and freshly isolated phycobionts and its relationship to cell wall cytochemistry

Abstract The binding capacity of protein fractions ( M _r > 8000) from five lichens, Hypocenomyce scalaris, Hypogymnia physodes, Ramalina fastigiata, Umbilicaria pustulata and Xanthoria parietina was tested towards their freshly isolated phycobionts and towards ten cultures of phycobionts, five of which were from the above-mentioned lichens. The protein fractions from H. scalaris, R. fastigiata, U. pustulata and X. parietina bind intensely to a cultured Pseudotrebouxia from H. physodes and a cultured Trebouxia from X. parietina , but not to the other cultured algae, and not to the freshly isolated algae. A protein fraction between M _r 3500 and 8000 from H. physodes shows a faint binding to its own cultured algae. The nature of the binding and its relevance in connection with the mutual recognition of alga and fungus are briefly discussed.     

Water Status of Green and Blue-green Phycobionts in Lichen Thalli after Hydration by Water Vapor Uptake: Do They Become Turgid?

It is known from previous investigations that dry lichens with green algae are able to recover net photosynthesis through rehydration with water vapor, whereas all blue-green lichens tested so far lack this ability. The REM micrographs of the present study show that the green phycobionts (Trebouxia spec.) of Ramalina maciformis become turgid only after water vapor uptake. In contrast, the blue-green phycobionts (Nostoc spec.) of Peltigera rufescens do not differ in appearance from the dry state, even when the thallus has reached equilibrium with the water vapor-saturated air; they require liquid water for turgidity. It is hypothesized that, after humidity hydration, water content is not sufficient for reestablishment of a functioning osmotic cell system in the blue-green phycobiont.     

三种荒漠地衣共生菌藻的耐热性研究

作为沙漠生物地毯工程研究的组成部分,对荒漠地衣石果衣Endocarpon pusillum、节瘤微孢衣Acarospora nodulosa以及荒漠微孢衣A. schleicheri的共生菌藻进行了耐热性研究。结果表明,3种荒漠地衣的共生菌藻在湿润条件下对温度的最大忍受力仅为50℃,而在干燥条件下石果衣的共生菌藻的最大忍受力均为75℃,而其他两种地衣共生菌藻的最大忍受力均为80℃。3种荒漠地衣共生菌、藻分别对高温胁迫的耐受力,在干燥状态下均比在湿润状态下明显增高。     

Cytochemical location of urease in the cell wall of two different lichen phycobionts

The enzyme urease has been located in the cell wall of recently isolated phycobionts from Evernia prunastri and Xanthoria parietina lichens. Cytochemical detection is achieved by producing a black, electron-dense precipitate of cobalt sulfide proceeding from CO(2) evolved from urea in the presence of cobalt chloride. Cellular fractionation reveals that about 80% of total urease activity was associated to the cell wall on both phycobionts whereas only 20% was recovered as soluble protein.     

Detection of polysaccharides and ultrastructural modification of the photobiont cell wall produced by two arginase isolectins fromXanthoria parietina

Morphological and structural studies carried out inXanthoria parietina reveal some fungal mechanisms to regulate both growth and development of the phycobiont as well as the number of photobiont cells present in the holobiont. This regulation is performed by phenolic acids and glycosyl-enzymes. An ultrastructural analysis using the polysaccharide detection technique PATAg shows that plasmolysis of cells occur when freshly isolated phycobionts are incubated with two arginase lectins (ABP, algal binding protein and SA, secreted arginase), with development of large cytoplasmic vesicles filled with amorphous polysaccharides that are exocyted to the periplasmic space. Finally, membranes of organelles and plasma membrane are altered and the cell wall is broken. The results presented here provide evidence of a possible fungus-to-algal action as deduced from the hemiparasitic symbiosis theory.     

Water vapor uptake and photosynthesis of lichens: performance differences in species with green and blue-green algae as phycobionts

Summary Dry lichen thalli were enclosed in gas exchange chambers and treated with an air stream of high relative humidity (96.5 to near 100%) until water potential equilibrium was reached with the surrounding air (i.e., no further increase of weight through water vapor uptake). They were then sprayed with liquid water. The treatment took place in the dark and was interrupted by short periods of light. CO₂ exchange during light and dark respiration was monitored continuously. With no exception water uptake in all of the lichen species with green algae as phycobionts lead to reactivation of the photosynthetic metabolism. Further-more, high rates of CO₂ assimilation were attained without the application of liquid water. To date 73 species with different types of Chlorophyceae phycobionts have been tested in this and other studies. In contrast, hydration through high air humidity alone failed to stimulate positive net photosynthesis in any of the lichens with blue-green algae (Cyanobacteria). These required liquid water for CO₂ assimilation. So far 33 species have been investigated, and all have behaved similarly. These have included gelatinous as well as heteromerous species, most with Nostoc phycobionts but in addition some with three other Cyanophyceae phycobionts. The same phycobiont performance differences existed even within the same genus (e.g. Lobaria, Peltigera) between species pairs containing green or blue-green phycobionts respectively. Free living algae also seem to behave in a similar manner. Carbon isotope ratios of the lichen thalli suggest that a definite ecological difference exists in water status-dependent photosynthesis of species with green and blue-green phycobionts. The underlying biochemical or biophysical mechanisms are not yet understood. Apparently, a fundamental difference in the structure of the two groups of algae is involved.     

Proteins from the liehenXanthoria parietina which bind to phycobiont cell walls Localization in the intact liehen and cultured mycobiont

Summary A protein fraction, previously isolated from the lichenXanthoria parietina and known to bind to the appropriate culturedTrebouxia phycobiont, was visualized in the intact lichen thallus and cultured mycobiont by an indirect immunoperoxidase assay. The protein was localized in both the upper and lower cortices of the lichen thallus; it was also present in the cell walls of the mycobiont culturedin vitro. The possible role of this protein in the recognition, or initial interaction, between separated lichen symbionts is discussed.     

Spectral Properties of the Green Alga Trebouxia,a Phycobiont of Cryptoendolithic Lichens in the Antarctic Dry Valley

An algologically pure culture of the green alga Trebouxia, a phycobiont of cryptoendolithic lichens, was isolated from sandstone samples collected in the high-altitude polar regions of Antarctica. The absorption and second-derivative absorption spectra of acetone extract of the Antarctic phycobiont cells were studied in comparison with those of a Trebouxia phycobiont isolated recently from a Parmeliaceae lichen in the Mid-European climatic zone. The cells of the Antarctic phycobiont were characterized by a lower content of chlorophyll a and a higher ratio of chlorophyll b and carotenoids to chlorophyll a as compared to the Mid-European phycobiont. Furthermore, the carotenoids of the Antarctic phycobiont were more diverse. The low-temperature fluorescence spectra of the Antarctic phycobiont were characterized by an increased intensity of the short-wavelength fluorescence peak of chlorophyll aand a diminished intensity of fluorescence in the long-wavelength spectral region.     

Die Ultrastruktur einiger Flechten nach langen Trockenzeiten

Zusammenfassung Rhizocarpon geographicum, Umbilicaria pustulata undRamalina maciformis wurden für elektronenmikroskopische Untersuchungen ihrer Phycobionten kurze Zeit nach dem Sammeln dieser Flechten und nach verschieden langen Trockenperioden bis zu 4 Jahren fixiert. Die beobachteten geringen Änderungen in den Phycobionten nach langer Trockenzeit bestätigen die große Trockenresistenz der Flechten. Eine erneute Befeuchtung der Flechten führt im allgemeinen zum Auftreten von Stärke in den Phycobionten Chromatophoren und zu einigen anderen Änderungen, die von der Temperatur und der Belichtung während der Befeuchtung abhängen.

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The ultra structure of some lichens after long dry periods

Summary The ultrastructure of the phycobionts fromRhizocarpon geographicum, Umbilicaria pustulata andRamalina maciformis is described from thalli which were fixed short time after collecting them and after different periods of dryness up to four years. By demonstrating only little changes in the phycobiont ultrastructure of dry thalli their well known resistance to dryness could be confirmed. Rewetting the lichens induced the appearence of starch and some other alterations in the phycobiont ultrastructure which depend of the rewetting conditions.

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Mit Unterstützung der Deutschen Forschungsgemeinschaft.     

The complexity of symbiotic interactions influences the ecological amplitude of the host: A case study in Stereocaulon (lichenized Ascomycota)

Symbiosis plays a fundamental role in nature. Lichens are among the best known, globally distributed symbiotic systems whose ecology is shaped by the requirements of all symbionts forming the holobiont. The widespread lichen‐forming fungal genus Stereocaulon provides a suitable model to study the ecology of microscopic green algal symbionts (i.e., phycobionts) within the lichen symbiosis. We analysed 282 Stereocaulon specimens, collected in diverse habitats worldwide, using the algal ITS rDNA and actin gene sequences and fungal ITS rDNA sequences. Phylogenetic analyses revealed a great diversity among the predominant phycobionts. The algal genus Asterochloris (Trebouxiophyceae) was recovered in most sampled thalli, but two additional genera, Vulcanochloris and Chloroidium, were also found. We used variation‐partitioning analyses to investigate the effects of climatic conditions, substrate/habitat characteristic, spatial distribution and mycobionts on phycobiont distribution. Based on an analogy, we examined the effects of climate, substrate/habitat, spatial distribution and phycobionts on mycobiont distribution. According to our analyses, the distribution of phycobionts is primarily driven by mycobionts and vice versa. Specificity and selectivity of both partners, as well as their ecological requirements and the width of their niches, vary significantly among the species‐level lineages. We demonstrated that species‐level lineages, which accept more symbiotic partners, have wider climatic niches, overlapping with the niches of their partners. Furthermore, the survival of lichens on substrates with high concentrations of heavy metals appears to be supported by their association with toxicity‐tolerant phycobionts. In general, low specificity towards phycobionts allows the host to associate with ecologically diversified algae, thereby broadening its ecological amplitude.     

Über die weite Verbreitung lichenisierter Sippen vonDictyochloropsis und die systematische Stellung vonMyrmecia reticulata (Chlorophyta)

Catinaria grossa is lichenized withDictyochloropsis splendida var.gelatinosa, var. nova. When cultured isolated from the fungus the cells of this variety are covered individually by thick gelatinous envelopes. The phycobionts ofMegalospora gompholoma subsp.gompholoma andM. atrorubicans subsp.australis belong to a new variety ofD. symbiontica, i.e. var.pauciautosporica, which preferentially reproduces by zoo- and aplanospores. The phycobiont ofPseudocyphellaria aurata does not belong toMyrmecia reticulata as formerly thought, but toDictyochloropsis symbiontica. Specimens from one locality in Tenerife and from New Zealand are lichenized with a strain ofD. symbiontica var.symbiontica, those from another locality in Tenerife with a strain ofD. symbiontica var.pauciautosporica. These strains differ in certain characters from other lichenized strains of these varieties.

     

The ultrastructure of the symbionts ofRhizocarpon geographicum,Parmelia conspersa andUmbilicaria pustulata growing under dryness conditions

Summary The dryness-induced ultrastructural changes of both myco- and phycobiont of three lichen species (R. geographicum, P. conspersa, andU. pustulata) have been studied over three months and half, period of time. During this time other ecological factors, such as rock substratum, temperature, light and gas interchange were unaltered compared to the natural conditions. A large number of ultrastructural changes were observed in the mycobiont as well as in the phycobiont (Trebouxia) and often, cells showed a highly disorganized morphology. The most important ultrastructural modifications were: 1. pyrenoglobuli of the algae were peripheral, 2. new and unknown structures were observed in the phycobionts of bothR. geographicum andU. pustulata as well as in the mycobiont of the latter species.     

THE ULTRASTRUCTURE OF LICHENS. I. A GENERAL SURVEY

The fine structure of 10 lichens was examined. A comparison was made of the storage products of the algal symbiont (Trebouxia) in situ in the desiccated and hydrated states of the lichens. All the Trebouxia phycobionts, with the exception of that in Usnea strigosa, had lipid-containing globules in the pyrenoid. The globules were present in both the hydrated and desiccated conditions. Trebouxia in the hydrated condition contained starch granules in the chloroplast as well as the lipid-containing globules in the pyrenoid. The cell wall of Trebouxia consists of an outer electron-dense layer and an inner electron-light layer. Fungal haustoria (in Lecanora rubina) rupture the outer layer of the algal cell wall and invaginate the inner layer. A thick polysaccharide fibrillar material surrounds the fungal cells. Many bacteria were observed within this material. Septa and lomasomes are described. Ellipsoidal bodies, which appear to be an integral and unique part of the lichen fungal ultrastructure, were observed associated with membrane profiles.     

OBSERVATIONS ON LICHENIZED AND FREE-LIVING PHYSOLINUM (CHLOROPHYTA,TRENTEPOHLIACEAE)1

Lichenized Physolinum Printz and free-living Physolinum from a dimly lit cave were studied from fresh collections and cultures, preserved specimens fixed in situ, and cultures that had persisted for 5 years in an environmental chamber. The branched filamentous association consists of a phycobiont and a characteristic ascomycetous mycobiont of one layer that completely ensheathes the algal partner. Epiphytic blue-green algae commonly occur attached to the mycobiont. The phycobiont, Physolinum monilia (De Wildem.) Printz, produces thick-walled, green spiny cells, some of which enlarge and contact the sheathing mycobiont cells; the phycobiont and mycobiont may then develop into new lichenized filaments. The hyaline mycobiont cells extend haustoria bound by the fungus wall deeply into the phycobiont chloroplasts. The epiphytes, Synechocystis-like colonies, are firmly attached to the outer walls of the mycobiont and are associated with several-celled extensions of the fungus beyond the apical phycobiont cells. Free-living Physolinum monilia filaments are branched and moniliform; the search-containing uninucleate cells are spherical to pyriform and have walls of cellulose. Each cell has a single massive chloroplast with plastoglobuli among tightly packed thylakoids. Except for their larger cells, P. monilia filaments appear to be identical to the phycobiont of lichenized Physolinum.     

Survival analyses of symbionts isolated from <Emphasis Type="Italic">Endocarpon pusillum</Emphasis> Hedwig to desiccation and starvation stress

This work deals with the survival analyses of the symbionts isolated from the lichen E. pusillum under desiccation and starvation stress. The mycobiont of the symbionts was under the desiccation in combination with starvation stress, and under starvation stress alone as well. The phycobiont of the symbionts was under desiccation stress alone. The experiments were detected by means of the biomass size, weight and cell density, deformity of the hyphae and cells, and metabolic activity through SEM (scanning electron microscopy), TEM (transmission electron microscopy), FM (fluorescence microscopy), spectrophotometry, and FCM (flow cytometry). The results show that the mycobiont can survive for seven months under desiccation stress in combination with starvation stress, and for eight months under starvation stress alone. The phycobiont can survive for two months under desiccation stress. It can provide a scientific basis for further research of the reproduction biology of lichens and arid desert biocarpet engineering to fix sand and carbon.     

Differential Sensitivity of Lichens to Heavy Metals

Zinc, Cd and Cu inhibited photosynthesis in lichens containingcyanobacterial phycobionts at substantially lower concentrationsthan those causing decreased photosynthesis in lichens containingchlorophycean phycobionts. This distinction was not relatedto differences in total thallus concentrations of Zn, Mg, Caor K or to the quantity of Zn taken up to intracellular sites.When incubated with concentrated Zn solutions the chlorophyceanlichen Cladonia rangiformis accumulated more Zn on extracellularexchangeable sites than did the cyanobacterial lichen Peltigerahorizontalis. algae, cyanobacteria, chlorophyceae, lichens, heavy metal, photosynthetic inhibition, zinc, cadmium, copper, cation uptake     

New and known taxa ofChlorella (Chlorophyceae): Occurrence as lichen phycobionts and observations on living dictyosomes

The algal partner of the lichenPseudocyphellaria carpoloma is a newChlorella species,Chl. sphaerica. It has a saucer- or band-shaped parietal to subparietal chloroplast with a spherical pyrenoid surrounded by a shell of starch. In some of the fully grown cells two dictyosomes lying parallel to each other and changing their position can be observed in the living state. Reproduction occurs by up to 16 autospores. 8 otherPseudocyphellaria species are also lichenized withChlorella phycobionts, apparently belonging toChl. sphaerica. The phycobiont ofWoessia fusarioides belongs toChlorella saccharophila var.ellipsoidea, and to a strain which is morphologically almost identical to one formerly isolated from the lichenTrapelia coarctata. Its ability to gather granules of india ink on the surface of young cells is one of the remarkable characters differentiating it from the latter. In the lichen thallus its cells are regularly penetrated by fungal haustoria.     

Spectral properties of the green alga Trebouxia--a phycobiont of cryptoendolithic lichens in the high-latitude polar regions of Antarctica

An algologically pure culture of the green alga Trebouxia, a phycobiont of cryptoendolithic lichens, was isolated from the sandstone samples collected in the high-altitude polar regions of Antarctica. The absorption and the second-derivative absorption spectra of the acetone extract of the Antarctic phycobiont cells were studied in comparison with those of the Trebouxia phycobiont isolated recently from the Parmeliaceae lichen in the Mid-European climatic zone. The cells of the Antarctic phycobiont were characterized by a lower content of chlorophyll a and a higher ratio of chlorophyll b and carotenoids to chlorophyll a as compared to the Mid-European phycobiont. Furthermore, the carotenoids of the Antarctic phycobiont were more diverse. The low-temperature fluorescence spectra of the Antarctic phycobiont were characterized by an increased intensity of the short-wavelength fluorescence peak of chlorophyll a and a diminished intensity of fluorescence in the long-wavelength spectral region.     

Structural modifications of the phycobiont in the lichen thallus

Summary Modifications in the fine structure of the algal component of two lichens,Aspicilia sp. andSquamarina crassa v.crassa, have been studied. It has been pointed out that fungal penetration is not essential for the mutual relationship between the two symbionts of the lichen thallus. The structural changes taking place during the life cycle of the phycobiont of the two lichens examined are not a response to fungal invasion.Careful examinations of serial sections revealed an interesting correlation between the growth pattern of the thallus and the distribution of the algal cells in the algal layer.Grateful acknowledgement is made to the Israel National Academy of Science for the support of this work.     

The Absorption and Fluorescence Spectra of the Cyanobacterial Phycobionts of Cryptoendolithic Lichens in the High-Polar Regions of Antarctica

The algologically pure cultures of the green–brown cyanobacterium Chroococcidiopsissp. and three cyanobacteria of the genus Gloeocapsa, the blue–green Gloeocapsa sp.₁, the brown Gloeocapsa sp.₂, and the red–orange Gloeocapsa sp.₃, were isolated from sandstones and rock fissures in the high-polar regions of Antarctica. These cyanobacteria are the most widespread phycobionts of cryptoendolithic lichens in these regions. The comparative analysis of the absorption and the second-derivative absorption spectra of the cyanobacteria revealed considerable differences in the content of chlorophyll a and in the content and composition of carotenoids and phycobiliproteins. In addition to phycocyanin, allophycocyanin, and allophycocyanin B, which were present in all of the cyanobacteria studied, Gloeocapsa sp.₂ also contained phycoerythrocyanin and Gloeocapsa sp.₃ phycoerythrocyanin and C-phycoerythrin (the latter pigment is typical of nitrogen-fixing cyanobacteria). The fluorescence spectra of Gloeocapsa sp.₂ and Gloeocapsa sp.₃ considerably differed from the fluorescence spectra of the other cyanobacteria as well. The data obtained suggest that various zones of the lichens may be dominated either by photoheterotrophic or photoautotrophic cyanobacterial phycobionts, which differ in the content and composition of photosynthetic pigments.