Fine structure of the vegetative thallus of the lichen,Peltigera polydactyla

Summary An investigation was made of the vegetative thallus of the lichen Peltigera polydactyla. Using a modified embedding technique it was shown that the ultrastructure of the mycobiont was not radically different from that of nonlichenized Discomycetes, and that the ultrastructure of the phycobiont was like that of the blue-green alga Nostoc. In addition to what were considered healthy blue-green algal cells other cells were present which obviously were breaking down. Well defined heterocysts were also present. No haustoria were found in the thallus.     

Bioactivity of secondary metabolites and thallus extracts from lichen fungi

Fungal secondary compounds and total extracts are known to affect growth of bacteria, fungi, and plants. This study tested the effects of purified compounds and total extracts from three lichens on the growth of two plant pathogens, Ophiostoma novo-ulmi ssp. americana and Sclerotinia sclerotiorum. Usnic acid showed no reduction in relative growth rates (RGR), whereas vulpinic acid reduced RGR for both fungi and atranorin reduced RGR of S. sclerotiorum only. However, purified vulpinic acid showed stronger effects than total extracts on fungal growth. The results suggest that these lichens show further promise as a source for bioactive compounds against fungi.     

Identification of crystalline material found in the thallus of the lichen, Myelochroa leucotyliza

Lichens are symbiotic associations of fungi and algae (or cyanobacteria). Fungal cells produce large amounts of lipid, assisted by algae, and secrete them out of the cells. Some of the secreted lipids crystallize in the thallus of the lichen. The crystalline materials sometimes occupy 30% of total dry weight of the thallus. This unusual amount of lipid crystal led to our interest in investigating the mechanism of lipid secretion. To begin the cell biological study of lipid secretion and to know the significance of the existence of such crystals in the thallus, it is essential to identify the crystal. The lipid crystal extracted from the thallus of a lichen, Myelochroa leucotyliza, was studied by EM observations, TLC analysis, and EM and X-ray diffraction methods. Atranorin is the predominant component of the crystalline materials in the lipids extracted.     

A feeling for the superorganism: expression of plant form in the lichen thallus

The composite thalli produced by lichen fungi in symbiosis with algae often show structural convergences with plants. Similar overall thallus forms and branching patterns may arise in lichens with very different anatomical construction, indicating the autonomy of the morphological level of organization. Fungal and algal growth and division may be highly integrated within meristem-like morphogenetic zones in many lichens, whereas in others the symbionts may contribute in a less synchronized fashion to the construction of the thallus. Although thallus-level morphology and morphogenesis may be compared with those of plants, ontogeny of the lichen thallus differs fundamentally. Observations of lichen ontogeny illustrate the formation of the thallus by unification of autonomous, primary cellular elements in co-ordinated growth. In land plants and many algae, by contrast, the plant body is the primary structure, the cellular elements of which represent secondary subdivisions. The convergences in form are based on a common mode of nutrition in combination with cell-wall building materials that impart similar structural potential. The photosynthetic apparatus forming the basis of this mode of nutrition is not a convergent feature, however, but a homologous structure that originated in the cyanobacteria and subsequently passed laterally into diverse biological lineages by repeated endosymbioses. With consolidation of these symbioses as eukaryotic algae and plants, the organismal level of organization was repeatedly re-established with increasing degrees of complexity, and morphological convergences were expressed at these new levels. In lichens, by contrast, the symbiosis is not organismally consolidated; morphological expression instead emerges at the superorganismal level.  © 2006 The Linnean Society of London, Botanical Journal of the Linnean Society , 2006, 150 , 89–99.     

石果衣菌藻次级代谢产物的初步研究

荒漠地衣石果衣 Endocarpon pusillum中未能检测出任何次级代谢产物,然而,其共生菌基因组中却含有14个PKS基因和2个NRPS基因。通过激活培养后从中分离出3个次级代谢产物,4,6,9-三羟基-7-甲基-1H,3H-萘并[1,8-cd]吡喃-1,3-二酮（lamellicolic anhydride）、石果衣菌素A（endocarpin A）及石果衣菌素B（endocarpin B）,后二者为新结构化合物。从其共生藻柯氏复球藻 Diplosphaera chodatii中分离出3个脱镁叶绿素类化合物,即脱镁叶绿素甲酯酸b（phaeophorbide b）、13-表-脱镁叶绿素甲酯酸a（13- epi-phaeophorbide a）及脱镁叶绿素甲酯酸a（phaeophorbide a）。其中脱镁叶绿素甲酯酸b具有中等的清除DPPH活性。     

33P translocation in the thallus of the mat-forming lichen Cladonia portentosa

The extent of vertical migration of ³³P in thalli of the heathland lichen Cladonia portentosa was investigated under field conditions. ³³P-labelled orthophosphate was introduced into the bottom 25 mm of podetia cut to a length of 50 mm from the apices. The distribution of label was scanned using a molecular imager immediately after incubation, and after growing for 8 wk and 6 months. Differences in the relative distribution of label between podetia harvested at the beginning and the end of the experiment showed that there had been a significant migration of ³³P upwards out of the labelled 25 mm stratum towards the apex. This was confirmed by statistically significant changes in the median (md) and the 90 percentile of total relative distribution of ³³P label. In a control treatment in which label was introduced into the apical 25 mm of podetia, which were then grown inverted (top down), no upward movement of label was detected. By contrast, a statistically significant reduction in the md of the distribution indicated migration downwards towards the thallus apex. The results are consistent with the hypothesis that P is recycled within podetia of mat-forming lichens, migrating from degrading basal regions upwards to the growing apices following a source–sink relationship.     

The significance of thallus size for the water economy of the cyanobacterial old-forest lichen Degelia plumbea

Rosette-formed, circular thalli of Degelia plumbea were studied in the laboratory. Regardless of thallus size, the optimal quantum yield of photosystem II (F _V/F _M) remained at a high, constant level during a drying cycle starting with fully hydrated thalli until the thallus water content reached about 200%. Net photosynthesis reached a maximum level at this hydration level. Thereafter, both F _V/F _M and net photosynthesis fell rapidly to zero at a water content of somewhat less than 100%. There was a highly significant, positive relationship between thallus size and the water-holding capacity, as well as a strong, negative correlation between size and water loss per thallus area. Consequently, an increase in thallus size from 1 to 36 cm² lead to a tenfold prolongation of the photosynthetically active period during a drying cycle at a low radiation regime. The improved water-holding capacity in larger thalli is mainly a result of a thicker hypothallus. The fast desiccation of small thalli suggests that the regeneration of D. plumbea could be severely hampered by nearby logging that raises the evaporative demand by increasing radiation loads and wind exposure at remaining lichen sites. Received: 12 December 1997 / Accepted: 20 March 1998     

Toxic effects of the thallus of the lichen Cladonia foliacea on the growth and morphogenesis of bryophytes

In this paper the effects induced by the whole thallus of the lichen Cladonia foliacea on the growth and development of some mosses (Funaria hygrometrica, Bryum dunense, Pleurochaete squarrosa) and the liverwort Lunularia cruciata, have been studied. The main effects induced by Cladonia thalli during periods of co-existence in vitro with gametophytes is a delay in the regeneration of new filaments asssociated with the inhibition of their growth together with a global decrement in the number of gametophores. Other alterations at cytoplasm level are a granular appearance of cytoplasm and many microvesicles in the newly-regenerated filaments, enlarged periplasmic space and changes in chloroplast shape. Current results are compared to previous data obtained with pure substances isolated from C. foliacea thalli.     

Trouble with lichen: the re-evaluation and re-interpretation of thallus form and fruit body types in the molecular era

Following discussions of the definition of the terms ‘lichen’ and ‘thallus’, the role of lichenization in the evolution of asco- and basidiomycetes, and divergence and convergence in fruit body types, the morphogenetic interpretation of types of thallus form in lichens is reviewed. Attention is drawn to the various morphogenetic hypotheses proposed to explain the lichen thallus, but it is concluded that it is best interpreted as a novel phenotype with no exact homologue. Similar ascomatal and thallus types are found in lichen-forming fungi of different orders and families, as now revealed by molecular phylogenetic studies. These are interpreted as examples of convergent evolution, strategies by which unrelated fungi either display captured algae to maximize photosynthetic opportunities, or to attach themselves to a substratum. Phenotypic evolution of fruit body and thallus types in the major orders and clades is summarized, and the thallus types known in each order are tabulated. An hypothesis relating the evolution of these structures to hygroscopic movements is proposed, and the critical position of lichens in developing an integrated approach to ascomycete evolution is emphasized.     

Starting from scratch: Evolution of the lichen thallus in the basidiolichen Dictyonema (Agaricales: Hygrophoraceae)

Phylogenetic studies indicate that the basidiolichen genus Dictyonema s.lat., often thought to represent only a single genus with few species, includes several well-supported genus-level clades, all of which form associations with a unique lineage of obligately lichenized cyanobacteria (Rhizonema). In an attempt to elucidate the evolution and genus- and species-level diversification in Dictyonema s.lat., we generated 68 new sequences of the nuclear large subunit rDNA (nuLSU), the internal transcribed spacer (ITS), and the RNA polymerase II subunit (RPB2), for 29 species-level lineages representing all major clades of Dictyonema s.lat. and most of the species currently known. The multilocus phylogeny obtained via maximum likelihood and Bayesian approaches indicates the presence of five genus-level groups: a basal clade, Cyphellostereum, that is sister to the rest of the species, a paraphyletic grade representing Dictyonema s.str., and three clades representing the genera Acantholichen, Cora, and Corella. To determine the evolutionary transformations of the lichenized thallus in the group, ancestral character state reconstruction was done using six characters (lichenisation, thallus type, cortex type, hyphal sheath and haustorial type, photobiont morphology, and basidiocarp type). Our analysis indicates a progressive development of the lichenized thallus from loosely organized filamentous crusts with separate, cyphelloid basidiocarps in Cyphellostereum, to filamentous crusts with derived hyphal sheath and cyphelloid–stereoid basidiocarps partially incorporated into the lichen thallus in Dictyonema, to squamulose–foliose thalli with corticioid basidiocarps entirely supported by the lichen thallus in Cora. These results indicate a remarkable evolutionary integration of lichenized and reproductive tissues in Dictyonema s.lat., supporting the hypothesis that, at least in this case, lichenized thalli may have evolved from reproductive structures in their nonlichenized ancestors.     

Wind-acclimated thallus morphogenesis in a lichen (Evernia prunastri, Parmeliaceae) probably favored by grazing

How does the morphogenesis of a widespread epiphytic lichen interact with the environment, leading to amazingly polymorphic and wind-tolerant fruticose thalli? A series of photographs showed that the normal branches were basically even and flat with isotomic-dichotomous branchings. Numerous deviations from this basic regular pattern were found and traced back to their origins in the asymmetry of the branches’ cross sections. This was observed quantitatively (statistically testable) in the field, while the thalli were growing. This large variability in growth of single branches was a prerequisite for the polymorphism seen in complete thallus growth forms. The structure and distribution of the mentioned important asymmetries in branch cross sections can best be explained by the effect of grazing on cortex and phycobiont layer. Very small-scale growth observations and experimental simulation confirmed this. In thalli with many such small-scale variations in branch growth the overall thallus growth form became wind acclimated as a result of the selective effect of wind exposure on the thallus phenotype: branches growing windwardly grew more slowly. Such thalli were well protected from being dislodged by wind, and they desiccate slowly as demonstrated by a previous study.     

CO2 exchange and thallus nitrogen across 75 contrasting lichen associations from different climate zones

Aiming to investigate whether a carbon-to-nitrogen equilibrium model describes resource allocation in lichens, net photosynthesis (NP), respiration (R), concentrations of nitrogen (N), chlorophyll (Chl), chitin and ergosterol were investigated in 75 different lichen associations collected in Antarctica, Arctic Canada, boreal Sweden, and temperate/subtropical forests of Tenerife, South Africa and Japan. The lichens had various morphologies and represented seven photobiont and 41 mycobiont genera. Chl a, chitin and ergosterol were used as indirect markers of photobiont activity, fungal biomass and fungal respiration, respectively. The lichens were divided into three groups according to photobiont: (1) species with green algae, (2) species with cyanobacteria, and (3) tripartite species with green algal photobionts and cyanobacteria in cephalodia. Across species, thallus N concentration ranged from 1 to 50 mg g^-1 dry wt., NP varied 50-fold, and R 10-fold. In average, green algal lichens had the lowest, cyanobacterial Nostoc lichens the highest and tripartite lichens intermediate N concentrations. All three markers increased with thallus N concentration, and lichens with the highest Chl a and N concentrations had the highest rates of both P and R. Chl a alone accounted for ca. 30% of variation in NP and R across species. On average, the photosynthetic efficiency quotient [K_F=(NP_max+R)/R)] ranged from 2.4 to 8.6, being higher in fruticose green algal lichens than in foliose Nostoc lichens. The former group invested more N in Chl a and this trait increased NP_max while decreasing R. In general terms, the investigated lichens invested N resources such that their maximal C input capacity matched their respiratory C demand around a similar (positive) equilibrium across species. However, it is not clear how this apparent optimisation of resource use is regulated in these symbiotic organisms.     

Structural modifications of nucleosides in ionic liquids

Nucleoside chemistry represents an important research area for drug discovery, as many nucleoside analogs are prominent drugs and have been widely applied for cancer and viral chemotherapy. However, the synthesis of modified nucleosides presents a major challenge, which is further aggravated by poor solubility of these compounds in common organic solvents. Most of the currently available methods for nucleoside modification employ toxic high boiling solvents; require long reaction time and tedious workup methods. As such, there is constant effort to develop process chemistry in alternative medium to limit the use of organic solvents that are hazardous to the environment and can be deleterious to human health. One such approach is to use ionic liquids, which are ‘designer materials’ with unique and tunable physico-chemical properties. Studies have shown that methodologies using ionic liquids are highly efficient and convenient for the synthesis of nucleoside analogs, as demonstrated by the preparation of pharmaceutically important anti-viral drugs. This article summarizes recent efforts on nucleoside modification using ionic liquids.     

Development of thallus axes in Usnea longissima (Parmeliaceae, Ascomycota), a fruticose lichen showing diffuse growth

? Premise of the study: While cell wall thickening in plants is generally associated with tissue maturation, fungal tissues in at least two lichens continue to grow extensively while accumulating massively thickened cell walls. We examined Usnea longissima to determine how diffuse growth shapes morphological and anatomical development of thallus axes and how the highly thickened cell walls of the central cord behave in diffuse growth. ? Methods: Fresh material was examined with light and epifluorescence microscopy and conventional and low-temperature SEM. Fixed material was embedded in Spurr's resin, microtome-sectioned, and examined with TEM and light microscopy. ? Key results: Main axes consisted essentially of bare medullary cord tissue; their characteristic morphology developed by destruction of the overlying cortex and consequent stimulation of lateral branch formation. Fungal cells of the cord tissue continually deposited wall layers of electron-transparent substances and layered, electron-dense materials that include UV-epifluorescent components. Discontinuities were evident in the outermost layers; new branch cells grew through wall materials accumulated by older neighboring cells. ? Conclusions: Sustained diffuse growth of cord tissue in U. longissima underlies the structural transformation of a corticated thallus branch into a long axis. In the cord tissue, diffuse growth may be responsible for the increasingly disrupted appearance of the older, electron-dense cell wall layers, while new wall materials are laid down adjacent to the protoplast. Cell and tissue development appeared comparable to that observed previously in Ramalina menziesii, although accumulation of wall material was somewhat less extensive and with a greater proportion of electron-dense/UV-epifluorescent components.     

Reiterative production and deformation of cell walls in expanding thallus nets of the lichen ramalina menziesii (Lecanorales,Ascomycetes)

The thallus of the lichen Ramalina menziesii Tayl. is composed of net-like units that develop by diffuse expansion of perforated tissue produced at the net apex. Study of net tissue with transmission electron microscopy reveals that the cortical cells are surrounded by a succession of cell walls alternating with layers of an electron-transparent matrix substance. In the course of thallus growth the cortical cell walls are continually deformed and new ones constructed. The deposition of new walls and matrix layers displaces the older walls centrifugally from the cell. Electron-dense boundaries develop at the interfaces among cells where the remains of the oldest walls are compressed against those of neighboring cells. As new branch cells are inserted through the concentric accumulations, the dense boundaries appear to enclose fascicles of cells, visible in cross section with light microscopy. Cortical organization in Ramalina menziesii is contrasted with that reported in other lichens, and a functional relationship to diffuse growth of the thallus is suggested.     

Light might regulate divergently depside and depsidone accumulation in the lichen Parmotrema hypotropum by affecting thallus temperature and water potential

Depsides and depsidones are the most common secondary products uniquely produced in lichens by the fungal symbiont, and they accumulate on the outer surface of its hyphae. Their biological roles are subject to debate. Quantitatively the compounds typical of a given lichen can vary dramatically from thallus to thallus. Several studies have addressed whether this variability is correlated with the light reaching different thalli, but the conclusions are contradictory. We addressed the question with the lichen Parmotrema hypotropum growing on unshaded, vertical tree trunks, a controlled natural environment where the light absorbed by each thallus over its lifetime is the only major position-dependent variable. The exact north-east-south-west orientation of each thallus was used to calculate its yearly light exposure based on astronomical and meteorological considerations. The calculated irradiation around the trunk, distributed over a continuous 40-fold intensity range, then was compared with the amount of compound per unit thallus weight, determined by quantitative thin layer chromatography. P. hypotropum accumulates the depside atranorin in the cortex and the depsidone norstictic acid in the medulla and around the algae. A direct correlation was observed between the yearly amount of light reaching the lichen and the amount of atranorin. In contrast, the amount of norstictic acid decreased with increasing light. Although we did not measure thallus temperature and water potential, a unifying interpretation of these and other published data is that depside/depsidone accumulation in lichens is mediated by localized changes in temperature and water potential produced by light absorption within each thallus. This suggests water relations-based functions for depsides and depsidones.     

Structural cooperativity in histone H3 tail modifications

Post-translational modifications of histone H3 tails have crucial roles in regulation of cellular processes. There is cross-regulation between the modifications of K4, K9, and K14 residues. The modifications on these residues drastically promote or inhibit each other. In this work, we studied the structural changes of the histone H3 tail originating from the three most important modifications; tri-methylation of K4 and K9, and acetylation of K14. We performed extensive molecular dynamics simulations of four types of H3 tails: (i) the unmodified H3 tail having no chemical modification on the residues, (ii) the tri-methylated lysine 4 and lysine 9 H3 tail (K4me3K9me3), (iii) the tri-methylated lysine 4 and acetylated lysine 14 H3 tail (K4me3K14ace), and (iv) tri-methylated lysine 9 and acetylated lysine 14 H3 tail (K9me3K14ace). Here, we report the effects of K4, K9, and K14 modifications on the backbone torsion angles and relate these changes to the recognition and binding of histone modifying enzymes. According to the Ramachandran plot analysis; (i) the dihedral angles of K4 residue are significantly affected by the addition of three methyl groups on this residue regardless of the second modification, (ii) the dihedral angle values of K9 residue are similarly altered majorly by the tri-methylation of K4 residue, (iii) different combinations of modifications (tri-methylation of K4 and K9, and acetylation of K14) have different influences on phi and psi values of K14 residue. Finally, we discuss the consequences of these results on the binding modes and specificity of the histone modifying enzymes such as DIM-5, GCN5, and JMJD2A.     

Caloplaca erodens [sect. Pyrenodesmia], a new lichen species from Italy with an unusual thallus type

Caloplaca erodens is a new species of sect. Pyrenodesmia, characterised by an orbicular, sorediate, bluish-grey thallus which is endolithic but emerges at the periphery with a white, K−, obscurely lobate prothallus. The species is frequent on calcareous outcrops and walls of isolated churches and ruins of the Central Apennines (Sibillini, Gran Sasso), where it may occur in large monospecific populations, from 1000 to 2500 m asl., and is also known from dry sites of the southern Alps. It has been found with apothecia only in the type locality, being predominantly sterile. The reproduction of this lichen is evidently linked to the release of fragments of clusters of photobiont cells and mycobiont hyphae which are continuously exposed with the dissolution of the substratum. Readily distinguished from the apparently similar endolithic C. alociza (which is characterised by numerous apothecia, black, K+ purple prothallus, and esorediate thallus), C. erodens probably belongs to the C. circumalbata complex, whose taxa are always epilithic but have a white, K− prothallus. The phylogenetic position of the new species within sect. Pyrenodesmia as inferred by ITS sequences of the nuclear ribosomal DNA is shortly discussed.     

Distribution of histamine in the thallus ofFurcellaria lumbricalis

Histamine occurs in all regions of the thallus of male, female and tetrasporophyte plants ofFurcellaria lumbricalis (Huds.) Lamour. The mean values varied from 60 μg to 500 μg (g fresh weight)^?1. There were few consistent differences either between the same region of different types of plant or different regions of the thallus of one type of plant. Fluorescence staining of sections of the thalli ofF. lumbricalis, with o-phthalaldehyde, revealed that cells of the cortex and medulla have histamine associated with them. The histamine appears to be intracellular since only intact cells exhibit fluorescence. Cells in sections of female plants ofPolyides rotundus (Huds.) Grev., which do not contain histamine, do not exhibit fluorescence dependent upon o-phthalaldehyde.