Desiccation tolerance and lichenization: a case study with the aeroterrestrial microalga Trebouxia sp. (Chlorophyta)

Coccoid algae in the Trebouxia genus are the most common photobionts of chlorolichens but are only sporadically found in soil or bark outside of a lichen. They all appear to be desiccation tolerant, i.e. they can survive drying to water contents of below 10 %. However, little is known about their longevity in the dry state and to which extent lichenization can influence it. Here, we studied the longevity in the dry state of the lichenized alga (LT) Trebouxia sp. in the lichen Parmotrema perlatum, in comparison with axenically grown cultures (CT) isolated from the same lichen. We report on chlorophyll fluorescence emission and reactive oxygen species (ROS) production before desiccation, after 15\u201345 days in the dry state under different combinations of light and air humidity and after recovery for 1 or 3 days in fully hydrated conditions. Both the CT and the LT were able to withstand desiccation under high light (120 lmol photons m-2 s-1 for 14 h per day), but upon recovery after 45 days in the dry state the performance of the CT was better than that of the LT. By contrast, the quenching of excess light energy was more efficient in the LT, at high relative humidities especially. ROS production in the LT was influenced mostly by light exposure, whereas the CT showed an oxidative burst independent of the light conditions. Although lichenization provides benefits that are essential for the survival of the photobiont in high-light habitats, Trebouxia sp. can withstand protracted periods of photo-oxidative stress even outside of a lichen thallus

Considerazioni preliminari su una possibile nuova Pterygiopsis trovata in Puglia

La famiglia delle Lichinaceae comprende generi di licheni crostosi con morfologie e fotobionti molto diversi, alcuni dei quali sono particolarmente controversi e problematici. In genere si tratta di organismi pionieri tolleranti forti stress ambientali, che vivono su suoli minerali e pareti rocciose con percolamento d\u2019acqua, in ambienti caratterizzati in genere da elevato irraggiamento. Pterygiopsis \ue8 un genere di una ventina di licheni prevalentemente epilitici, con habitus da crostoso a sub-squamuloso umbilicato, di difficile identificazione. Alcune specie sono note solo per il materiale tipo e la loro interpretazione \ue8 molto problematica. Per l\u2019Italia \ue8 nota un\u2019unica specie, Pterygiopsis affinis Massal., che \ue8 relativamente frequente su affioramenti calcarei e dolomitici e si caratterizza per avere un tallo placodioide e aschi polispori, con spore da ellissoidali a subsferiche. Alcuni anni fa in Puglia era stata raccolta una Pterygiopsis evidentemente molto prossima a P. affinis, ma con superficie evidentemente sorediata e tallo nettamente pi\uf9 robusto. Per poter interpretare la sua posizione tassonomica si \ue8 iniziato uno studio critico dell\u2019intero genere. Per ogni taxon noto in letteratura \ue8 stata recuperata la diagnosi originale, che \ue8 stata integrata con le descrizioni fornite in Flore e opere monografiche. \uc8 stata quindi costruita una matrice \u201ctaxa/caratteri\u201d, con l\u2019obiettivo di produrre una chiave di identificazione. Nel frattempo sono in corso dei campionamenti nella regione pugliese per cercare di reperire ulteriori popolazioni del taxon sorediato, al fine di verificare se i caratteri morfologici osservati nella ricca collezione originale sono costantemente espressi

Seasonal variations of PAHs content and distribution patterns in a mixed land use area: A case study in NE Italy with the transplanted lichen Pseudevernia furfuracea

The seasonal differences of the polycyclic aromatic hydrocarbons (PAHs) content in lichen transplants were investigated in an area of ca. 40 square kilometers in NE Italy characterized by different land use. Two sets of samples of the epiphytic lichen Pseudevernia furfuracea were collected in a pristine area of the Carnic Alps and transplanted to 40 exposure sites for a period of two months, respectively in late winter and in summer. Results revealed a pronounced difference between the two seasons in terms of PAH content and distribution patterns. After the summer exposure the PAH concentrations in the transplants were more than one order of magnitude lower than after the winter exposure (ranging from 48.22 to 272.73 ng g 121 dw and from 289.73 to 1575.85 ng g 121 dw in the summer and winter samples respectively). Also the main emission sources changed, mostly due to the drastic reduction in the emissions by wood burning for domestic heating and to the different meteorological conditions. In summer PAHs degradation was enhanced by intense UV radiation, high temperatures, and presence of ozone. The implications of these findings for the biomonitoring of PAHs pollution are addressed

Interactions of airborne graphene oxides with the sexual reproduction of a model plant: When production impurities matter

The increasing use of graphene-related materials (GRMs) in everyday-life products raises concerns for their possible release into the environment and consequent impact on organisms. GRMs have widely varying effects on plants and, according to recent evidences, graphene oxide (GO) has the potential to interfere with the sexual reproduction owing to its acidic properties and production residues. Here, stigmas of the model plant Cucurbita pepo (summer squash) were subjected to simulated dry depositions of GO and GO purified from production residues (PGO). Stigmas were then hand-pollinated and GRM deposition was checked by ESEM and confocal microscopy. Analysis of stigma integrity, pH homeostasis and pollen-stigma interactions did not reveal negative effects. Fruit and seed production were not affected, but GO depositions of 22.1 ± 7.2 ng mm-2 affected the normal development of seeds, decreasing seed dimensions, seed germination and germination speed. The elemental analysis revealed that GO has significant quantities of production residues, such as strong acids and oxidants, while PGO has only traces, which justifies the differences observed in the effects caused by the two materials. Our results show that GO depositions of up to 11.1 ± 3.6 ng mm-2, which fall within the variation range of total dry particulate matter depositions reported in the literature, are safe for reproduction of C. pepo. This is the first "safety" limit ever recorded for depositions of "out-of-the-box" GO concerning the reproduction of a seed plant. If confirmed for wind-pollinated species, it might be considered for policymaking of GRMs emissions in the air

Graphene oxide impairs the pollen performance of Nicotiana tabacum and Corylus avellana suggesting potential negative effects on the sexual reproduction of seed plants

The production of graphene based materials (GBMs) is steadily increasing but the effects of the possible release of GBMs in the environment are far from being understood. Graphene oxide (GO) is among the most active GBMs and it causes widely varying effects on the vegetative body of seed plants. However, nothing is known yet about its potential effects on the reproductive process. This study addresses the effects of GO on pollen germination and pollen tube elongation in the model species Nicotiana tabacum and in the non-model species Corylus avellana. In vitro germination experiments were conducted without or with GO (control and treated samples, respectively) at concentrations of 25, 50 and 100 μg mL−1. Pollen germination and tube elongation were affected at GO concentrations ≥50 μg mL−1, decreasing by 20% and 19% in N. tabacum and by 68% and 58% in C. avellana, respectively. GO did not affect the viability of N. tabacum pollen, but doubled the frequency of bent tubes. Microscopy observations of pollen tubes exposed to a cellpermeant, dual-excitation ratiometric pH indicator revealed that GO affected the intracellular pH homeostasis. Further germination experiments on C. avellana conducted by inverting the pH conditions of the control and treated (100 μg GO mL−1) samples demonstrated that the main factor influencing the pollen performance is the acidic properties of GO. This might affect the reproductive process of numerous seed plants thus being relevant from an environmental point of view

New features of desiccation tolerance in the lichen photobiont Trebouxia gelatinosa are revealed by a transcriptomic approach.

Trebouxia is the most common lichen-forming genus of aero-terrestrial green algae and all its species are desiccation tolerant (DT). The molecular bases of this remarkable adaptation are, however, still largely unknown. We applied a transcriptomic approach to a common member of the genus, T. gelatinosa, to investigate the alteration of gene expression occurring after dehydration and subsequent rehydration in comparison to cells kept constantly hydrated. We sequenced, de novo assembled and annotated the transcriptome of axenically cultured T. gelatinosa by using Illumina sequencing technology. We tracked the expression profiles of over 13,000 protein-coding transcripts. During the dehydration/rehydration cycle c. 92 % of the total protein-coding transcripts displayed a stable expression, suggesting that the desiccation tolerance of T. gelatinosa mostly relies on constitutive mechanisms. Dehydration and rehydration affected mainly the gene expression for components of the photosynthetic apparatus, the ROS-scavenging system, Heat Shock Proteins, aquaporins, expansins, and desiccation related proteins (DRPs), which are highly diversified in T. gelatinosa, whereas Late Embryogenesis Abundant Proteins were not affected. Only some of these phenomena were previously observed in other DT green algae, bryophytes and resurrection plants, other traits being distinctive of T. gelatinosa, and perhaps related to its symbiotic lifestyle. Finally, the phylogenetic inference extended to DRPs of other chlorophytes, embryophytes and bacteria clearly pointed out that DRPs of chlorophytes are not orthologous to those of embryophytes: some of them were likely acquired through horizontal gene transfer from extremophile bacteria which live in symbiosis within the lichen thallus

Graphene oxide degradation by a white-rot fungus occurs in spite of lignin peroxidase inhibition

This study investigated the degradation of graphene oxide (GO) by the white-rot fungus Phanerochaete chrysosporium. Axenic fungal suspensions were inoculated in malt extract glucose medium enriched with various concentrations of GO and allowed to grow for several months. Biomass, pH, H2O2 content and activity of laccase (Lac) and lignin peroxidase (LiP) in the culture media were monitored, along with the physicochemical changes of GO over time followed by TEM, Raman, XPS and TGA. Lower concentrations of GO exhibited a stronger stimulating effect on P. chrysosporium growth and the production of Lac and H2O2 compared to higher concentrations, probably due to an excessive parallel increase in GO degradation by-products. The fungus significantly altered the structure of GO, with increase in the Raman D band, although GO neutralized LiP activity, possibly by unspecific adsorption. The activity of isolated LiP, but not of Lac, was suppressed in the presence of GO. Moreover, Lac caused modifications in the GO lattice as evidenced by a significant increase in the ratio between the intensity of the D and G bands of the Raman spectra. This enzyme emerges as a key player in the biodegradation of GRMs within terrestrial ecosystems, as its release extends beyond fungi to several other microorganisms