Graphene and its derivatives are heralded as “miracle” materials with manifold applications in different sectors of society from electronics to energy storage to medicine. The increasing exploitation of graphene-based materials (GBMs) necessitates a comprehensive evaluation of the potential impact of these materials on human health and the environment. Here, we discuss synthesis and characterization of GBMs as well as human and environmental hazard assessment of GBMs using in vitro and in vivo model systems with the aim to understand the properties that underlie the biological effects of these materials; not all GBMs are alike, and it is essential that we disentangle the structure–activity relationships for this class of materials.
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.
Phytohormones are pivotal signaling compounds in higher plants, in which they exert their roles intracellularly, but are also released for cell-to-cell communication. In unicellular organisms, extracellularly released phytohormones can be involved in chemical crosstalk with other organisms. However, compared to higher plants, hardly any knowledge is available on the roles of phytohormones in green algae. Here, we studied phytohormone composition and extracellular release in aero-terrestrial Trebouxiophyceae. We investigated (a) which phytohormones are produced and if they are released extracellularly, and if extracellular phytohormone levels are (b) affected by environmental stimuli, and (c) differ between lichen-forming and non-lichen-forming species. Three free-living microalgae (Apatococcus lobatus, Chloroidium ellipsoideum, and Myrmecia bisecta) and three lichen-forming microalgae (Asterochloris glomerata, Trebouxia decolorans, and Trebouxia sp.) were studied. Algae were grown on solid media and the following cellular phytohormones were identified by ultra-high-performance liquid chromatography coupled with tandem mass spectrometry (UHPLC-MS/MS): indole-3-acetic acid (IAA), indole-3-butyric acid (IBA), abscisic acid (ABA), gibberellin A 4 (GA 4), and zeatin (ZT). Furthermore, IAA, IBA, ABA, jasmonic acid (JA), gibberellin A 3 (GA 3), and GA 4 were found to be released extracellularly. IAA and ABA were released by all six species, and IAA was the most concentrated. Phytohormone release was affected by light and water availability, especially IAA in A. glomerata, Trebouxia sp., and C. ellipsoideum. No clear patterns were observed between lichen-forming and non-lichen-forming species. The results are envisaged to contribute valuable baseline information for further studies into the roles of phytohormones in microalgae.
A lichen transplant study aimed at investigating a strong increase in mercury concentrations in lichens was run in a territory of NE Italy where background values were very low only 8 years before. Thalli of the lichen Pseudevernia furfuracea collected in a pristine area were exposed for 1.5, 3 and 6 months at 31 sites selected according to the observed pattern of Hg concentrations, location of the suspected source (a new waste incinerator) and prevailing wind direction. Hg strongly increased at eight sites after 1.5 months, at 12 after 3 months and at 20 after 6 months. The highest values were always located SW and S of the incinerator, in good agreement with the prevailing night wind direction. It was concluded that, although the immediate risk for the population living close to the incinerator is low, long-term hazard due to Hg accumulation in the surrounding environment should be seriously taken into account.
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