A huge amount of studies highlighted the importance of high ascorbic acid (AA) content in ozone tolerance, yet the relationship between them appears more complex than a simple direct correlation. Sometimes the connection is clear, for example, two Arabidopsis mutants defective in the main AA biosynthetic pathway (vtc mutants) were identified by means of their ozone sensitivity. However, some low-AA containing mutants are relatively tolerant, suggesting that AA location/availability could be more relevant than total content. A clear distinction should also be made between ozone tolerance obtained when AA content is increased by experimental supplementation (exogenous AA), and the physiological role of plant-synthesized AA (endogenous AA), whose amount is apparently subjected to tight regulation. Recent findings about the role of AA in signal transduction and epigenetic regulation of gene expression open new routes to further research.

In the present work, we investigated the response to Cd in Leptodictyum riparium, a cosmopolitan moss (Bryophyta) that can accumulate higher amounts of metals than other plants, even angiosperms, with absence or slight apparent damage. High-performance liquid chromatography followed by electrospray ionization tandem mass spectrometry of extracts from L. riparium gametophytes, exposed to 0, 36 and 360 µM Cd for 7 days, revealed the presence of γ-glutamylcysteine (γ-EC), reduced glutathione (GSH), and traces of phytochelatins. The increase in Cd concentrations progressively augmented reactive oxygen species levels, with activation of both antioxidant (catalase and superoxide dismutase) and detoxifying (glutathione-S-transferase) enzymes. After Cd treatment, cytosolic and vacuolar localization of thiol peptides was performed by means of the fluorescent dye monochlorobimane and subsequent observation with confocal laser scanning microscopy. The cytosolic fluorescence observed with the highest Cd concentrations was also consistent with the formation of γ-EC-bimane in the cytosol, possibly catalyzed by the peptidase activity of the L. riparium phytochelatin synthase. On the whole, activation of phytochelatin synthase and glutathione-S-transferase, but minimally phytochelatin synthesis, play a role to counteract Cd toxicity in L. riparium, in this manner minimizing the cellular damage caused by the metal. This study strengthens previous investigations on the L. riparium ability to efficiently hinder metal pollution, hinting at a potential use for biomonitoring and phytoremediation purposes.

It is well-known that atmospheric pollution, first and foremost the particulate matter (PM), causes serious diseases in humans. China’s metropolises and Italy’s Po Valley have in fact achieved a concerning degree of notoriety thanks to runaway air pollution problems. The spread of viral respiratory diseases is facilitated in polluted environments, an example of which is the respiratory syncytial virus bronchiolitis. In this opinion paper, we consider the possible relationship between air pollution, primarily airborne PM10–2.5, and the spread of the novel coronavirus in Northern Italy. If it is true that the novel coronavirus remains active from some hours to several days on various surfaces, it is logical to postulate that the same can occur when it is adsorbed or absorbed by the atmospheric particulate matter, which may also help carry the virus into the human respiratory system. As the Earth presents us with a very high bill to pay, governments and other authorities need to take prompt action to counter excessive pollution levels, both in Italy and in other countries.

Plant phytochelatin synthases undergo evolutionarily rapid functional differentiation after duplication, allowing fast and precise adjustment of metal detoxification capacity by modulation of both transcription and enzymatic activity.

Phytochelatin synthases (PCSs) play essential roles in detoxification of a broad range of heavy metals in plants and other organisms. Until now, however, no PCS gene from liverworts, the earliest branch of land plants and possibly the first one to acquire a PCS with a C-terminal domain, has been characterized. In this study, we isolated and functionally characterized the first PCS gene from a liverwort, Marchantia polymorpha (MpPCS). MpPCS is constitutively expressed in all organs examined, with stronger expression in thallus midrib. The gene expression is repressed by Cd2+ and Zn2+. The ability of MpPCS to increase heavy metal resistance in yeast and to complement cad1-3 (the null mutant of the Arabidopsis ortholog AtPCS1) proves its function as the only PCS from M. polymorpha. Site-directed mutagenesis of the most conserved cysteines of the C-terminus of the enzyme further uncovered that two twin-cysteine motifs repress, to different extents, enzyme activation by heavy metal exposure. These results highlight an ancestral function of the PCS elusive C-terminus as a regulatory domain inhibiting enzyme overactivation by essential and non-essential heavy metals. The latter finding may be relevant for obtaining crops with decreased root to shoot mobility of cadmium, thus preventing its accumulation in the food chain.

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This paper reports functional studies on the enzyme phytochelatin synthase in the liverwort Marchantia polymorpha and the cyanobacterium Geitlerinema sp. strain PCC 7407. In vitro activity assays in control samples (cadmium-untreated) showed that phytochelatin synthase was constitutively expressed in both organisms. In the presence of 100 µM cadmium, in both the liverwort and the cyanobacterium, the enzyme was promptly activated in vitro, and produced phytochelatins up to the oligomer PC4. Likewise, in vivo exposure to 10–36 µM cadmium for 6-120 h induced in both organisms phytochelatin synthesis up to PC4. Furthermore, the glutathione (GSH) levels in M. polymorpha were constitutively low (compared with the average content in higher plants), but increased considerably under cadmium stress. Conversely, the GSH levels in Geitlerinema sp. PCC 7407 were constitutively high, but were halved under metal treatments. At odds with former papers, our results demonstrate that, as in M. polymorpha and other plants, the cyanobacterial phytochelatin synthase exposed to cadmium possesses manifest transpeptidasic activity, being able to synthesize phytochelatins with a degree of oligomerization higher than PC2. Therefore, prokaryotic and eukaryotic phytochelatin synthases differ less in functional terms than previously thought.

Forest management practices may heavily impact epiphytic (tree inhabiting) organisms. Retaining tree patches and buffer strips in logged stands may contribute to preserve ecosystem functioning and the vitality of epiphytic organisms in managed forests. To test these statements, the threatened forest macrolichen Lobaria pulmonaria (L.) Hoffm. was used as a model species, since it is a "flag" indicator species of forest ecosystems with long ecological continuity. To this purpose, photosynthetic performances, thallus anatomy and water holding capacity (WHC) of samples of L. pulmonaria were investigated in a logged mixed oak forest (Tuscany, Italy), confronting lichen thalli from retained-forest patches and retained-isolated trees, 18 months after logging. Compared with those of retained-forest patches, thalli on the trunks of retained-isolated trees were thinner and showed lower vitality (as indicated by the potential quantum yield of primary photochemistry-FV/FM and the index of overall photosynthetic performance-PIABS), as well as lower water holding capacity. In contrast, thalli from forest patches had performances comparable to those of healthy samples from unlogged forests.