Differential Metal Tolerance and Accumulation Patterns of Cd, Cu, Pb and Zn in the Liverwort Marchantia polymorpha L

Unveiling the molecular mechanisms of arsenic tolerance and resilience in the primitive bryophyte Marchantia polymorpha L

This study addresses the pressing issue of high arsenic (As) contaminations, which poses a severe threat to various life forms in our ecosystem. Despite this prevailing concern, all organisms have developed some techniques to mitigate the toxic effects of As. Certain plants, such as bryophytes, the earliest land plants, exhibit remarkable tolerance to wide range of harsh environmental conditions, due to their inherent competence. In this study, bryophytes collected from West Bengal, India, across varying contamination levels were investigated for their As tolerance capabilities. Assessment of As accumulation potential and antioxidant defense efficiency, including SOD, CAT, APX, GPX etc. revealed Marchantia polymorpha as the most tolerant species. It exhibited highest As accumulation, antioxidative proficiency, and minimal damage. Transcriptomic analysis of M. polymorpha exposed to 40 μM As(III) for 24 and 48 h identified several early responsive differentially expressing genes (DEGs) associated with As tolerance. These includes GSTs, GRXs, Hsp20s, SULTR1;2, ABCC2 etc., indicating a mechanism involving vacuolar sequestration. Interestingly, one As(III) efflux-transporter ACR3, an extrusion pump, known to combat As toxicity was found to be differentially expressed compared to control. The SEM-EDX analysis, further elucidated the operation of As extrusion mechanism, which contributes added As resilience in M. polymorpha. Yeast complementation assay using Δacr3 yeast cells, showed increased tolerance towards As(III), compared to the mutant cells, indicating As tolerant phenotype. Overall, these findings significantly enhance our understanding of As tolerance mechanisms in bryophytes. This can pave the way for the development of genetically engineered plants with heightened As tolerance and the creation of improved plant varieties.

Photosynthetic Efficiency of Marchantia polymorpha L. in Response to Copper, Iron, and Zinc

Metal micronutrients are essential for plant nutrition, but their toxicity threshold is low. In-depth studies on the response of light-dependent reactions of photosynthesis to metal micronutrients are needed, and the analysis of chlorophyll a fluorescence transients is a suitable technique. The liverwort Marchantia polymorpha L., a model organism also used in biomonitoring, allowed us to accurately study the effects of metal micronutrients in vivo, particularly the early responses. Gametophytes were treated with copper (Cu), iron (Fe) or zinc (Zn) for up to 120 h. Copper showed the strongest effects, negatively affecting almost the entire light phase of photosynthesis. Iron was detrimental to the flux of energy around photosystem II (PSII), while the acceptor side of PSI was unaltered. The impact of Fe was milder than that of Cu and in both cases the structures of the photosynthetic apparatus that resisted the treatments were still able to operate efficiently. The susceptibility of M. polymorpha to Zn was low: although the metal affected a large part of the electron transport chain, its effects were modest and short-lived. Our results may provide a contribution towards achieving a more comprehensive understanding of response mechanisms to metals and their evolution in plants, and may be useful for supporting the development of biomonitoring techniques.

Metal Detoxification in Land Plants: From Bryophytes to Vascular Plants. STATE of the Art and Opportunities

Potentially toxic elements are a widespread concern due to their increasing diffusion into the environment. To counteract this problem, the relationship between plants and metal(loid)s has been investigated in the last 30 years. In this field, research has mainly dealt with angiosperms, whereas plant clades that are lower in the evolutive scale have been somewhat overlooked. However, recent studies have revealed the potential of bryophytes, pteridophytes and gymnosperms in environmental sciences, either as suitable indicators of habitat health and elemental pollution or as efficient tools for the reclamation of degraded soils and waters. In this review, we summarize recent research on the interaction between plants and potentially toxic elements, considering all land plant clades. The focus is on plant applicability in the identification and restoration of polluted environments, as well as on the characterization of molecular mechanisms with a potential outlet in the engineering of element tolerance and accumulation.

Responses to Cadmium in Early-Diverging Streptophytes (Charophytes and Bryophytes): Current Views and Potential Applications

Several transition metals are essential for plant growth and development, as they are involved in various fundamental metabolic functions. By contrast, cadmium (Cd) is a metal that can prove extremely toxic for plants and other organisms in a dose-dependent manner. Charophytes and bryophytes are early-diverging streptophytes widely employed for biomonitoring purposes, as they are able to cope with high concentrations of toxic metal(loid)s without showing any apparent heavy damage. In this review, we will deal with different mechanisms that charophytes and bryophytes have evolved to respond to Cd at a cellular level. Particular attention will be addressed to strategies involving Cd vacuolar sequestration and cell wall immobilization, focusing on specific mechanisms that help achieve detoxification. Understanding the effects of metal(loid) pollution and accumulation on the morpho-physiological traits of charophytes and bryophytes can be in fact fundamental for optimizing their use as phytomonitors and/or phytoremediators.

Nickel excess affects phenology and reproductive attributes of Asterella wallichiana and Plagiochasma appendiculatum growing in natural habitats

Bryophytes are potent metal absorbers, thriving well on heavy metal (HM)-polluted soils. Mechanisms controlling uptake, compartmentalization and impacts of HMs on bryophytes life cycle are largely unknown. The current study is an effort to decipher mechanisms of nickel (Ni) excess-induced effects on the phenological events of two bryophytes, Asterella wallichiana and Plagiochasma apendiculatum growing in natural habitats. Observations revealed Ni-excess induced negative impacts on abundance, frequency of occurrence of reproductive organs, population viability and morphological traits, spore viability and physiological attributes of both the liverworts. Results led us conclude that P. appendiculatum survived better with the lowest impact on its life cycle events than A. wallichiana under Ni excess in natural habitats. Our findings collectively provide insights into the previously unknown mechanisms of Ni-induced responses in liverworts with respect to phenological attributes, as well as demonstrate the potential of P. appendiculatum to survive better in Ni excess habitats.

Eukaryotic and Prokaryotic Phytochelatin Synthases Differ Less in Functional Terms Than Previously Thought: A Comparative Analysis of Marchantia polymorpha and Geitlerinema sp. PCC 7407

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.

Bryophyte Communities along a Tropical Urban River Respond to Heavy Metal and Arsenic Pollution

Aquatic and rheophilous bryophytes can indicate water pollution as they bioaccumulate toxic water elements. We evaluated (1) bioaccumulation of eight heavy metals and arsenic by Marchantia polymorpha L., and (2) changes in bryophyte community structure, as responses to urban pollution in southern Ecuador. To this end, we registered presence/absence and coverage of submerged bryophytes in 120 quadrats across three zones of the Zamora river inside Loja city, and a control zone in a nearby forest. We found that the concentrations of five (Al, Cd, Cu, Fe, and Zn) of the eight chemical elements and arsenic were highest in urban M. polymorpha. Moreover, bryophyte species richness decreased in urban zones. Bryophyte community structure also differed between control and city zones, but no differences were found among city zones. The control zone was composed by a more distinct set of bryophyte species, e.g., an indicator species analysis showed that 16 species had high and significant indicator values for control zone, but only 11 species were indicators of at least one of the three urban zones. We concluded that bryophytes, in general, and M. polymorpha, in particular, can be suitable biomonitors of water quality in tropical urban rivers.

Lichens and Bromeliads as Bioindicators of Heavy Metal Deposition in Ecuador

We evaluated heavy metal deposition in Parmotrema arnoldii and Tillandsia usneoides in response to air pollution in Loja city, Ecuador. We assessed heavy metal (cadmium, copper, manganese, lead and zinc) content in these organisms at nine study sites inside Loja city and three control sites in nearby forests. Concentrations of all studied heavy metals (i.e., cadmium (Cd), copper (Cu), lead (Pb), manganese (Mn) and zinc (Zn)) were highest in downtown Loja. Our study confirms that passive monitoring using lichens and/or bromeliads can be an efficient tool to evaluate heavy metal deposition related to urbanization (e.g., vehicle emissions). We recommend these organisms to be used in cost-effective monitoring of air pollution in tropical countries.