Impacts of Cd Pollution on the Vitality, Anatomy and Physiology of Two Morphologically Different Lichen Species of the Genera Parmotrema and Usnea, Evaluated under Experimental Conditions

Abstract

The heavy metal Cd accumulates in trophic chains, constituting a toxic element for photosynthesizing organisms, including the algal photobionts of lichen. Thus, as lichens respond differently to heavy metal toxicity, we hypothesized that the species Parmotrema tinctorum and Usnea barbata, commonly sampled in the Cerrado ecoregion, could be sensitive to Cd and, therefore, be used to biomonitor the dispersion of this metal. We also aimed to indicate the responsiveness of biological markers to Cd in these species by exposing the thalli to simulated rainfall with increasing metal concentrations. We observed that both lichen species are responsive to Cd stress; however, different pathways are accessed. The synthesis of carotenoids by P. tinctorum and the production of antioxidant enzymes by U. barbata seem to constitute relevant response strategies to Cd-induced stress. The lichen morphoanatomy, cell viability, photobiont vitality index, chlorophyll a fluorescence, and chlorophyll a synthesis were efficient biomarkers for the effects of increasing Cd exposure in P. tinctorum, being the variables primarily associated with damage to the photobiont. For U. barbata, the lichen morphoanatomy, photochemistry, and antioxidant enzyme activity (catalase, superoxide dismutase and ascorbate peroxidase) were essential to reflect Cd toxicity. However, the species P. tinctorum was characterized as the most sensitive to Cd toxicity, constituting a good bioindicator for the presence of this metal. It can be used in the diagnosis of air quality in urban and industrial areas or even in forest areas influenced by Cd in phosphate fertilizers.

Mercury Content and Amelioration of Its Toxicity by Nitric Oxide in Lichens

“…The same ROS stimulation has been observed in the green alga exposed to 100 µM Hg, but not Pb [ 14 ], or in plant roots exposed to Hg [ 30 ], providing evidence that Hg is more toxic than many other common metallic contaminants. It is also known that oxidative stress markers differ in lichens treated by metals in relation to morphology and even depleted H 2 O 2 content was observed after spray application of Cd [ 31 ], while immersion in Cd-enriched solutions led to enhanced ROS or H 2 O 2 formation detected by fluorescence microscopy and standard spectrophotometry [ 18 ].…”

Lichen Biodiversity and Near-Infrared Metabolomic Fingerprint as Diagnostic and Prognostic Complementary Tools for Biomonitoring: A Case Study in the Eastern Iberian Peninsula

“…This approach builds on the assumption that air pollutants can cause physical and physiological alterations to lichens, resulting in visible injuries on their thalli (e.g., damage or discoloration) [25]. For example, in the case of Parmotrema tinctorum and Usnea barbata, the lichen morphoanatomy and photochemistry have been demonstrated to be efficient biomarkers for the effects of exposure to increasing concentrations of Cd [31].…”

“…Biomonitoring methods based on the diversity of epiphytic lichens are among the most used worldwide [15]. In addition, evidence of pollutant impacts can be observed as symptoms of damage in lichen thalli, involving morphological and physiological alterations and fluctuations in lichen growth [29][30][31]. In this way, lichens can provide information related to pollutant concentrations in the monitored area [23,32,33].…”

Application of a Fluorescence-Based Instrument Prototype for Chlorophyll Measurements and Its Utility in an Herbicide Algal Ecotoxicity Assay

“…The parameter Rfd is usually used for biotic and abiotic plant stress detection [82,83], and it is considered to be a good and rapid indicator of the vitality of plants. In many cases, it has already proved to be a very sensitive indicator of metabolic disturbances caused by different types of stress (e.g., salinity [84], nutrient enrichment [85], heavy metals [86]). It is reported to disturb the photochemical reactions in photosystem II, resulting in less efficient photosynthesis [85,86].…”

“…In many cases, it has already proved to be a very sensitive indicator of metabolic disturbances caused by different types of stress (e.g., salinity [84], nutrient enrichment [85], heavy metals [86]). It is reported to disturb the photochemical reactions in photosystem II, resulting in less efficient photosynthesis [85,86]. In the present study, this parameter was also presented as the most sensitive biomarker for the investigation of the effects of an herbicide.…”