Effect of copper stress on cup lichens Cladonia humilis and C. subconistea growing on copper-hyperaccumulating moss Scopelophila cataractae at copper-polluted sites in Japan

Heavy Metal Accumulation and Copper Localization in Scopelophila cataractae in Thailand

Four specimens of gametophores and protonemata of Scopelophila cataractae (copper moss) were collected from a stream in Doi Suthep-Pui National Park, Thailand in order to determine heavy metal accumulation and Cu localization. The order of total metal concentrations in the protonemata and leaf cell surfaces of S. cataractae was Fe > Zn > Cu. Significant Cu values (> 400 mg kg^-1) were found in both gametophores and protonemata. Growth substrates were considered as a key source of heavy metals in the sampling stream. X-ray spectrometry (EDS micro-analyser) detected the localization of ten elements (C, O, Mg, Al, Si, Ca, S, Cu, Zn and In); substantial atomic percentages of Al, Cu and Zn were noted in leaf surfaces and protonemata. These metallic elements were found in highest proportion. To some extent, cell surfaces at the basal leaf costa showed the highest peak value compared to medial and apical leaf portions (≈ 4.3 at.%). This Cu moss can be used as a bioindicator to reflect anthropogenic activities in stream ecosystems.

Effect of Cu on the fluorescence of the Cu-hyperaccumulator lichen Stereocaulon sorediiferum

Stereocaulon sorediiferum is expected to be a Cu-hyperaccumulator lichen and has fluorescent substances. To clarify the relationship between the fluorescence (FL) of the lichen and its Cu concentration, we collected S. sorediiferum samples at Cu-contaminated and uncontaminated sites in Japan, determined the concentration of Cu, K, Mg, Al, Ca, Mn, Fe, Zn, chlorophyll a,b, and total carotenoids in them, analyzed lichen secondary metabolites and fluorescent substances extracted from them, and measured the FL of them and their extracts. We found that the FL intensity of S. sorediiferum samples is significantly negatively correlated with their Cu concentration. The application of its FL for Cu monitoring may allow a new nondestructive quantitative method for assessing Cu contamination. The spectroscopic and chromatographic analysis shows that the fluorescent substances negatively correlated with Cu concentration are not major lichen secondary metabolites (lobaric acid and atranorin) and remain after immersion in acetone. The correlation analysis and the comparison with the causal relationship between Cu concentration and the chlorophyll a/b ratio suggest that the reason for the decrease in FL intensity with increasing Cu concentration is a structural change of the fluorescent substances by accumulated Cu. These findings lead to a better understanding of the relationship between the FL of S. sorediiferum and its Cu concentration and provide new insights into fluorescent lichen substances.

Heavy-metal tolerance of photobiont in pioneer lichens inhabiting heavily polluted sites

Heavy metals are known for their negative impact on the physiological processes of lichen photobiont. In spite of this, certain lichens are known to be effective pioneers of polluted sites. Cladonia cariosa, C. rei, and Diploschistes muscorum are prominent examples of lichens that spontaneously colonise post-industrial wastes. We examined the effect of total and intracellular Zn, Pb, Cd, As, Cu, and Ni accumulation in the thalli of these species on the physiological parameters of photobiont. Increased accumulation of Zn, Cd, Cu, and Ni in D. muscorum and of Zn and Ni in C. rei negatively affected contents of photosynthetic pigments, whereas concentrations of Pb had a positive effect in all lichen species. Moreover, pigment contents were positively associated with the concentrations of most examined elements in C. cariosa. The results indicate that even if chlorophyll contents reduced, its degradation does not progress. This suggests that metal stress may exert a negative effect on the synthesis rather than on the integrity of chlorophyll. Most importantly, lichen samples of each of the species from polluted sites proved to possess significantly higher F_V/F_M ratios than those from a reference site; moreover, the contents of elements of lichen thalli positively influenced this parameter. The efficient functioning of the algal component under heavy-metal stress conditions indicates that the examined lichens are well adapted to extremely contaminated substrates.

Response of secondary metabolites to Cu in the Cu-hyperaccumulator lichen Stereocaulon japonicum

Lichen secondary metabolites are known to be associated with heavy metal uptake and tolerance in lichens. Understanding the relationship between their secondary metabolites and heavy metals in them is important for clarifying the mechanisms of their heavy metal accumulation and tolerance. To determine the relationships between the concentrations of secondary metabolites and Cu in the Cu-hyperaccumulator lichen Stereocaulon japonicum and to clarify its response to Cu, we collected Cu-contaminated and uncontaminated samples of the lichen and determined relative concentrations of secondary metabolites and concentrations of Cu, K, glucose, and sugar alcohols in them. We found significant negative correlations between the relative concentrations of secondary metabolites-atranorin and stictic acid-and the concentration of Cu. These negative correlations can be interpreted in one of two ways: (a) S. japonicum itself reduced the relative concentrations of secondary metabolites in response to the increase of Cu concentration or (b) its carbon and energy metabolism was damaged by Cu stress, resulting in the reduction of the relative concentrations of secondary metabolites. The analysis of K, glucose, and sugar alcohols showed no effect of Cu on these concentrations, which means that the carbon and energy metabolism was not damaged by Cu stress. Therefore, the negative correlations can be interpreted that S. japonicum itself reduced the relative concentrations of secondary metabolites with the increase of Cu concentration. These findings provide a deeper understanding of the response of secondary metabolites to Cu in the lichen.

Effects of Cu on the content of chlorophylls and secondary metabolites in the Cu-hyperaccumulator lichen Stereocaulon japonicum

Understanding the relationship between Cu and Cu-hyperaccumulator lichens is important for their application in monitoring and assessing heavy metal pollution. We investigated the Cu-hyperaccumulator lichen Stereocaulon japonicum at several Cu-polluted and control sites in Japan, and found the lichen to be widely distributed. Its concentrations of Cu, chlorophylls, and secondary metabolites, chlorophyll-related indices, and absorption spectra were measured, and we observed negative effects of Cu on these concentrations and indices. For highly Cu-polluted samples (>100ppm dry weight), however, we found significant linear correlations between Cu and chlorophyll concentrations. This can be considered as the response of the photobiont in S. japonicum to Cu stress. In highly Cu-polluted samples the chlorophyll-related indices and concentration of total secondary metabolites were almost constant regardless of Cu concentration. This suggests that the increase in chlorophyll concentration with the increase in Cu concentration enhances photosynthetic productivity per unit biomass, which will allow the production of extra structure and energy for maintaining the chlorophyll-related indices under Cu stress. The relationship between the increase in chlorophyll concentration of S. japonicum and the decrease in secondary metabolite concentration of the lichen can be explained by considering the balance of carbohydrates in the lichen. We found that a spectral index A372-A394 can be a useful index of the concentrations of Cu and total secondary metabolites in S. japonicum. These findings show the adjustment of the content of chlorophylls and secondary metabolites in S. japonicum to Cu stress, and provide a better understanding of the relationship between Cu and the Cu-hyperaccumulator lichen.

Effect of metal stress on photosynthetic pigments in the Cu-hyperaccumulating lichens Cladonia humilis and Stereocaulon japonicum growing in Cu-polluted sites in Japan

To understand the ecology and physiology of metal-accumulating lichens growing in Cu-polluted sites, we investigated lichens near temple and shrine buildings with Cu roofs in Japan and found that Stereocaulon japonicum Th. Fr. and Cladonia humilis (With.) J. R. Laundon grow in Cu-polluted sites. Metal concentrations in the lichen samples collected at some of these sites were determined by inductively coupled plasma mass spectroscopy (ICP-MS). UV-vis absorption spectra of pigments extracted from the lichen samples were measured, and the pigment concentrations were estimated from the spectral data using equations from the literature. Secondary metabolites extracted from the lichen samples were analyzed by high-performance liquid chromatography (HPLC) with a photodiode array detector. We found that S. japonicum and C. humilis are Cu-hyperaccumulating lichens. Differences in pigment concentrations and their absorption spectra were observed between the Cu-polluted and control samples of the 2 lichens. However, no correlation was found between Cu and pigment concentrations. We observed a positive correlation between Al and Fe concentrations and unexpectedly found high negative correlations between Al and pigment concentrations. This suggests that Al stress reduces pigment concentrations. The concentrations of secondary metabolites in C. humilis growing in the Cu-polluted sites agreed with those in C. humilis growing in the control sites. This indicates that the metabolite concentrations are independent of Cu stress.