Recent developments in knowledge about the interactions between lichens and heavy metals at different levels, from populations to cells and from ecology to molecular biology are reviewed. Sources of heavy metals, mechanisms of heavy metal accumulation and detoxification by lichens are discussed. Special emphasis is placed on ultrastructural changes as well as physiological parameters such as membrane integrity, pigment composition, chlorophyll a fluorescence, photosynthesis, respiration, contents of ATP, amino acids, ergosterol, ethylene, non-protein thiols, activity of antioxidant enzymes and expression of stress proteins.

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Cadmium and copper uptake and its consequence for activity of selected enzymes of phenolic metabolism, phenolic acids accumulation, quantity of mineral nutrients and stress-related parameters in Matricaria chamomilla plants exposed to 60 μM and 120 μM for 7 days has been studied. Cu content in the above-ground biomass was ca. 10-fold lower compared to Cd and amount of Cd in the methanol-soluble fraction was lower than in the water-soluble fraction. "Intra-root" Cd represented 68% and 63% of total Cd content at 60 μM and 120 μM, but no difference was observed in Cu-exposed roots. Cu excess had more pronounced effect on shikimate dehydrogenase, cinnamyl alcohol dehydrogenase, polyphenol oxidase and ascorbate peroxidase activity mainly in the roots. Among eight detected benzoic acid derivatives and four cinnamic acid derivatives, the latter were preferentially accumulated in response to Cd excess. Content of salicylic acid increased in all variants. Amount of superoxide was elevated in both the rosettes (preferentially by Cu) and roots (preferentially by Cd). Accumulation of Ca and Mg was not affected by excess of metals, while potassium decreased in both the rosettes and roots (Cu caused stronger depletion). Amount of Fe increased in the roots in response to both metals (more expressively in Cu-treated ones). Present study using other metabolic parameters (and supplementing our previous studies) has confirmed higher Cu toxicity for chamomile plants, to support its strong pro-oxidant properties. These observations as complex metabolic responses are discussed.

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Host use and selection by herbivores are often determined by host chemistry. Lichen secondary chemicals frequently have been assumed to have a defensive role against herbivores similar to that of higher plants, but thus far there is only circumstantial evidence of the adverse effect of lichen secondary chemicals on specialized lichen‐feeders. We studied the impact of lichen secondary metabolites on performance and host preference of lichenivorous larvae of the moth Eilema depressum using a recently developed manipulation method that allows the removal of a major part of lichen secondary metabolites from the extracellular space of the lichen thallus without harming their primary metabolism. All larvae died on intact thalli of Vulpicida pinastri and Hypogymnia physodes, whereas, after extraction of most of the lichens' secondary chemicals (e.g., pinastric and physodic acids, respectively), survival of neonate larvae ranged between 75% and 85%. In turn, atranorin, the major secondary metabolite in the cortical layer of Parmelia sulcata, merely retarded the growth of larvae during their first days, but had no long‐term impact on survival or performance of larvae. In preference experiments, treated thalli with lowered concentrations of lichen secondary metabolites, with the exception of Xanthoria parietina, were preferred to intact thalli containing secondary chemicals. Our results show that lichen secondary metabolites may act, at natural concentrations, as strong antiherbivore compounds against E. depressum larvae and may play an important role in their host selection.

The influence of salicylic acid (SA) doses of 50 and 250 microM, for a period of up to 7 days, on selected physiological aspects and the phenolic metabolism of Matricaria chamomilla plants was studied. SA exhibited both growth-promoting (50 microM) and growth-inhibiting (250 microM) properties, the latter being correlated with decrease of chlorophylls, water content and soluble proteins. In terms of phenolic metabolism, it seems that the higher SA dose has a toxic effect, based on the sharp increase in phenylalanine ammonia-lyase (PAL) activity (24 h after application), which is followed by an increase in total soluble phenolics, lignin accumulation and the majority of the 11 detected phenolic acids. Guaiacol-peroxidase activity was elevated throughout the experiment in 250 microM SA-treated plants. In turn, some responses can be explained by mechanisms associated with oxidative stress tolerance; these mitigate acute SA stress (which is indicated by an increase in malondialdehyde content). However, PAL activity decreased with prolonged exposure to SA, indicating its inhibition. Accumulation of coumarin-related compounds (umbelliferone and herniarin) was not affected by SA treatments, while (Z)- and (E)-2-beta-D: -glucopyranosyloxy-4-methoxycinnamic acids increased in the 250 microM SA-treated rosettes. Free SA content in the rosettes increased significantly only in the 250 microM SA treatment, with levels tending to decrease towards the end of the experiment and the opposite trend was observed in the roots.

Phenylalanine ammonia-lyase activity (PAL, EC 4.3.1.5), total phenolics, soluble proteins, malondialdehyde and metals accumulation in four-week old chamomile (Matricaria chamomilla) plants cultivated in nutrient solution and exposed to low (3 μM) and high (60 and 120 μM) levels of cadmium (Cd) or copper (Cu) for 7 days were studied. High Cd concentrations had a stimulatory effect on PAL activity and soluble phenolics accumulation while high Cu doses decreased soluble proteins in the leaf rosettes. In the roots, extreme stimulatory effects of 60 and 120 μM Cu were observed on PAL activity, phenolics and malondialdehyde accumulation, while protein content was reduced by these Cu doses. Cd accumulation was higher in the leaf rosettes compared to copper, but the opposite was recorded in the roots. Taken together, the stimulatory effect of Cu on phenolic metabolism was recorded, even though high malondialdehyde accumulation may be an indication that phenolics was not sufficient to counteract reactive oxygen species formation thus leading to damage of membrane integrity. In comparison to Cd, Cu had more noticeable effect on the parameters studied to support its strong redox-active properties. These facts in correlation to antioxidative properties of phenolic metabolites are also discussed.