Multiple mechanisms of heavy metal tolerance are differentially expressed in ecotypes of Artemisia fragrans

•Morphological differences of Artemisia fragrans ecotypes is revealed during generative stage.•A. fragrans ecotypes accumulated Cd in a range of its toxicity level for most plants.•Ecotype-specific mechanism in internal distribution of metals within leaf tissues was revealed.•Cd exclusion from photosynthetically active tissues is considered as major tolerance mechanism.

Artemisia fragrans is a plant species with ability of growing on heavy metal-polluted soils. Ecotypes of this species naturally growing in polluted areas can accumulate and tolerate different amounts of heavy metals (HM), depending on soil contamination level at their origin. Heavy metal tolerance of various ecotypes collected from contaminated (AP, SP) and non-contaminated (BG) sites was compared by cultivation on a highly HM-contaminated river sediment and a non-contaminated agricultural control soil.Tissue-specific HM distribution was analyzed by laser ablation-inductively-coupled plasma-mass spectroscopy (LA-ICP-MS) and photosynthetic activity by non-invasive monitoring of chlorophyll fluorescence.Plant-mineral analysis did not reveal ecotype-differences in concentrations of Cd, Zn, Cu in shoots of Artemisia plants, suggesting no differential expression of root uptake or root to shoot translocation of HM. There was also no detectable rhizosphere effect on HM concentrations on the contaminated soil. However, despite high soil contaminations, all ecotypes accumulated Zn only in the concentration range of generally reported for normal growth of plants, while Cu and Cd concentrations were close to or even higher than the toxicity level for most plants. As a visible symptom of differences in HM tolerance, only the AP ecotype was able to enter the generative phase to complete its life cycle. Analysis of tissue-specific metal distribution revealed significantly lower concentrations of Cd in the leaf mesophyll of this ecotype, accumulating Cd mainly in the leaf petioles. A similar mesophyll exclusion was detectable also for Cu, although not associated with preferential accumulation in the leaf petioles. However, high mesophyll concentrations of Cd and Cu in the SP and BG ecotypes were associated with disturbances of the photosynthetic activity.The findings demonstrate differential expression of HM exclusion strategies in Artemisia ecotypes and suggest Cd and Cu exclusion from the photosynthetically active tissues as a major tolerance mechanism of the AP ecotype.

Graphical abstractCadmium compartmentation in the petioles of ecotype originating from an area around Aluminum Plant (AP ecotype) was revealed as a major Cd tolerance mechanism restricting it from the photosynthetically active tissues.LA-ICP-MS analysis of the spatial distribution of Cd in the cross sections petiole of Artemisia fragrans ecotypes grown for 80 days in the Kuchenbuch growth system (Engels et al., 2000) on non-contaminated control and heavy metal contaminated soils. The Cd concentrations in leaves of the AP ecotype are expressed as the 111Cd:13C ratio along the ablation pathway through the plant tissue.Download high-res image (259KB)Download full-size image