Patterns of morphological, genetic and epigenetic variation (DNA methylation pattern) were investigated in metallicolous (M) and non-metallicolous (NM) populations of Armeria maritima. A morphological study was carried out using plants from six natural populations grown in a greenhouse. Morphological variation was assessed using seven traits. On the basis of this study, three representative populations were selected for molecular analyses using metAFLP to study sequence- and methylation-based DNA variation. Only one morphological trait (length of outer involucral bracts) was common to both metallicolous populations studied; however, the level of variation was sufficient to differentiate between M and NM populations. Molecular analyses showed the existence of naturally occurring epigenetic variation in A. maritima populations, as well as structuring into distinct between and within population components. We show that patterns of population genetic structure differed depending on the information used in the study. Analysis of sequence-based information data demonstrates the presence of three well-defined and genetically differentiated populations. Methylation-based data show that two major groups of individuals are present, corresponding to the division into M and NM populations. These results were confirmed using different analytical approaches, which suggest that the DNA methylation pattern is similar in both M populations. We hypothesise that epigenetic processes may be involved in microevolution leading to development of M populations in A. maritima.

BackgroundHeavy metal exposure affect plant productivity by interfering, directly and indirectly, with photosynthetic reactions. The toxic effect of heavy metals on photosynthetic reactions has been reported in wide-ranging studies, however there is paucity of data in the literature concerning thallium (Tl) toxicity. Thallium is ubiquitous natural trace element and is considered the most toxic of heavy metals; however, some plant species, such as white mustard (Sinapis alba L.) are able to accumulate thallium at very high concentrations. In this study we identified the main sites of the photosynthetic process inhibited either directly or indirectly by thallium, and elucidated possible detoxification mechanisms in S. alba.ResultsWe studied the toxicity of thallium in white mustard (S. alba) growing plants and demonstrated that tolerance of plants to thallium (the root test) decreased with the increasing Tl(I) ions concentration in culture media. The root growth of plants exposed to Tl at 100 μg L−1 for 4 weeks was similar to that in control plants, while in plants grown with Tl at 1,000 μg L−1 root growth was strongly inhibited. In leaves, toxic effect became gradually visible in response to increasing concentration of Tl (100 − 1,000 μg L−1) with discoloration spreading around main vascular bundles of the leaf blade; whereas leaf margins remained green. Subsequent structural analyses using chlorophyll fluorescence, microscopy, and pigment and protein analysis have revealed different effects of varying Tl concentrations on leaf tissue. At lower concentration partial rearrangement of the photosynthetic complexes was observed without significant changes in the chloroplast structure and the pigment and protein levels. At higher concentrations, the decrease of PSI and PSII quantum yields and massive oxidation of pigments was observed in discolored leaf areas, which contained high amount of Tl. Substantial decline of the photosystem core proteins and disorder of the photosynthetic complexes were responsible for disappearance of the chloroplast grana.ConclusionsBased on the presented results we postulate two phases of thallium toxicity on photosynthesis: the non-destructive phase at early stages of toxicant accumulation and the destructive phase that is restricted to the discolored leaf areas containing high toxicant content. There was no distinct border between the two phases of thallium toxicity in leaves and the degree of toxicity was proportional to the migration rate of the toxicant outside the vascular bundles. The three-fold (nearly linear) increase of Tl(I) concentration was observed in damaged tissue and the damage appears to be associated with the presence of the oxidized form of thallium − Tl(III).Electronic supplementary materialThe online version of this article (doi:10.1186/s12870-016-0883-4) contains supplementary material, which is available to authorized users.

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Cryopreservation is widely applied to many economically important species excluding chimera plants which are problematic for long-term conservation. Their storage problems can be circumvented only by cryopreserving meristems. This study looked at the morphogenetic response of shoot tips of periclinal chimera chrysanthemum 'Lady Orange' and 'Lady Salmon', as well as the solid mutant 'Richmond', that were cryopreserved by encapsulation-dehydration technique. By applying 10 µM ABA in the preculture medium followed by 4-day-long dehydration treatment, the explant survival reached up to 67%. Besides the stimulation of typical single shoot recovery, cryopreservation led to direct or indirect multiple shoot formation, shoot malformation, as well as inhibited their spontaneous rooting. Microscopic analysis revealed three types of structural damages of shoot tips which can correspond with their morphogenetic response in recovery culture. No influence of cryostorage on the acclimatisation efficiency of the recovered chrysanthemums was observed.

Biscutella laevigata L. is known as a Tl hyperaccumulator. In Poland Biscutella laevigata occurs in the Tatra Mts (Western Carpathians) and on the calamine waste heap in Bolesław near Olkusz (Silesian Upland). The purpose of this work was to evaluate whether plants of both populations were able to accumulate an elevated amount of thallium in their tissues. The plants were cultivated in calamine soil in a glasshouse for a season and studied at different ages -from 2-week-old seedlings to 10-month-old adults. Additionally, the plants were grown for ten weeks in calamine soil with EDTA to enhance Tl bioavailability. The total content of Tl in plant tissues after digestion was determined by ICP-MS, whereas its distribution in leaves was studied by LA-ICP-MS. Of the total content of Tl in the soil in the range of (15. . The translocation factor was 6.1 in the soil and 2.2 in the soil with EDTA; the bioconcentration factor amounted to 10.9 and 5.8, respectively. The plants from both populations did not contain a Tl amount clearly indicating hyperaccumulation (100-500 mg•kg -1 d.m.), however, high (>1) translocation and bioconcentration factors suggest such an ability. It is a characteristic species-wide trait; B. laevigata L. is a facultative Tl hyperaccumulator. The largest Tl amount was located at the leaf base, the smallest at its top. Thallium also occurred in trichomes, which was presented for the first time; in this way plants detoxify Tl in the above-ground parts. Leaves were much more hairy in the Bolesław plants. This is an adaptation for growth in the extreme conditions of the zinc-lead waste heap with elevated Tl quantity.