Morphological versus genetic diversity of Viola reichenbachiana and V. riviniana (sect. Viola, Violaceae) from soils differing in heavy metal content

Micro-Evolutionary Processes in Armeria maritima at Metalliferous Sites

Tolerance to heavy metals in plants is a model process used to study adaptations to extremely unfavorable environments. One species capable of colonizing areas with high contents of heavy metals is Armeria maritima (Mill.) Wild. A. maritima plants growing in metalliferous areas differ in their morphological features and tolerance levels to heavy metals compared to individuals of the same species growing in non-metalliferous areas. The A. maritima adaptations to heavy metals occur at the organismal, tissue, and cellular levels (e.g., the retention of metals in roots, enrichment of the oldest leaves with metals, accumulation of metals in trichomes, and excretion of metals by salt glands of leaf epidermis). This species also undergoes physiological and biochemical adaptations (e.g., the accumulation of metals in vacuoles of the root's tannic cells and secretion of such compounds as glutathione, organic acids, or HSP17). This work reviews the current knowledge on A. maritima adaptations to heavy metals occurring in zinc-lead waste heaps and the species' genetic variation from exposure to such habitats. A. maritima is an excellent example of microevolution processes in plants inhabiting anthropogenically changed areas.

Innate, High Tolerance to Zinc and Lead in Violets Confirmed at the Suspended Cell Level

Many species of the Viola L. genus (violets) colonize areas with high concentrations of trace elements in the soil, e.g., nickel, cadmium, zinc, and lead. Although tolerance to heavy metals is a common phenomenon in violets, it is not clear whether this is the result of gradual microevolutionary processes as a part of the adaptation to the specific conditions, or whether the tolerance was inherited from the ancestor(s). We developed cell suspension cultures of five plant species: two non-metallophytes—Arabidopsis thaliana (Col-0) and Viola · wittrockiana, and three metallophytes—V. philippica, V. tricolor, and Silene vulgaris subsp. humilis for tolerance tests. The aim of the study was to measure the level of tolerance of violets in comparison with species from the other genera to verify the hypothesis of the high, innate tolerance of the former. We measured cell viability, non-enzymatic antioxidant content, and the accumulation of heavy metals after cell treatment with Zn or Pb. The results indicate they are innate and independent on the ecological status (metallophyte vs. non-metallophyte) and high in comparison with other species tolerance to Zn and Pb in violets. Viability of the cells after Zn and Pb (1000 μM) exposure for 72 h was the highest in violets. Antioxidant content, after heavy metal treatment, increased significantly, particularly in metallophyte violets, indicating their high responsivity to metals. In all species, lead was detected in the protoplasm of the cells, not in the vacuole or cell wall. All violets were characterized by the accumulation capacity of lead. Here, we clearly show that the physiological and biochemical studies conducted with the use of heavy metals on plant cells translate into the heavy metal tolerance of the species.

Classical Morphometrics in V. arvensis and V. kitaibeliana (Viola sect. Melanium) Reveals Intraspecific Variation with Implications for Species Delimitation: Inferences from a Case Study in Central Italy

The high morphological variability of Viola arvensis may hinder the proper identification of the closely related species with an implication for biodiversity surveys. Variation in floral and vegetative morphology was explored in V. arvensis, compared to V. kitaibeliana, based upon 14 wild Italian populations, to provide new insights into their diagnostic features. Species were characterized using 32 morphological descriptors assessed on 272 flowers and as many leaves and scored as quantitative and categorical variables. Statistical methods, including Linear Discriminant Analysis (LDA), were applied to test species delimitation. Data highlighted variations in sepal size, petal size, leaves shape, stylar dark spot, and pollen magazine higher within V. arvensis than between V. arvensis and V. kitaibeliana. LDA partitioned the V. arvensis samples into two distinct clusters; no clear distinction was found between the cluster combining individuals from grasslands and V. kitaibeliana. The separation of V. arvensis and V. kitaibeliana from V. tricolor, included as a reference, was noticeable. Correlations were found in all species between the flower/leaf position on the stem and some floral and vegetative features. The shape and margin of the lower sepal, the stylar flap, and the lamina margin and apex were diagnostic in field identification. The results support the recognition of an undescribed V. arvensis eco-phenotype linked to seminatural dry grasslands, easily distinguishable from the field-grown type of V. arvensis but hardly distinguishable from the dwarf pansy. Data further corroborate the assumption of general deep-rooted confusion in ascribing poorly developed individuals of V. arvensis to the rare and locally threatened V. kitaibeliana, leading to potential implications for its conservation.

Seasonal and Simultaneous Cleistogamy in Rostrate Violets (Viola, subsect. Rostratae, Violaceae)

The special mixed reproductive system, i.e., the ability of an individual plant to develop both open, chasmogamous (CH) flowers adapted to cross-pollination and closed, cleistogamous (CL) flowers with obligate self-pollinating, is a common phenomenon in Viola L. In most sections of Northern Hemisphere violets, cleistogamy is seasonal, and CH and CL flowers develop sequentially in the season. Non-seasonal cleistogamy (simultaneous) is a rare phenomenon in rostrate violets. In the current study, we focused on modification of the CH/CL mating system in V. caspia by environmental conditions, resulting in a gradual switch from temporal cleistogamy, occurring in nature, to simultaneous cleistogamy under greenhouse conditions. V. reichenbachiana with seasonal cleistogamy was the control for V. caspia with the labile seasonal/simultaneous cleistogamy system. In simultaneous cleistogamy, the CH and CL flowers, fruits and seeds developed on an individual plant at the same time on the same branch. The typical difference between CH and CL flowers’ pistils is a straight style ending with a head-like stigma in CH and a curved style in CL adapted to self-pollination. This trait persists in the fruit and seed stages, allowing for easy recognition of fruit of CL and CH flowers in simultaneous cleistogamy. Floral meristems of CH flowers of V. reichenbachiana developed on the rhizome at the end of the growing season under short-day conditions and remained dormant until the following season. The CL floral meristems formed under long-day conditions on elongating lateral branches in the upper leaf axils. The daily temperature influenced the variable CH/CL ratio of V. caspia in nature and greenhouse conditions. Regulation of the CL/CH flower ratio by modifying environmental factors is important for basic research on genetic/epigenetic regulation of cleistogamy and for practical use to produce genetically stable lines of economically important species via CL seeds.

Phytostabilization potential of Erica australis L. and Nerium oleander L.: a comparative study in the Riotinto mining area (SW Spain)

Phytostabilization is a green, cost-effective technique for mine rehabilitation and ecological restoration. In this study, the phytostabilization capacity of Erica australis L. and Nerium oleander L. was assessed in the climatic and geochemical context of the Riotinto mining district, southwestern Spain, where both plant species colonize harsh substrates of mine wastes and contaminated river banks. In addition to tolerating extreme acidic conditions (up to pH 3.36 for E. australis), both species were found to grow on substrates very poor in bioavailable nutrients (e.g., N and P) and highly enriched with potentially phytotoxic elements (e.g., Cu, Cd, Pb, S). The selective root absorption of essential elements and the sequestration of potentially toxic elements in the root cortex are the main adaptations that allow the studied species to cope in very limiting edaphic environments. Being capable of a tight elemental homeostatic control and tolerating extreme acidic conditions, E. australis is the best candidate for use in phytostabilization programs, ideally to promote early stages of colonization, improve physical and chemical conditions of substrates and favor the establishing of less tolerant species, such as N. oleander.

From cells highly tolerant to Zn and Pb to fully fertile plants - Selection of tolerant lines with in vitro culture

Viola arvensis cells were selected after treatment with Zn or Pb and regenerated into plants likely to have higher tolerance levels than the initial plant. The surviving cells in the suspension treated with 2000 μM of Zn, 2000 μM of Pb or 0 μM for 72 h were maintained on a solidified half-strength MS medium supplemented with 0.5 mg L^-1 TDZ to induce divisions and organogenesis. The adventitious shoots obtained were rooted on a half-strength MS medium with 1 mg L^-1 IBA. Regenerants derived from the Zn- and Pb-treated cells were vigorous and fully fertile. The in vitro conditions and metal impact generated a low genome alteration and overall low genetic diversity of regenerants compared to the initial plant and plants from the natural population. The cells of regenerants obtained after Pb treatment represented an approximately 12% higher tolerance level to Pb than the cells of the initial plant. This is the first report of plant regeneration from highly tolerant cells selected by heavy metal treatment. Regenerants successfully obtained in vitro could be considered as a source material for the recultivation of areas polluted with heavy metals.

No evidence of contemporary interploidy gene flow between the closely related European woodland violets Viola reichenbachiana and V. riviniana (sect. Viola, Violaceae)

Viola reichenbachiana (2n = 4x = 20) and V. riviniana (2n = 8x = 40) are closely related species widely distributed in Europe, often sharing the same habitat throughout their overlapping ranges. It has been suggested in numerous studies that their high intraspecific morphological variability and plasticity might have been further increased by interspecific hybridisation in contact zones, given the sympatry of the species and the incomplete sterility of their hybrid. The aims of this study were to: (i) confirm that V. reichenbachiana and V. riviniana have one 4x genome in common, and (ii) determine the impact of hybridisation and introgression on genetic variation of these two species in selected European populations. For our study, we used 31 Viola populations from four European countries, which were analysed using AFLP and sequencing of a variable plastid intergenic spacer, trnH-psbA. Our analysis revealed that V. reichenbachiana exhibited larger haplotype diversity, having three species-specific haplotypes versus one in V. riviniana. The relationships among haplotypes suggest transfer of common haplotypes into V. riviniana from both V. reichenbachiana and hypothetically the other, now extinct, parental species. AFLP analysis showed low overall genetic diversity of both species, with V. riviniana showing higher among-population diversity. None of the morphologically designated hybrid populations had additive AFLP polymorphisms that would have indicated recent hybridisation. Also, kinship coefficients between both species did not indicate gene flow. V. riviniana showed significant population subdivision and significant isolation by distance, in contrast to V. reichenbachiana. The results indicate lack of gene flow between species, high influence of selfing on genetic variability, as well as probably only localised introgression toward V. riviniana.

Вплив екскрецій Capreolus capreolus і Sus scrofa на активність аланінамінотрансферази в листках Glechoma hederacea в умовах забруднення кадмієм

Досліджено активність (нМ піровиноградної кислоти/мл∙с) ферменту азотного метаболізму аланінамінотрансфераза (АLТ, EC 2.6.1.2) та вміст альбумінів (мг/мл) у листках Glechoma hederacea L., яка домінувала на дослідній території (липово-ясенева діброва зі Stellaria holostea L.) на фоні солей Cd, екскретів ссавців Capreolus capreolus L. та Sus scrofa L. та їх спільної дії. Cd вносили у вигляді солі Cd(NO3)2 у концентраціях 0,25, 1,25, та 2,50 г/м2, що еквівалентно 1, 5 та 10 ГДК Cd. При внесенні враховували кількість ГДК для Cd (5 мг/кг ґрунту). Виявлено достовірне інгібіювання активності АЛТ у 3–4 рази (на фоні 1 та 5 ГДК Cd). Подібний відгук на стрес відбувався й у білковому метаболізмі. Визначено достовірне зниження вмісту альбумінів до 72% та 80% (на фоні 1 та 5 ГДК Cd) відносно контролю (ділянка без забруднення Cd та екскретів ссавців), що доводить неспецифічність реакції на стрес. Використання екскрементів C. capreolus та S. scrofa показало нівелювання впливу Cd за рахунок підвищення активності метаболізму АЛТ на 41% та 105% відповідно (на фоні 1 ГДК Cd) відносно контролю (контроль 1 ГДК Cd). Дія Cd у дозі 5 ГДК достовірно відносно контролю (контроль 5 ГДК Cd) нівельована тільки на фоні екскрементів C. capreolus. Виявлено нормалізацію вмісту альбумінів при залученні екскрементів С. capreolus при 1 та 5 ГДК Cd відносно контролів. За умов 10 ГДК Cd інгібіювався нітратний обмін на 50% на фоні екскретів як C. capreolus, так і S. scrofa відносно контролю (контроль 10 ГДК Cd). Eкскреції S. scrofa порівняно із C. capreolus сприяли відновленню на 10% вмісту альбумінів відносно контролю. З’ясовано доцільність використання різних представників зооценозу для комплексного регулювання змін навколишнього середовища в умовах Степу України. 

Effect of cadmium on selected physiological and morphological parameters in metallicolous and non-metallicolous populations of Echium vulgare L

Cadmium tolerance of three populations of Echium vulgare L., naturally occurring on two Zn-Pb waste deposits (metallicolous populations M1, M2) and on an uncontaminated site (non-metallicolous population, NM) was investigated. The plants were cultivated in hydroponics at 0, 5, 15, 30, or 50μM Cd for 14 days. Although Cd reduced the content of photosynthetic pigments indifferently in the three populations, plant growth parameters and root viability analyses confirmed different Cd tolerances decreasing in the order M1>M2>NM in the populations studied. Organic acids (tartrate, malate, citrate, succinate) were not responsible for the elevated Cd tolerance of the metallicolous populations, although malate and citrate might participate in Cd detoxification in the roots of the M1 and M2. Phytochelatin concentrations were higher in the roots of M1 and M2 populations of E. vulgare, suggesting their role in Cd detoxification and different Cd tolerances.