Hormesis, which describes the stimulatory effect of low doses of toxic substances on growth, is a well-known phenomenon in the plant and animal kingdoms. However, the mechanisms that are involved in this phenomenon are still poorly understood. We performed preliminary studies on corn coleoptile sections, which showed a positive correlation between the stimulation of growth by Cd or Pb and an increase in the auxin and H 2 O 2 content in the coleoptile sections. Subsequently, we grew corn seedlings in hydroponic culture and tested a wide range of Cd or Pb concentrations in order to determine hormetic growth stimulation. In these seedlings the gas exchange and the chlorophyll a fluorescence, as well as the content of chlorophyll, flavonol, auxin and hydrogen peroxide, were measured. We found that during the hormetic stimulation of growth, the response of the photosynthetic apparatus to Cd and Pb differed significantly. While the application of Cd mostly caused a decrease in various photosynthetic parameters, the application of Pb stimulated some of them. Nevertheless, we discovered that the common features of the hormetic stimulation of shoot growth by heavy metals are an increase in the auxin and flavonol content and the maintenance of hydrogen peroxide at the same level as the control plants.

Hyperaccumulation and hypertolerance of Trace Metal Elements (TME) like Cd and Zn are highly variable in pseudo-metallophytes species. In this study we compared the impact of high Cd or Zn concentration on the photosynthetic apparatus of the Arabidopsis arenosa and Arabidopsis halleri pseudo-metallophytes growing on the same contaminated site in Piekary Slaskie in southern Poland. Plants were grown in hydroponic culture for 6 weeks, and then treated with 1.0 mM Cd or 5.0 mM Zn for 5 days. Chlorophyll a fluorescence and pigment content were measured after 0, 1, 2, 3, 4, and 5 days in plants grown in control and exposed to Cd or Zn treatments. Moreover, the effect of TME excess on the level of oxidative stress and gas-exchange parameters were investigated. In both plant species, exposure to high Cd or Zn induced a decrease in chlorophyll and an increase in anthocyanin contents in leaves compared to the control condition. After 5 days Cd treatment, energy absorbance, trapped energy flux and the percentage of active reaction centers decreased in both species. However, the dissipated energy flux in the leaves of A. arenosa was smaller than in A. halleri . Zn treatment had more toxic effect than Cd on electron transport in A. halleri compared with A. arenosa . A. arenosa plants treated with Zn excess did not react as strongly as in the Cd treatment and a decrease only in electron transport flux and percentage of active reaction centers compared with control was observed. The two species showed contrasting Cd and Zn accumulation. Cd concentration was almost 3-fold higher in A. arenosa leaves than in A. halleri . On the opposite, A. halleri leaves contained 3-fold higher Zn concentration than A. arenosa . In short, our results showed that the two Arabidopsis metallicolous populations are resistant to high Cd or Zn concentration, however, the photosynthetic apparatus responded differently to the toxic effects.

In earlier ecophysiological studies that were conducted on Arabidopsis halleri plants, scientists focused on the mechanisms of Cd and Zn hyperaccumulation but did not take into consideration the environmental factors that can significantly affect the physiological responses of plants in situ. In this study, we investigated A. halleri that was growing on two nonmetalliferous and three metalliferous sites, which were characterized by different environmental conditions. We compared these populations in order to find differences within the metallicolous and nonmetallicolous groups that have not yet been investigated. The concentrations of several elements in the plant and soil samples also were investigated. To our knowledge, the concentration and fluorescence of chlorophyll were measured for A. halleri in situ for the first time. Our study confirmed the hyperaccumulation of Cd and Zn for each metallicolous population. For the metallicolous populations, the inhibition of parameters that describe the efficiency of the photosynthetic apparatus with increasing accumulations of heavy metals in the shoots also was observed. It was found that the nonmetallicolous plant populations from the summit of Ciemniak Mountain had larger antenna dimensions and chlorophyll content but a lower percentage of active reaction centers. To our knowledge, in this study, the internal high physiological diversity within the populations that inhabit metalliferous and nonmetalliferous sites is presented for the first time.

Pseudometallophytes are commonly used to study the evolution of metal tolerance and accumulation traits in plants. Within the Arabidopsis genus, the adaptation of Arabidopsis halleri to metalliferous soils has been widely studied, which is not the case for the closely related species Arabidopsis arenosa. We performed an in-depth physiological comparison between the A. halleri and A. arenosa populations from the same polluted site, together with the geographically close non-metallicolous (NM) populations of both species. The ionomes, growth, photosynthetic parameters and pigment content were characterized in the plants that were growing on their native site and in a hydroponic culture under Cd treatments. In situ, the metallicolous (M) populations of both species hyperaccumulated Cd and Zn. The NM population of A. halleri hyperaccumulated Cd and Zn while the NM A. arenosa did not. In the hydroponic experiments, the NM populations of both species accumulated more Cd in their shoots than the M populations. Our research suggests that the two Arabidopsis species evolved different strategies of adaptation to extreme metallic environments that involve fine regulation of metal homeostasis, adjustment of the photosynthetic apparatus and accumulation of flavonols and anthocyanins.

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The aim of this study was to investigate the effect of autochthonous microorganisms present in soil collected from heavy metal (HM) uncontaminated (Pb ≈ 59 mg kg −1 , Cd ≈ 0.4 mg kg −1 , Zn ≈ 191 mg kg −1 ), moderately (Pb ≈ 343 mg kg −1 , Cd ≈ 12 mg kg −1 , Zn ≈ 1876 mg kg −1 ), and highly (Pb ≈ 1586 mg kg −1 , Cd ≈ 57 mg kg −1 , Zn ≈ 3280 mg kg −1 ) contaminated sites on Zea mays elemental composition, physiological status, and growth parameters. For this purpose, half of the collected soil was sterilized and soil characterization was performed. After 45 days of cultivation, the presence of HM in the soil negatively affected photosynthesis and transpiration rates, relative chlorophyll content, anthocyanins index, chlorophyll fluorescence parameters, and content of oxidative stress products (H 2 O 2 and Malondialdehyde) of Zea mays , while soil sterilization had a positive effect on those parameters. Average percentage of colonization of root segments by arbuscular mycorrhiza fungi decreased with an increase of HM contamination in the soil. The increase in shoot concentration of HMs, particularly Cd and Zn, was a result of contaminated soils sterilization. Aboveground biomass of maize cultivated on sterilized soil was 3-fold, 1.5-fold, and 1.5-fold higher for uncontaminated, moderately contaminated and highly contaminated soils respectively when compared to nonsterilized soils. Contrary to our expectation, autochthonous microflora did not improve plant growth and photosynthetic performance; in fact, they had a negative effect on those processes although they did reduce concentration of HMs in the shoots grown on contaminated soils. Electronic supplementary material The online version of this article (10.1007/s11356-018-3923-9) contains supplementary material, which is available to authorized users.

The aim of the research was to compare the impact of short-term deprivation of selected macronutrients (Ca, K, Mg and P) on the photosynthetic characteristics, transpiration and pigment content in maize. The strongest inhibition of photosynthesis was caused by a deprivation of Mg, which was visible as a decrease in the photosynthetic and transpiration rates, stomatal conductance, photosystem II (PSII) performance, chlorophyll and flavonol content with a simultaneously increased content of anthocyanins. In the K-deprived plants, a decrease in the photosynthetic rate was observed. However, the transpiration rate and stomatal conductance did not differ significantly compared with the control. In the K-deprived plants, a decrease in chlorophyll and an increase in the anthocyanin content were also observed. We showed that Ca starvation resulted in a decrease in the photosynthetic and transpiration rates, stomatal conductance and PSII performance, while the pigment content was not significantly different compared with the control. In the case of P-deprived plants, we observed a decrease in the photosynthetic and transpiration rates. Interestingly, the inhibition of stomatal conductance was the strongest in the P-deprived plants compared with all of the investigated elements. However, the performance of PSII was not significantly affected by P starvation compared with the control. Our results present for the first time a comprehensive analysis of the effect of short-term macronutrient deprivation on photosynthesis and transpiration in maize plants.

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