Hélène Dailly’s research while affiliated with Catholic University of Louvain and other places

Atriplex halimus L. is a promising xero-halophyte species for phytoremediation purposes but displays high levels of genetic variability. As an attempt to select uniform material suitable for phytomanagement, five clones were established by cuttings from three non-polluted sites (Tunis, Nabeul and Sfax), one moderately Pb-polluted site (Sousse) and a highly polymetallic polluted mining site (Gafsa). Cuttings were cultivated during 90 days under controlled conditions on soil issued from the most polluted area. The clone from Gafsa accumulated higher concentrations of metals in roots (Cr) and leaves (Cd, Sr, Zn and Cu) than other clones. Gafsa showed the highest absorption efficiency, translocation factor, bioconcentration factor and bioaccumulation coefficient compared to other clones but displayed the lowest relative growth rate (RGR) value while the highest RGR was found in the clone from Sousse. Heavy metal tolerance in Gafsa was not related to a more efficient management of oxidative stress or higher concentration of phytochelatins. Total amount of Sr and Zn removed from the substrate was the highest for Sousse while removal of Cd, Cu, Cr and Ni was the highest for Gafsa. It is concluded that cuttings allow to obtain uniform material for phytoremediation by Atriplex halimus and that combining different clones with complementary properties is an attractive option for phytomanagement of polymetallic polluted soils by this species.

Salt stress is a major environmental challenge for plants, leading to various physiological and biochemical responses. This study investigates the impact of salt stress on lipid peroxidation, phenolic and flavonoid accumulation, free-radical scavenging antioxidant activity, glutathione content, tocopherol levels in three amaranth (Amaranthus caudatus L) genotypes: Red Cascade (Red), Green Cascade (Green), and Pony Tail Mixed (Pony). The results showed that, under salt stress, lipid peroxidation increased, causing cell membrane damage and compromising cell integrity. However, salt stress also triggered the accumulation of phenolic and flavonoid compounds, which possess strong antioxidant properties and play a crucial role in scavenging reactive oxygen species. The total antioxidant activity as measured by DPPH inhibition was significantly enhanced in all genotypes under salt stress, with the Green genotype showing the highest activity. Additionally, salt stress induced an increase in total glutathione levels, maintaining the GSH/GSSG ratio relatively constant in all genotypes. However, tocopherol content decreased significantly under salt stress, with the Green genotype being the most affected. Finally, as membrane compounds are affected by oxidative stress, an analysis of membrane trafficking in root epidermal cells revealed that the Pony genotype had the highest response of the three genotypes. Overall, these findings suggest that salt stress induces complex responses in A. caudatus genotypes, involving oxidative damage, phenolic and flavonoid accumulation, enhanced antioxidant activity, and alterations in tocopherols and enhanced membrane trafficking. Understanding these responses can contribute to the development of salt-tolerant crops and improve agricultural productivity under saline conditions.

Miscanthus x giganteus is often considered as a suitable plant species for phytomanagement of heavy metal polluted sites. Nevertheless, its physiological behavior in response to the level of metal toxicity throughout the growing season remains poorly documented. Miscanthus x giganteus was cultivated on three sites in Belgium (BSJ: non-polluted control; CAR: slightly contaminated; VM strongly polluted by Cd, Pb, Cu, Zn, Ni and As). The presence of Miscanthus improved soil biological parameters assessed by measurement of enzyme activity and basal soil respiration on the three considered sites, although to a lower level on VM site. Heavy metal accumulation in the shoot was already recorded in spring. It displayed a contrasting distribution in the summer leaves since heavy metals and As metalloid accumulated mainly in the older leaves of CAR plants while showing a uniform distribution among leaves of different ages in VM plants. Comparatively to plants growing on BSJ, net photosynthesis decreased in plants growing on CAR and VM sites. The recorded decrease was mainly related to stomatal factors in CAR plants (decrease in stomatal conductance and in Ci) but to non-stomatal factors such as decrease in carboxylation efficiency and non-photochemical quenching in VM plants. Stomata remained open in VM plants which presented lower instantaneous and intrinsic water use efficiencies than CAR and BSJ plants. High proportions of heavy metals accumulated in CAR plants were bound to the cell wall fraction while the soluble and organelle-rich fractions were proportionally higher in VM plants, leading to a decrease in cell viability and cell membrane damages. It is concluded that not only the intensity but also the nature of physiological responses in Miscanthus x giganteus may drastically differ depending on the pollution level.

Glyphosate is one of the most widely used herbicides in the world. In addition to its herbicidal effect, glyphosate is a chelating agent that can form complexes with trace elements. Yet, agricultural soils can be contaminated with both organic and mineral substances, questioning the possible influence of glyphosate application on the trace element mobility. In this context, we specifically studied the extractability of trace elements in uncontaminated and metal-contaminated agricultural soils by adding glyphosate, formulated glyphosate, and aminomethylphosphonic acid (AMPA, a degradation product of glyphosate) in batch experiments from 0 to 100 mg L⁻¹. Results showed that, on average, glyphosate enhanced the extractability of the elements considered (e.g., As, Cd, Cu, Pb, and Zn) at 20 and 100 mg L⁻¹. Surprisingly, the uncontaminated soil highlighted the highest influence of glyphosate compared to the contaminated ones, likely resulting from a higher natural element extractability in the contaminated soils. Although formulated glyphosate presented an overall higher impact than unformulated glyphosate, it was evidenced that AMPA showed lower influence meaning that glyphosate degradation is beneficial to limit deleterious effects.

Climate change has intensified tomato plant infection by pathogens such as Pseudomonas syringae pv. tomato (Pst). Rootstocks may increase plant tolerance to leaf phytopathogens. The aim of this study was to evaluate the effects of the tolerant Poncho Negro (R) tomato rootstock on the physiological defence and the role of H2S in susceptible Limachino (L) tomato plant responses to Pst attack. Ungrafted (L), self-grafted (L/L) and grafted (L/R) plants were infected with Pst. Rootstock increased the antioxidant compounds including ascorbate in the scion. Tolerant rootstock induced an increase of H2S in the scion of the plants, which correlated with an enhanced expression of the SlAPX2 gene. A high accumulation of salicylic acid was observed in both Pst inoculated grafted plants, but in higher levels in L/R plant. The increase of H2S during bacterial infection was associated with a reduction of ethylene in L/R plants. Our study indicated that the rootstock reduced the damage of the bacterial speck disease in the Limachino tomato plants, conferring tolerance to bacterial infection. This study provides new knowledge of the impact of rootstock in the defence of tomato plants to leaf pathogens for sustainable management of tomato cultivation.

Upon permafrost thaw, the volume of soil accessible to plant roots increases which modifies the acquisition of plant-available resources. Tundra vegetation is actively responding to the changing environment with two major directions for vegetation shift across the Arctic: the expansion of deep-rooted sedges and the widespread increase in shallow-rooted shrubs. Changes in vegetation composition, density and distribution have large implications on the Arctic warming and permafrost stability by influencing the albedo, the snow accumulation and the litter decomposition rate. A better understanding of these cumulated effects of changing vegetation on warming and permafrost requires assessing the changes in plant nutrient sources upon permafrost thaw, nutrient access being a limiting factor for the Arctic tundra vegetation development. In this study, we determined the influence of permafrost degradation on the base cation sources for plant uptake by using the radiogenic Sr isotope ratio as a tracer of source, along a permafrost thaw gradient at Eight Mile Lake in Interior Alaska (USA). As plants take up Sr from the exchangeable soil fraction with no measurable fractionation, we determined the differences in ⁸⁷Sr/⁸⁶Sr ratio of the exchangeable Sr between shallow and deeper soil horizons, and we compared the ⁸⁷Sr/⁸⁶Sr ratio of foliar samples for three Arctic tundra species with contrasted rooting depths (Betula nana, Vaccinium vitis-idaea, and Eriophorum vaginatum) upon different permafrost thaw conditions. The higher foliar ⁸⁷Sr/⁸⁶Sr ratios of shallow-rooted Arctic tundra shrubs (B. nana, V. vitis-idaea) was consistent with a shallow source of soil exchangeable Sr from surface soil horizons, whereas the lower foliar ⁸⁷Sr/⁸⁶Sr ratios of deep-rooted Arctic tundra sedges (E. vaginatum) reflected a source of Sr from deeper soil horizons. There is a shift between poorly and highly thawed soil profiles towards lower foliar ⁸⁷Sr/⁸⁶Sr ratios in both deep- and shallow-rooted plant species. This shift supports that micro-landscape variability in the exchangeable base cation reserve with soil depth represents a key source of readily available nutrients for both shallow- and deep-rooted plant species upon permafrost thaw. This study highlights a key change in plant nutrient source to consider upon thaw. This finding lies beyond the common view that nutrient release at the permafrost thaw front preferentially benefits deep-rooted plant species.

The potato (Solanum tuberosum) is the fourth most important crop in the world. In Chile, its production is concentrated between the Bio Bio region and Los Lagos region. Climate change will increase, so it is extremely important to carry out an antioxidant and molecular characterization of various potato varieties, in order to evaluate their possible behavior against abiotic stresses such as water deficit and UV-B radiation. In this study, three native potato varieties and two commercial potato varieties were characterized, growing under field conditions. Leaf concentrations of polyphenols, ascorbate and malondialdehyde were quantified by spectrophotometry, leaf concentration of glutathione was quantified by HPLC and the expression of antioxidant genes was analyzed by semi-quantitative reverse transcription PCR. NG-30 variety showed the lowest flavonoid concentration, while Chona Negra and Desiree varieties showed the highest. The same pattern is repeated for the total anthocyanin and polyphenols content. There was no significant variation between varieties for the partial ascorbate content, and Desiree showed the lowest total ascorbate concentration and Patagonia-INIA, the highest. The total and reduced glutathione content was higher in Chona Negra, while the NG-30 variety showed the lowest glutathione values. NG-17 variety showed an intermediate profile in polyphenols, ascorbate and glutathione. The malondialdehyde content did not vary between the studied varieties. The expression of genes involved in antioxidant metabolism was correlated with the content of antioxidant molecules. We concluded the varieties Chona Negra and Desiree showed a good polyphenol profile and Chona Negra and Patagonia-INIA showed a good ascorbate and glutathione profile.

Salinity is one of the major abiotic stress limiting rice production in many areas of the world. The physiological drought due to low osmotic potential of soil solution and metabolic disorders caused by the high accumulation of toxic ions are the main constraints induced by salinity on plants. Among the major types of salinity, sodium chloride is predominant worldwide (Chinnusamy et al., 2005). As some area, however, are affected by an excess of sulfate salts, we compared the behaviour of rice facing NaCl and Na 2 SO 4 toxicities by exposing two contrasted rice cultivars (I Kong Pao: salt-sensitive and Pokkali: salt-resistant) to iso-strength Na + nutrient solutions at young seedling stage.

In field conditions, soil salinity may be due to an excess of different soluble salts. In order to compare the impact of chloride and sulfate salinities on rice, two contrasted cultivars (IKP: salt-sensitive and Pokkali: salt-resistant) were exposed to iso-strength Na⁺ nutrient solutions (NaCl 50 mM or Na2SO4 25 mM; EC: 5.31 dS m⁻¹) for 2 weeks under controlled environmental conditions. It was found that NaCl was more toxic than Na2SO4, especially for the salt-sensitive IKP. Sodium and proline accumulation were higher while shoot osmotic potential was lower in NaCl-treated plants than in those exposed to Na2SO4. Chloride-treated plants exhibited a higher shoot malondialdehyde concentration, suggesting a higher level of lipid peroxidation while Na2SO4-treated plants presented a slightly higher total antioxidant activity. Pokkali was more tolerant than IKP to both types of toxicities although it accumulated similar concentration of toxic ions. Pokkali was able to reduce the root osmotic potential and to quickly recycle oxidized glutathione to reduced glutathione, which may help the plant to more efficiently control its oxidative status in stress conditions. It is concluded that different salts may have distinct impacts on the plant physiology and that differences may vary according to the considered cultivar.

Background and aim Cichorium intybus is a biennal species storing inulin in taproot during the first year and flowering after vernalization. Heat impact on sugar distribution and inulin yield remains poorly documented. Methods Plants were cultivated under ambient or high (ambient+5 °C) temperature for 27 weeks. Plants were monthly harvested and morphological parameters, bolting rate, sugar translocation, soluble sugars and inulin content were determined. Results Heat reduced shoot and root growth and unexpectedly induced precocious bolting. It increased fructose contents in roots and leaves, increased root myo-inositol and reduced leaf sucrose content. At harvest, inulin content was higher in heat-treated than in control roots but total amount of inulin produced per plant was lower. Heat inhibited sugar translocation from leaves to secondary roots. Total soluble sugar content was lower in leaves but higher in roots of bolted plants compared to non-bolted ones. Bolting induced an increase in the mean degree of polymerization of inulin and root lignification. Conclusion High temperatures impaired inulin production as a result of root growth inhibition and reduced sugar translocation from the leaves to the roots. Heat induced precocious bolting on non-vernalized plants. Bolting reinforced root growth inhibition and thus inulin yield decrease.