Interaction between Sulfate and Selenate in Tetraploid Wheat (Triticum turgidum L.) Genotypes.

Selenium (Se) is an essential micronutrient of fundamental importance to human health and the main Se source is from plant-derived foods. Plants mainly take up Se as selenate (SeO42-), through the root sulfate transport system, because of their chemical similarity. The aims of this study were (1) to characterize the interaction between Se and S during the root uptake process, by measuring the expression of genes coding for high-affinity sulfate transporters and (2) to explore the possibility of increasing plant capability to take up Se by modulating S availability in the growth medium. We selected different tetraploid wheat genotypes as model plants, including a modern genotype, Svevo (Triticum turgidum ssp. durum), and three ancient Khorasan wheats, Kamut, Turanicum 21, and Etrusco (Triticum turgidum ssp. turanicum). The plants were cultivated hydroponically for 20 days in the presence of two sulfate levels, adequate (S = 1.2 mM) and limiting (L = 0.06 mM), and three selenate levels (0, 10, 50 µM). Our findings clearly showed the differential expression of genes encoding the two high-affinity transporters (TdSultr1.1 and TdSultr1.3), which are involved in the primary uptake of sulfate from the rhizosphere. Interestingly, Se accumulation in shoots was higher when S was limited in the nutrient solution.

Differential modulation of Target of Rapamycin activity under single and combined iron and sulfur deficiency in tomato plants.

Over the past few decades, a close relationship between sulfur (S) and iron (Fe) in terms of functionality and nutrition was demonstrated in the tomato. However, very little is known about the regulatory mechanisms underlying S/Fe interactions. Recently, the potential role of citrate in plant adaptation to Fe deficiency and combined S and Fe deficiency has been described. It is known that an impaired organic acid metabolism may stimulate a retrograde signal, which has been proven to be linked to the Target of Rapamycin (TOR) signaling in yeast and animal cells. Recent reports provided evidence of TOR involvement in S nutrient sensing in plants. This suggestion prompted us to investigate whether TOR may play a role in the cross-talk of signaling pathway occurring during plant adaptation to combined nutrient deficiency of Fe and S. Our results revealed that Fe deficiency elicited an increase of TOR activity associated with enhanced accumulation of citrate. In contrast, S deficiency resulted in decreased TOR activity and citrate accumulation. Interestingly, citrate accumulated in shoots of plants exposed to combined S/Fe deficiency to values between those found in Fe- and S-deficient plants, again correlated with TOR activity level. Our results suggest that citrate might be involved in establishing a link between plant response to combined S/Fe deficiency and the TOR network.

Response of Olive Shoots to Salinity Stress Suggests the Involvement of Sulfur Metabolism.

Global warming has two dangerous global consequences for agriculture: drought, due to water scarcity, and salinization, due to the prolonged use of water containing high concentrations of salts. Since the global climate is projected to continue to change over this century and beyond, choosing salt-tolerant plants could represent a potential paramount last resort for exploiting the secondary saline soils. Olive is considered moderately resistant to soil salinity as compared to other fruit trees, and in the present study, we investigated the influence of NaCl solutions (ranging from 0 to 200 mM) in a salt-tolerant (cv Canino) and two of its transgenic lines (Canino AT17-1 and Canino AT17-2), overexpressing tobacco osmotin gene, and in a salt-sensitive (Sirole) olive cultivar. After four weeks, most of the shoots of both Canino and Sirole plants showed stunted growth and ultimate leaf drop by exposure to salt-enriched media, contrary to transgenic lines, that did not show injuries and exhibited a normal growth rate. Malondialdehyde (MDA) content was also measured as an indicator of the lipid peroxidation level. To evaluate the role of the S assimilatory pathway in alleviating the adverse effects of salt stress, thiols levels as well as extractable activities of ATP sulfurylase (ATPS) and O-acetyl serine(thiol)lyase (OASTL), the first and the last enzyme of the S assimilation pathway, respectively, have been estimated. The results have clearly depicted that both transgenic lines overexpressing osmotin gene coped with increasing levels of NaCl by the induction of S metabolism, and particularly increase in OASTL activity closely paralleled changes of NaCl concentration. Linear correlation between salt stress and OASTL activity provides evidence that the S assimilation pathway plays a key role in adaptive response of olive plants under salt stress conditions.

Single and Combined Fe and S Deficiency Differentially Modulate Root Exudate Composition in Tomato: A Double Strategy for Fe Acquisition?

Fe chlorosis is considered as one of the major constraints on crop growth and yield worldwide, being particularly worse when associated with S shortage, due to the tight link between Fe and S. Plant adaptation to inadequate nutrient availabilities often relies on the release of root exudates that enhance nutrients, mobilization from soil colloids and favour their uptake by roots. This work aims at characterizing the exudomic profile of hydroponically grown tomato plants subjected to either single or combined Fe and S deficiency, as well as at shedding light on the regulation mechanisms underlying Fe and S acquisition processes by plants. Root exudates have been analysed by untargeted metabolomics, through liquid chromatography-mass spectrometry as well as gas chromatography-mass spectrometry following derivatization. More than 200 metabolites could be putatively annotated. Venn diagrams show that 23%, 10% and 21% of differential metabolites are distinctively modulated by single Fe deficiency, single S deficiency or combined Fe-S deficiency, respectively. Interestingly, for the first time, a mugineic acid derivative is detected in dicot plants root exudates. The results seem to support the hypothesis of the co-existence of the two Fe acquisition strategies in tomato plants.

Evaluating the potential use of Cu-contaminated soils for giant reed (Arundo donax, L.) cultivation as a biomass crop.

Over the past decades, the important topic of environmental sustainability, impact, and security of the fossil fuel supply has stimulated interest in using lignocellulosic feedstocks as biofuel to partially cover energy demands. Among energy no-food crops, giant reed (Arundo donax, L.), a perennial rhizomatous grass has been identified as a leading candidate crop for lignocellulosic feedstock, due to its positive energy balance, and low ecological/agro-management demands. The aim of the present study was to characterize the physiological response of Arundo donax (L.) to artificial soil contamination with three different Cu levels (200, 400, and 800 ppm), and to assess the relationship between plant Cu tolerance and S assimilation rate. The present study not only confirms the ability of Arundo donax L. to cope with Cu stress and therefore to grow in marginal, degraded lands abandoned by mainstream agricultural, but also shows that plant performance might be likely ascribed to a modulation of sulfate metabolism resulting in increased thiols content.

Revisiting Fe/S interplay in tomato: A split-root approach to study the systemic and local responses.

Based on our previous studies demonstrating an intriguing interplay between sulfur (S) and iron (Fe), a split-root experiment was performed to determine whether plant S status and/or S external concentration could modify plant capability to take up and accumulate Fe. This split-root system allowed the roots of each tomato plant to grow in two different compartments, both Fe-deficient, but one S-sufficient, and the other one S-free. Although S was freely available to half root system and thus plant S status was preserved, S-deficient part of root apparatus exhibited a decrease of total S, thiols and protein content, an enhanced activity of both ATPsulfurylase and O-acetylserine(thiol)lyase, and a higher expression of SlST1.1, as occurring under S deficiency. The side of the root apparatus exposed to combined S and Fe deficiency, showed an over induction of the FeIII-reducing capacity (+40%) and of the expression levels of the gene codifying for this protein (SlFRO1), with respect to the Fe-deficient part of the root system. Interestingly, the regulation pattern of the bHLH transcription factor SlFER, controlling the expression of both SlFRO1 and SlIRT1 genes, was very close to that of SlFRO1. SlIRT1 expression levels appeared unaffected by S supply, suggesting distinct regulatory processes targeting SlFRO1 and SlIRT1.