The sugar beet gene encoding the sodium/proton exchanger 1 (BvNHX1) is regulated by a MYB transcription factor

Sodium/proton exchangers (NHX) are key players in the plant response to salinity and have a central role in establishing ion homeostasis. NHXs can be localized in the tonoplast or plasma membranes, where they exchange sodium ions for protons, resulting in sodium ions being removed from the cytosol into the vacuole or extracellular space. The expression of most plant NHX genes is modulated by exposure of the organisms to salt stress or water stress. We explored the regulation of the vacuolar NHX1 gene from the salt-tolerant sugar beet plant (BvNHX1) using Arabidopsis plants transformed with an array of constructs of BvHNX1::GUS, and the expression patterns were characterized using histological and quantitative assays. The 5′ UTR of BvNHX1, including its intron, does not modulate the activity of the promoter. Serial deletions show that a 337 bp promoter fragment sufficed for driving activity that indistinguishable from that of the full-length (2,464 bp) promoter. Mutating four putative cis-acting elements within the 337 bp promoter fragment revealed that MYB transcription factor(s) are involved in the activation of the expression of BvNHX1 upon exposure to salt and water stresses. Gel mobility shift assay confirmed that the WT but not the mutated MYB binding site is bound by nuclear protein extracted from salt-stressed Betavulgaris leaves

Analysis of salinity tolerance of Vitis vinifera 'Thompson Seedless' transformed with AtNHX1

Several transgenic plant species expressing AtNHX1, coding for a vacuolar Na+/H+ antiporter from Arabidopsis thaliana, have shown their ability to cope with salinity. The aim of this study was to analyze the response of Vitis vinifera cv. 'Thompson Seedless' transformed with AtNHX1 to salt stress, using soil substrate or hydroponic media, and to compare the response with untransformed 'Thompson Seedless' and allegedly tolerant 'Criolla' cultivars: 'Pedro Giménez' and 'Criolla Chica'. 'Thompson Seedless' embryogenic calli were transformed with Agrobacterium tumefaciens carrying AtNHX1 under the control of CaMV 35S promoter. Transgenic and untransformed plants were grown in a greenhouse under hydroponics or in pots with soil, and were subjected to increasing concentrations of sodium chloride (NaCl) up to 150 mM for a period of 7 weeks. Growth and toxicity symptoms were less affected in transgenics as compared to the untransformed grapevines, and transgenic lines had higher shoot length, leaf area and dry weights at the end of the experiment. Root concentrations of Na in transgenics were similar or lower than that observed in untransformed genotypes. Growth impairment and toxicity symptoms were observed in all genotypes under both conditions, but effects were more severe in plants growing with hydroponic culture. Potassium content and shoot to root dry weight ratio decreased with NaCl in hydroponics but not in pots. 'Criolla' cultivars grew less than the other genotypes, although 'Pedro Giménez' always exhibited highest shoot/root ratios

Ionic and osmotic relations in quinoa (Chenopodium quinoa Willd.) plants grown at various salinity levels

Ionic and osmotic relations in quinoa (Chenopodium quinoa Willd.) were studied by exposing plants to six salinity levels (0–500 mM NaCl range) for 70 d. Salt stress was administered either by pre-mixing of the calculated amount of NaCl with the potting mix before seeds were planted or by the gradual increase of NaCl levels in the irrigation water. For both methods, the optimal plant growth and biomass was achieved between 100 mM and 200 mM NaCl, suggesting that quinoa possess a very efficient system to adjust osmotically for abrupt increases in NaCl stress. Up to 95% of osmotic adjustment in old leaves and between 80% and 85% of osmotic adjustment in young leaves was achieved by means of accumulation of inorganic ions (Na+, K+, and Cl–) at these NaCl levels, whilst the contribution of organic osmolytes was very limited. Consistently higher K+ and lower Na+ levels were found in young, as compared with old leaves, for all salinity treatments. The shoot sap K+ progressively increased with increased salinity in old leaves; this is interpreted as evidence for the important role of free K+ in leaf osmotic adjustment under saline conditions. A 5-fold increase in salinity level (from 100 mM to 500 mM) resulted in only a 50% increase in the sap Na+ content, suggesting either a very strict control of xylem Na+ loading or an efficient Na+ removal from leaves. A very strong correlation between NaCl-induced K+ and H+ fluxes was observed in quinoa root, suggesting that a rapid NaCl-induced activation of H+-ATPase is needed to restore otherwise depolarized membrane potential and prevent further K+ leak from the cytosol. Taken together, this work emphasizes the role of inorganic ions for osmotic adjustment in halophytes and calls for more in-depth studies of the mechanisms of vacuolar Na+ sequestration, control of Na+ and K+ xylem loading, and their transport to the shoot

An isopentenyl transferase transgenic wheat isoline exhibits less seminal root growth impairment and a differential metabolite profile under Cd stress

Cadmium is one of the most important contaminants and it induces severe plant growth restriction. In this study, we analyzed the metabolic changes associated with root growth restriction caused by cadmium in the early seminal root apex of wheat. Our study included two genotypes: the commercial variety ProINTA Federal (WT) and the PSARK::IPT (IPT) line which exhibit high-grade yield performance under water deficit. Root tips of seedlings grown for 72 h without or with 10 μM CdCl2 (Cd-WT and Cd-IPT) were compared. Root length reduction was more severe in Cd-WT than Cd-IPT. Cd decreased superoxide dismutase activity in both lines and increased catalase activity only in the WT. In Cd-IPT, ascorbate and guaiacol peroxidase activities raised compared to Cd-WT. The hormonal homeostasis was altered by the metal, with significant decreases in abscisic acid, jasmonic acid, 12-oxophytodienoic acid, gibberellins GA20, and GA7 levels. Increases in flavonoids and phenylamides were also found. Root growth impairment was not associated with a decrease in expansin (EXP) transcripts. On the contrary, TaEXPB8 expression increased in the WT treated by Cd. Our findings suggest that the line expressing the PSARK::IPT construction increased the homeostatic range to cope with Cd stress, which is visible by a lesser reduction of the root elongation compared to WT plants. The decline of root growth produced by Cd was associated with hormonal imbalance at the root apex level. We hypothesize that activation of phenolic secondary metabolism could enhance antioxidant defenses and contribute to cell wall reinforcement to deal with Cd toxicity

Fine mapping of the linkage group 2 drought tolerance QTL in pearl millet [Pennisetum glaucum (L.) R. Br.]

Pearl millet is an important cereal crop capable of growing in semi-arid, arid and marginal regions of the world. Drought is a major abiotic constraint affecting pearl millet production globally. Previously identified and validated major linkage group 2 (LG2) drought tolerance (DT) QTL contributing to hybrid grain and stover yield potential to terminal drought stress is being fine mapped. The fine mapping population was generated by crossing two near-isogenic lines (NILs) differing for the LG2 DT QTL. A modified double digest restriction site associated DNA (ddRAD) technique using SphI and MluCI enzyme combination was employed. A total of 290 out of 6,067 F2 mapping population of the cross (H77/833-2-P10 × ICMR 01029-P10), and parents were genotyped on Illumina HiSeq2500. Out of 52,028 SNPs that were identified from a total of 888.85 million reads at a read depth of 10 in the mapping population, a total of 6,821 SNPs were used for mapping. The genotypic data of these SNPs were used in combination with that of seven SSRs that had known linkage relationship with LG2 DT QTL interval. Linkage map was constructed using QTL IciMapping 4.1 software at a LOD threshold of 3.0. A total of 189 SNPs anchored to seven SSRs were mapped to the LG2 DT QTL. The length of linkage group (LG) was 639.72 cM (Haldane units) with an average inter-marker distance of 6.73 cM. In order to refine the fine mapping process, ddRAD technique is being further employed for genotyping rest of the fine mapping population