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Plant hormones are important in the control of physiological and developmental processes including seed germination, senescence, flowering, stomatal aperture, and ultimately the overall growth and yield of plants. Many currently available methods to quantify such growth regulators quickly and accurately require extensive sample purification using complex analytic techniques. Herein we used ultra-performance liquid chromatography-high-resolution mass spectrometry (UHPLC-HRMS) to create and validate the prediction of hormone concentrations made using attenuated total reflection Fourier-transform infrared (ATR-FTIR) spectral profiles of both freeze-dried ground leaf tissue and extracted xylem sap of Japanese knotweed (Reynoutria japonica) plants grown under different environmental conditions. In addition to these predictions made with partial least squares regression, further analysis of spectral data was performed using chemometric techniques, including principal component analysis, linear discriminant analysis, and support vector machines (SVM). Plants grown in different environments had sufficiently different biochemical profiles, including plant hormonal compounds, to allow successful differentiation by ATR-FTIR spectroscopy coupled with SVM. ATR-FTIR spectral biomarkers highlighted a range of biomolecules responsible for the differing spectral signatures between growth environments, such as triacylglycerol, proteins and amino acids, tannins, pectin, polysaccharides such as starch and cellulose, DNA and RNA. Using partial least squares regression, we show the potential for accurate prediction of plant hormone concentrations from ATR-FTIR spectral profiles, calibrated with hormonal data quantified by UHPLC-HRMS. The application of ATR-FTIR spectroscopy and chemometrics offers accurate prediction of hormone concentrations in plant samples, with advantages over existing approaches. [ABSTRACT FROM AUTHOR]

The current investigation aims to underline the impact of salicylic acid or calcium chloride seed pre-treatments on mineral status and oxidative stress markers, namely levels of electrolyte leakage (EL) and lipid peroxidation levels, measured as thiobarbituric reactive substances (TBARS), and the activity of some antioxidant enzymes in roots and leaves of plants in two barley species grown under various salt treatments. Overall, our results revealed that salinity inhibits essential nutrient absorption such as iron, calcium, magnesium and potassium and stimulates the absorption of sodium. Also, this environmental constraint induced oxidative stress in plants in comparison with the control conditions. This state of oxidative stress is reflected by an increase in TBARS content as well as the stimulation of EL values. In addition, salinity induced disturbances in the activity of antioxidant enzymes, which were mainly dependent on the applied salt concentration and the species. In addition, Hordeum marinum maintained high antioxidant enzyme activity and low levels of oxidative stress parameters, which reinforces its salt-tolerant character. Importantly, salicylic acid or calcium chloride seed priming alleviated the mineral imbalance and the oxidative damage induced by salinity. Moreover, seed priming improves iron, calcium magnesium and potassium content and limitsthe accumulation of sodium. Also, both treatments not only decrease TBARS levels and limit EL, but they also stimulate the antioxidant enzyme activities in the leaves and roots of the stressed plants as compared with stressed plants grown from non-primed seeds. Interestingly, the beneficial effects of the mentioned treatments were more notable on Hordeum vulgare species. [ABSTRACT FROM AUTHOR]

Many highly valued chemicals in the pharmaceutical, biotechnological, cosmetic, and biomedical industries belong to the terpenoid family. Biosynthesis of these chemicals relies on polymerization of Isopentenyl di-phosphate (IPP) and/or dimethylallyl diphosphate (DMAPP) monomers, which plants synthesize using two alternative pathways: a cytosolic mevalonic acid (MVA) pathway and a plastidic methyleritritol-4-phosphate (MEP) pathway. As such, developing plants for use as a platform to use IPP/DMAPP and produce high value terpenoids is an important biotechnological goal. Still, IPP/DMAPP are the precursors to many plant developmental hormones. This creates severe challenges in redirecting IPP/DMAPP towards production of non-cognate plant metabolites. A potential solution to this problem is increasing the IPP/ DMAPP production flux in planta. Here, we aimed at discovering, understanding, and predicting the effects of increasing IPP/DMAPP production in plants through modelling. We used synthetic biology to create rice lines containing an additional ectopic MVA biosynthetic pathway for producing IPP/DMAPP. The rice lines express three alternative versions of the additional MVA pathway in the plastid, in addition to the normal endogenous pathways. We collected data for changes in macroscopic and molecular phenotypes, gene expression, isoprenoid content, and hormone abundance in those lines. To integrate the molecular and macroscopic data and develop a more in depth understanding of the effects of engineering the exogenous pathway in the mutant rice lines, we developed and analyzed data-centric, line-specific, multilevel mathematical models. These models connect the effects of variations in hormones and gene expression to changes in macroscopic plant phenotype and metabolite concentrations within the MVA and MEP pathways of WT and mutant rice lines. Our models allow us to predict how an exogenous IPP/DMAPP biosynthetic pathway affects the flux of terpenoid precursors. We also quantify the long-term effect of plant hormones on the dynamic behavior of IPP/DMAPP biosynthetic pathways in seeds, and predict plant characteristics, such as plant height, leaf size, and chlorophyll content from molecular data. In addition, our models are a tool that can be used in the future to help in prioritizing re-engineering strategies for the exogenous pathway in order to achieve specific metabolic goals. [ABSTRACT FROM AUTHOR]

Teak (Tectona grandis) is one of the most important wood sources, and it is cultivated in tropical regions with a significant market around the world. Abiotic stresses are an increasingly common and worrying environmental phenomenon because it causes production losses in both agriculture and forestry. Plants adapt to these stress conditions by activation or repression of specific genes, and they synthesize numerous stress proteins to maintain their cellular function. For example, APETALA2/ethylene response factor (AP2/ERF) was found to be involved in stress signal transduction. A search in the teak transcriptome database identified an AP2/ERF gene named TgERF1 with a key AP2/ERF domain. We then verified that the TgERF1 expression is rapidly induced by Polyethylene Glycol (PEG), NaCl, and exogenous phytohormone treatments, suggesting a potential role in drought and salt stress tolerance in teak. The full-length coding sequence of TgERF1 gene was isolated from teak young stems, characterized, cloned, and constitutively overexpressed in tobacco plants. In transgenic tobacco plants, the overexpressed TgERF1 protein was localized exclusively in the cell nucleus, as expected for a transcription factor. Furthermore, functional characterization of TgERF1 provided evidence that TgERF1 is a promising candidate gene to be used as selective marker on plant breeding intending to improve plant stress tolerance. [ABSTRACT FROM AUTHOR]

(1) Background: Peach cv. GF305 is commonly used in breeding programs due to its susceptibility to numerous viruses. In this study, we aimed to achieve a methodology for rapid and uniform seed germination of peach cv. GF305 in order to obtain vigorous seedlings; (2) Methods: A combination of cold stratification and H2O2 imbibition was tested on peach seeds with or without endocarp. In addition, the levels of non-enzymatic antioxidants ascorbate and glutathione as well as the hormone profile in seedling roots and shoots were determined; (3) Results: We found that H2O2 imbibition of peach seeds without endocarp after 8 weeks of stratification increased germination rate and resulted in seedlings displaying good vegetative growth. The H2O2 imbibition also affected the levels of ascorbate, glutathione, and the phytohormones abscisic acid and jasmonic acid in peach seedlings; (4) Conclusions: Although stratification periods of 12 weeks have been previously established as being appropriate for this cultivar, we have been able to reduce this stratification time by up to 4 weeks, which may have practical implication in peach nurseries. [ABSTRACT FROM AUTHOR]

To determine whether root‐supplied ABA alleviates saline stress, tomato (Solanum lycopersicum L. cv. Sugar Drop) was grafted onto two independent lines (NCED OE) overexpressing the SlNCED1 gene (9‐cis‐epoxycarotenoid dioxygenase) and wild type rootstocks. After 200 days of saline irrigation (EC = 3.5 dS m−1), plants with NCED OE rootstocks had 30% higher fruit yield, but decreased root biomass and lateral root development. Although NCED OE rootstocks upregulated ABA‐signalling (AREB, ATHB12), ethylene‐related (ACCs, ERFs), aquaporin (PIPs) and stress‐related (TAS14, KIN, LEA) genes, downregulation of PYL ABA receptors and signalling components (WRKYs), ethylene synthesis (ACOs) and auxin‐responsive factors occurred. Elevated SlNCED1 expression enhanced ABA levels in reproductive tissue while ABA catabolites accumulated in leaf and xylem sap suggesting homeostatic mechanisms. NCED OE also reduced xylem cytokinin transport to the shoot and stimulated foliar 2‐isopentenyl adenine (iP) accumulation and phloem transport. Moreover, increased xylem GA3 levels in growing fruit trusses were associated with enhanced reproductive growth. Improved photosynthesis without changes in stomatal conductance was consistent with reduced stress sensitivity and hormone‐mediated alteration of leaf growth and mesophyll structure. Combined with increases in leaf nutrients and flavonoids, systemic changes in hormone balance could explain enhanced vigour, reproductive growth and yield under saline stress. ABA overproducing tomato rootstocks increase shoot vigour and fruit yield under saline conditions by altering stress‐related responses, improving photosynthesis and optimizing source‐sink relationships. [ABSTRACT FROM AUTHOR]

The agriculture industry is frequently affected by various abiotic stresses limiting plant productivity. To decrease the negative effect of salinity and improve growth performance, some strategies have been used, such as exogenous application of plant growth regulators (i.e. gibberellic acid, GA 3 ), or arbuscular mycorrhizal fungi (AMF) inoculation. To gain insights about the cross-talk effect of exogenous GA 3 application and AMF inoculation on growth under salinity conditions, tomato plants ( Solanum lycopersicum, cv. TT-115) were inoculated or not with the AMF Rhizophagus irregularis and exposed to different treatments during two weeks: 0 M GA 3 + 0 mM NaCl, 10 −6 M GA 3 + 0 mM NaCl, 0 M GA 3 + 100 mM NaCl and 10 −6 M GA 3 + 100 mM NaCl. Results have revealed that AMF inoculation or GA 3 application alone, but especially their interaction, resulted in growth improvement under salinity conditions. The growth improvement observed in AMF-inoculated tomato plants under salinity conditions was mainly associated to ionic factors (higher K concentration and K/Na ratio) while the alleviating effect of GA 3 application and its interaction with AMF appear to be due to changes in the hormonal balance. Foliar GA 3 application was found to increase the active gibberellins (GAs), resulting in a positive correlation between GA 3 and the growth-related parameters. Furthermore, cytokinins, indoleacetic acid and abscisic acid concentrations increased in AMF inoculated or GA 3 treated plants but, notably, in AMF plants treated with GA 3 , which showed improved growth under salinity conditions. This suggests that there is an interactive positive effect between GAs and AMF which alleviates growth impairment under salinity conditions by modifying the hormonal balance of the plant. [ABSTRACT FROM AUTHOR]

Grafting provides a tool aimed to increase low-P stress tolerance of crops, however, little is known about the mechanism (s) by which rootstocks can confer resistance to P deprivation. In this study, 4 contrasting groups of rootstocks from different genetic backgrounds (Solanum lycopersicum var. cerasiforme and introgression and recombinant inbred lines derived from the wild relatives S. pennellii and S. pimpinellifolium) were grafted to a commercial F1 hybrid scion and cultivated under control (1 mM, c) and P deficient (0.1 mM, p) conditions for 30 days, to analyze rootstocks-mediated traits that impart low (L, low shoot dry weight, SDW) or high (H, high SDW) vigor. Xylem sap ionic and hormonal anlyses leaf nutritional status suggested that some physiological traits can explain rootstocks impacts on shoot growth. Although xylem P concentration increased with root biomass under both growing conditions, shoot biomass under low-P was explained by neither changes in root growth nor P transport and assimilation. Indeed, decreased root P export only explained the sensitivity of the HcLp rootstocks, while leaf P status was similarly affected in all graft combinations. Interestingly, most of the nutrients analyzed in the xylem sap correlated with root biomass under standard fertilization but only Ca was consistently related to shoot biomass under both control and low-P, suggesting an important role for this nutrient in rootstock-mediated vigor. Moreover, foliar Ca, S, and Mn concentrations were (i) specifically correlated with shoot growth under low-P and (ii) positively and negatively associated to the root-to-shoot transport of the cytokinin trans-zeatin (t-Z) and the ethylene precursor 1-aminocyclopropane-1-carboxylic acid (ACC), respectively. Indeed, those hormones seem to play an antagonistic positive (t-Z) and negative (ACC) role in the rootstock-mediated regulation of shoot growth in response to P nutrition. The use of Hp-type rootstocks seems to enhance P use efficiency of a commercial scion variety, therefore could potentially be used for increasing yield and agronomic stability under low P availability. [ABSTRACT FROM AUTHOR]

Selection and breeding of rootstocks that can tolerate low K supply may increase crop productivity in low fertility soils and reduce fertilizer application. However, the underlying physiological traits are still largely unknown. In this study, 16 contrasting recombinant inbred lines (RILs) derived from a cross between domestic and wild tomato species (Solanum lycopersicum × Solanum pimpinellifolium) have been used to analyse traits related to the rootstock-mediated induction of low (L, low shoot fresh weight) or high (H, high shoot fresh weight) vigor to a commercial F1 hybrid grown under control (6 mM, c) and low-K (1 mM, k). Based on hormonal and ionomic composition in the root xylem sap and the leaf nutritional status after long-term (7 weeks) exposure low-K supply, a model can be proposed to explain the rootstocks effects on shoot performance with the ethylene precursor aminocyclopropane-1-carboxylic acid (ACC) playing a pivotal negative role. The concentration of this hormone was higher in the low-vigor Lc and Lk rootstocks under both conditions, increased in the sensitive HcLk plants under low-K while it was reduced in the high-vigor Hk ones. Low ACC levels would promote the transport of K vs. Na in the vigorous Hk grafted plants. Along with K, Ca, and S, micronutrient uptake and transport were also activated in the tolerant Hk combinations under low-K. Additionally, an interconversion of trans-zeatin into trans-zeatin riboside would contribute to decrease ACC in the tolerant LcHk plants. The high vigor induced by the Hk plants can also be explained by an interaction of ACC with other hormones (cytokinins and salicylic, abscisic and jasmonic acids). Therefore, Hk rootstocks convert an elite tomato F1 cultivar into a (micro) nutrient-efficient phenotype, improving growth under reduced K fertilization. [ABSTRACT FROM AUTHOR]

Abiotic stresses such as heat, drought or salinity have been widely studied individually. Nevertheless, in the nature and in the field, plants and crops are commonly exposed to a different combination of stresses, which often result in a synergistic response mediated by the activation of several molecular pathways that cannot be inferred from the response to each individual stress. By screening microarray data obtained from different plant species and under different stresses, we identified several conserved stress-responsive genes whose expression was differentially regulated in tomato (Solanum lycopersicum L.) roots in response to one or several stresses. We validated 10 of these genes as reliable biomarkers whose expression levels are related to different signalling pathways involved in adaptive stress responses. In addition, the genes identified in this work could be used as general salt-stress biomarkers to rapidly evaluate the response of salt-tolerant cultivars and wild species for which sufficient genetic information is not yet available. [ABSTRACT FROM AUTHOR]

Summary: Nitrogen availability is an important limiting factor for plant growth. Although NH4 + assimilation is energetically more favorable than NO3 −, it is usually toxic for plants. In order to study if an improved ammonium assimilatory metabolism could increase the plant tolerance to ammonium nutrition, tomato (Solanum lycopersicum L. cv P-73) plants were transformed with an NH4 +-dependent asparagine synthetase (AS-A) gene from Escherichia coli (asnA) under the control of a PCpea promoter (pea isolated constitutive promotor). Homozygous (Hom), azygous (Az) asnA and wild type (WT) plants were grown hydroponically for 6 weeks with normal Hoagland nutrition (NO3 −/NH4 + =6/0.5) and high ammonium nutrition (NO3 −/NH4 + =3.5/3). Under Hoagland''s conditions, Hom plants produced 40–50% less biomass than WT and Az plants. However, under NO3 −/NH4 + =3.5/3 the biomass of Hom was not affected while it was reduced by 40–70% in WT and Az plants compared to Hoagland, respectively. The Hom plants accumulated 1.5–4 times more asparagine, glycine, serine and soluble proteins and registered higher glutamine synthetase (GS) and glutamate synthase (GOGAT) activities in the light-adapted leaves than the other genotypes, but had similar NH4 + and NO3 − levels in all conditions. In the dark-adapted leaves, a protein catabolism occurred in the Hom plants with a concomitant 25–40% increase in organic acid concentration, while asparagine accumulation registered the highest values. The aforementioned processes might be responsible for a positive energetic balance as regards the futile cycle of the transgenic protein synthesis and catabolism. This explains growth penalty under standard nutrition and growth stability under NO3 −/NH4 + =3.5/3, respectively. [Copyright &y& Elsevier]

Germination and early seedling development are critical for successful stand establishment of plants. Following germination, the cotyledons, which are derived from embryonic tissue, emerge from the seed. Arabidopsis seedlings at post-germinative stages are supported mainly by the supply of nutrition from the cotyledons until vegetative leaves emerge and initiate photosynthesis. The switch to autotrophic growth is a significant transition at the post-germinative stage. Here, we provide evidence that down-regulation of SQUAMOSA PROMOTER-BINDING PROTEIN LIKE13 (SPL13) by microRNA156 (miR156) plays an important role in the regulation of the post-germinative switch from the cotyledon stage to the vegetative-leaf stage. Silent mutations created in the SPL13 sequence in the region that is complementary to the miR156 sequence caused the deregulation of the mutant form of SPL13 (mSPL13) mRNA from miR156. Mutant seedlings over-accumulated miRNA-resistant messages and exhibited a delay in the emergence of vegetative leaves compared to wild-type seedlings. The delay was not observed in control transgenic plants expressing nonmutated SPL13, indicating that the phenotype was caused specifically by the silent mutations and deregulation of SPL13 from miR156. Characterization of the SPL13 promoter indicated that this gene is expressed mainly in the hypocotyl and affects leaf primordium development. These results suggest that the repression of SPL13 by miR156 is essential for normal post-germinative growth in Arabidopsis. [ABSTRACT FROM AUTHOR]

MicroRNAs (miRNAs) are involved in developmental programmes of plants, including seed germination and post-germination. Here, we provide evidence that two different miRNA pathways, miR156 and miR172, interact during the post-germination stages in Arabidopsis. Mutant seedlings expressing miR156-resistant SQUAMOSA PROMOTER-BINDING PROTEIN-LIKE13 (mSPL13), which has silent mutations in the miR156 complementary sequence, over-accumulated SPL13 mRNA and exhibited a delay in seedling development. Microarray analysis indicated that SCHNARCHZAPFEN (SNZ), an AP2-like gene targeted by miR172, was downregulated in these mutants. Quantitative reverse transcription- polymerase chain reaction (RT-PCR) and miRNA gel blot analyses showed that the MIR172 genes were up-regulated in mSPL13 mutants. These results suggest that the miRNA regulation cascades (miR156 s SPL13 → miR172 ⊣ SNZ) play a critical role during the post-germination developmental stages in Arabidopsis. [ABSTRACT FROM AUTHOR]

Tomato crop productivity under salinity can be improved by grafting cultivars onto salt-tolerant wild relatives, thus mediating the supply of root-derived ionic and hormonal factors that regulate leaf area and senescence. A tomato cultivar was grafted onto rootstocks from a population of recombinant inbred lines (RILs) derived from a Solanum lycopersicum × Solanum cheesmaniae cross and cultivated under moderate salinity (75 mm NaCl). Concentrations of Na+, K+ and several phytohormones [abscisic acid (ABA); the cytokinins (CKs) zeatin, Z; zeatin riboside, ZR; and the ethylene precursor 1-aminocyclopropane-1-carboxylic acid (ACC)] were analysed in leaf xylem sap in graft combinations of contrasting vigour. Scion leaf area correlated with photosystem II (PSII) efficiency ( Fv/ Fm) and determined fruit productivity. Xylem K+ (but not Na+), K+/Na+, the active CK Z, the ratio with its storage form Z/ZR and especially the ratio between CKs and ACC (Z/ACC and Z + ZR/ACC) were positively loaded into the first principal component (PC) determining both leaf growth and PSII efficiency. In contrast, the ratio ACC/ABA was negatively correlated with leaf biomass. Although the underlying physiological mechanisms by which rootstocks mediate leaf area or chlorophyll fluorescence (and thus influence tomato salt tolerance) seem complex, a putative potassium–CK interaction involved in regulating both processes merits further attention. [ABSTRACT FROM AUTHOR]

The effect of short-term treatments (10 days) by a high salt level (150mmNaCl) on vegetative and reproductive development was investigated in tomato plants (Solanum lycopersicumL. cv. Ailsa Craig) at two developmental stages. Salinity applied during flowering transition reduced shoot biomass and delayed the appearance of the first inflorescence. Both shoot and root biomasses were reduced when salt was applied during the development of the first inflorescence. At both stages, areas of young leaves decreased and time to first anthesis increased, while total number of flowers in the first inflorescence was not affected. Flower abortion, reduction of pollen number and viability were higher when salinity was applied during inflorescence development. Na+accumulated in all organs while K+decreased. Laser ablation inductively coupled plasma mass spectrometry microanalysis revealed that Na+accumulated in style, ovaries and anther intermediate layers but not in the tapetum nor in the pollen grains when salinity was applied during inflorescence development. K+was not significantly affected in these structures. Soluble carbohydrates dramatically increased in leaves and decreased in the inflorescence under salt stress conditions. The failure of inflorescence to develop normally under salt stress can be better explained in terms of altered source–sink relationships rather than accumulation of toxic ions. [ABSTRACT FROM AUTHOR]

Plants have a remarkable regenerative capacity, which allows them to survive tissue damage after biotic and abiotic stresses. In this study, we use Solanum lycopersicum 'Micro-Tom' explants as a model to investigate wound-induced de novo organ formation, as these explants can regenerate the missing structures without the exogenous application of plant hormones. Here, we performed simultaneous targeted profiling of 22 phytohormone-related metabolites during de novo organ formation and found that endogenous hormone levels dynamically changed after root and shoot excision, according to region-specific patterns. Our results indicate that a defined temporal window of high auxin-to-cytokinin accumulation in the basal region of the explants was required for adventitious root formation and that was dependent on a concerted regulation of polar auxin transport through the hypocotyl, of local induction of auxin biosynthesis, and of local inhibition of auxin degradation. In the apical region, though, a minimum of auxin-to-cytokinin ratio is established shortly after wounding both by decreasing active auxin levels and by draining auxin via its basipetal transport and internalization. Cross-validation with transcriptomic data highlighted the main hormonal gradients involved in wound-induced de novo organ formation in tomato hypocotyl explants. [ABSTRACT FROM AUTHOR]

Plants have remarkable regenerative capacity, which allows them to survive tissue damage after exposure to biotic and abiotic stresses. Some of the key transcription factors and hormone crosstalk mechanisms involved in wound-induced organ regeneration have been extensively studied in the model plant Arabidopsis thaliana. However, little is known about the role of metabolism in wound-induced organ formation. Here, we performed detailed transcriptome analysis and used a targeted metabolomics approach to study de novo organ formation in tomato hypocotyl explants and found tissue-specific metabolic differences and divergent developmental pathways. Our results indicate that successful regeneration in the apical region of the hypocotyl depends on a specific metabolic switch involving the upregulation of photorespiratory pathway components and the differential regulation of photosynthesis-related gene expression and gluconeogenesis pathway activation. These findings provide a useful resource for further investigation of the molecular mechanisms involved in wound-induced organ formation in crop species such as tomato. [ABSTRACT FROM AUTHOR]

Salinity provokes an imbalance of vegetative to generative growth, thus impairing crop productivity. Unlike breeding strategies, grafting is a direct and quick alternative to improve salinity tolerance in horticultural crops, through rebalancing plant development. Providing that hormones play a key role in plant growth and development and stress responses, we hypothesized that rootstock-mediated reallocation of vegetative growth and yield under salinity was associated with changes in the hormonal balance. To test this hypothesis, the hybrid pepper variety (Capsicum annuum L. "Gacela F1") was either non-grafted or grafted onto three commercial rootstocks (Creonte, Atlante, and Terrano) and plants were grown in a greenhouse under control (0 mM NaCl) and moderate salinity (35 mM NaCl) conditions. Differential vegetative growth versus fruit yield responses were induced by rootstock and salinity. Atlante strongly increased shoot and root fresh weight with respect to the non-grafted Gacela plants associated with improved photosynthetic rate and K+ homeostasis under salinity. The invigorating effect of Atlante can be explained by an efficient balance between cytokinins (CKs) and abscisic acid (ABA). Creonte improved fruit yield and maintained the reproductive to vegetative ratio under salinity as a consequence of its capacity to induce biomass reallocation and to avoid Na+ accumulation in the shoot. The physiological responses associated with yield stability in Creonte were mediated by the inverse regulation of CKs and the ethylene precursor 1-aminocyclopropane-1-carboxylic acid. Finally, Terrano limited the accumulation of gibberellins in the shoot thus reducing plant height. Despite scion compactness induced by Terrano, both vegetative and reproductive biomass were maintained under salinity through ABA-mediated control of water relations and K+ homeostasis. Our data demonstrate that the contrasting developmental and physiological responses induced by the rootstock genotype in salinized pepper plants were critically mediated by hormones. This will be particularly important for rootstock breeding programs to improve salinity tolerance by focusing on hormonal traits. [ABSTRACT FROM AUTHOR]

Developing drought-tolerant crops is an important strategy to mitigate climate change impacts. Modulating root system function provides opportunities to improve crop yield under biotic and abiotic stresses. With this aim, a commercial hybrid tomato variety was grafted on a genotyped population of 123 recombinant inbred lines (RILs) derived from Solanum pimpinellifolium, and compared with self- and non-grafted controls, under contrasting watering treatments (100% vs. 70% of crop evapotranspiration). Drought tolerance was genetically analyzed for vegetative and flowering traits, and root xylem sap phytohormone and nutrient composition. Under water deficit, around 25% of RILs conferred larger total shoot dry weight than controls. Reproductive and vegetative traits under water deficit were highly and positively correlated to the shoot water content. This association was genetically supported by linkage of quantitative trait loci (QTL) controlling these traits within four genomic regions. From a total of 83 significant QTLs, most were irrigation-regime specific. The gene contents of 8 out of 12 genomic regions containing 46 QTLs were found significantly enriched at certain GO terms and some candidate genes from diverse gene families were identified. Thus, grafting commercial varieties onto selected rootstocks derived from S. pimpinellifolium provides a viable strategy to enhance drought tolerance in tomato. [ABSTRACT FROM AUTHOR]

• Constitutive ABA overproduction reduces shoot and root growth and close stomata, under optimal conditions. • Constitutive ABA overproduction reduces the percentage loss in shoot and root growth, under salinity conditions. • Constitutive ABA overproduction increases the total root length, under salinity conditions. • Constitutive ABA overproduction limited plant growth under optimal conditions by altering growth regulatory gene networks. • Salinity differentially altered the growth regulatory gene networks in ABA overproducing plants, thereby sustaining growth. To better understand abscisic acid (ABA)'s role in the salinity response of tomato (Solanum lycopersicum L.), two independent transgenic lines, sp5 and sp12, constitutively overexpressing the LeNCED1 gene (encoding 9- cis -epoxycarotenoid dioxygenase, a key enzyme in ABA biosynthesis) and the wild type (WT) cv. Ailsa Craig, were cultivated hydroponically with or without the addition of 100 mM NaCl. Independent of salinity, LeNCED1 overexpression (OE) increased ABA concentration in leaves and xylem sap, and salinity interacted with the LeNCED1 transgene to enhance ABA accumulation in xylem sap and roots. Under control conditions, LeNCED1 OE limited root and shoot biomass accumulation, which was correlated with decreased leaf gas exchange. In salinized plants, LeNCED1 OE reduced the percentage loss in shoot and root biomass accumulation, leading to a greater total root length than WT. Root qPCR analysis of the sp12 line under control conditions revealed upregulated genes related to ABA, jasmonic acid and ethylene synthesis and signalling, gibberellin and auxin homeostasis and osmoregulation processes. Under salinity, LeNCED1 OE prevented the induction of genes involved in ABA metabolism and GA and auxin deactivation that occurred in WT, but the induction of ABA signalling and stress-adaptive genes was maintained. Thus, complex changes in phytohormone and stress-related gene expression are associated with constitutive upregulation of a single ABA biosynthesis gene, alleviating salinity-dependent growth limitation. [ABSTRACT FROM AUTHOR]

Abstract Fenugreek is a legume cultivated for its medicinal value, especially in arid and semi-arid regions, where soil salinity is an increasing problem. In fact, salinity is one of the major environmental factors limiting plant growth and productivity. Plant hormones are known to play vital roles in the ability of the plants to acclimatize to varying environments by mediating growth, development, and nutrient allocation. Thus, to gain insights about the role of plant hormones in the growth responses of salinized fenugreek plants (Trigonella foenum-graecum L.), a medium-term experiment was conducted under moderate (100 mM NaCl) and high (200 mM NaCl) salinity levels. Results showed that moderate, but especially high salinity stress, impaired shoot growth, total leaf area and leaf number. Salinity also provoked a reduction in relative water content, stomatal conductance and photosynthesis-related pigments, but, surprisingly, photosynthetic rate increased in the leaves of fenugreek plants. Na accumulated in the leaves, particularly at high salinity levels, while most mineral nutrients decreased. Furthermore, important changes in the main hormone classes were observed, associated to growth reduction under salinity. The active cytokinin form, trans -zeatin, and active cytokinin and gibberellin concentrations decreased with salinity in the leaves of fenugreek plants, whereas the ethylene precursor, 1-aminocyclopropane-1-carboxylic acid, accumulated in the roots of fenugreek plants, especially at high salinity levels. Importantly, leaf abscisic acid concentrations increased under salinity, which could limit leaf transpiration to adapt growth to the stressful conditions. Therefore, plant hormones seem to play a critical role in the growth responses of fenugreek plants under salinity stress and they could have potential interest in salt tolerance programmes for this species. [ABSTRACT FROM AUTHOR]

Summary: The effect of salt stress on nitrogen fixation, in relation to sucrose transport towards nodules and other sink organs and the potential of sucrose breakdown by nodules, was investigated in two lines of Medicago ciliaris. Under salt stress conditions, the two lines showed a decrease of total biomass production, but TNC 1.8 was less affected by salt than TNC 11.9. The chlorophyll content was not changed in TNC 1.8, in contrast to TNC 11.9. Shoot, root, and nodule biomass were also affected in the two lines, but TNC 1.8 exhibited the higher potentialities of biomass production of these organs. Nitrogen fixation also decreased in the two lines, and was more sensitive to salt than growth parameters. TNC 1.8 consistently exhibited the higher values of nitrogen fixation. Unlike nodules, leaves of both lines were well supplied in nutrients with some exceptions. Specifically, the calcium content decreased in the sensitive line leaves, and the nodule magnesium content was not changed in either line. The tolerant line accumulated more sodium in its leaves. The two lines did not show any differences in the nodule sodium content. Sucrose allocation towards nodules was affected by salt in the two lines, but this constraint did not seem to affect the repartition of sucrose between sink organs. Salt stress induced perturbations in nodule sucrolytic activities in the two lines. It inhibited sucrose synthase, but the inhibition was more marked in TNC 11.9; alkaline/neutral activity was not altered in TNC 1.8, whereas it decreased more than half in TNC 11.9. Thus, the relative tolerance of TNC 1.8 to salt stress could be attributed to a better use of these photoassimilates by nodules and a better supply of bacteroids in malate. The hypothesis of a competition for sucrose between nodules and other sink organs under salt stress could not be verified. [Copyright &y& Elsevier]

In order to reduce the negative effect of salinity on fruit yield, 5-day-old tomato seedlings (Lycopersicon esculentum) were haloconditioned by complete immersion in osmotic/saline solutions composed of PEG (−0. 5, −0. 75, −1MPa), with or without 10mM NaCl, for 1, 3, 5 and 8 days. Under moderate salinity (7. 5dSm−1), the pre-adapted plants produced 23% more shoot biomass and fruit yield than the non-adapted plants. In addition to the induced vigour, the improved tolerance in most pre-treatments was related to lower Na+ and Cl− concentrations in the leaves and increases in leaf K+ contents and K+/Na+ ratio, but the contrary was also observed. Overall, the most effective haloconditioning treatment seems to be the application of −0. 75MPa for 3 days. During the experiment in greenhouse, some vigorous haloconditioned plants were propagated through adventitious apex culture and evaluated under salinity in a short-term experiment. The results suggested that the induced salt tolerance was not horizontally transmitted, indicating that (i) the individuals chosen were not genetically more vigorous, but (ii) it is likely that they responded better to the induced adaptation, and (iii) this adaptation is probably mediated by epigenetic changes taking place in the roots. [Copyright &y& Elsevier]

In the present study, we exposed Medicago ciliaris isolated from a saline sebhka and growing symbiotically with Sinorhizobium medicae to 100 mM of NaCl and followed this stress by a recovery period (complete NaCl withdrawal from the root medium for two or one weeks). This experiment was conducted in order i) to check whether a reduction in growth and nitrogen fixation could be reversed by alleviating salt stress and ii) to determine specific changes related to salt-induced growth and nitrogen fixation decline. Salt stress reduced growth of all organs (particularly nodules), leaf area, photosynthetic activity and nitrogen fixation. The depressive effect of salt was not linked to osmotic stress. The removal of saline conditions restored growth of all organs after 2 weeks of recovery, with aerial organs recovering quickly after 1 week. Both photosynthetic and nitrogen fixation recovered only after a 2 week period of recovery. Salt stress in these saline-tolerant plants was accompanied by oxidative damage (electrolyte leakage), which was more accentuated in nodules in comparison with leaves. The observed recovery in growth, nitrogen fixation and photosynthesis was mainly linked to a preferential preservation of shoots growth owing to the maintenance of SOD activity (namely the isoforms A2 and A3); such maintenance would allow higher photosynthetic activity permitting an adequate supply of nodules with photoassimilates and thus facilitating stress withstand. [ABSTRACT FROM AUTHOR]

At a world scale, tomato is an important horticultural crop, but its productivity is highly reduced by drought stress. Combining the application of beneficial microbial inoculants with breeding and grafting techniques may be key to cope with reduced tomato yield under drought. This study aimed to investigate the growth responses and physiological mechanisms involved in the performance under drought stress of four tomato recombinant inbred lines (RIL) after inoculation with the arbuscular mycorrhizal (AM) fungus Rhizophagus irregularis and the plant growth promoting rhizobacteria (PGPR) Variovorax paradoxus 5C-2. Results showed a variation in the efficiency of the different tomato RILs under drought stress and a differential effect of the microbial inoculants, depending on the RIL involved. The inoculants affected plant parameters such as net photosynthetic capacity, oxidative damage to lipids, osmolyte accumulation, root hydraulic conductivity or aquaporin abundance and phosphorylation status. RIL66 was the one obtaining maximum benefit from the microbial inoculants under drought stress conditions, due likely to improved CO 2 -fixation capacity and root hydraulic conductivity. We propose that RIL66 could be selected as a good plant material to be used as rootstock to improve tomato growth and productivity under water limiting conditions. Since RIL66 is highly responsive to microbial inoculants, this grafting strategy should be combined with inoculation of R. irregularis and V. paradoxus in order to improve plant yield under conditions of drought stress. [ABSTRACT FROM AUTHOR]

Water availability is the most important factor limiting food production, thus developing new scientific strategies to allow crops to more efficiently use water could be crucial in a world with a growing population. Tomato is a highly water consuming crop and improving its water use efficiency (WUE) implies positive economic and environmental effects. This work aimed to study and exploit root-derived hormonal traits to improve WUE in tomato by grafting on selected rootstocks. Firstly, root-related hormonal parameters associated to WUE were identified in a population of recombinant inbred lines (RILs) derived from the wild tomato species Solanum pimpinellifolium . A principal component analysis (PCA) revealed that some hormonal traits were associated with productivity (plant biomass and photosynthesis) and WUE in the RIL population. Leaf ABA concentration was associated to the first component (PC1) of the PCA, which explained a 60% of the variance in WUE, while the ethylene precursor ACC and the ratio ACC/ABA were also associated to PC1 but in the opposite direction. Secondly, we selected RILs according to their extreme biomass (high, B, low, b) and water use (high, W, low, w), and studied the differential effect of shoot and root on WUE by reciprocal grafting. In absence of any imposed stress, there were no rootstock effects on vegetative shoot growth and water relations. Finally, we exploited the previously identified root-related hormonal traits by grafting a commercial tomato variety onto the selected RILs to improve WUE. Interestingly, rootstocks that induced low biomass and water use, ‘bw’, improved fruit yield and WUE (defined as fruit yield/water use) by up to 40% compared to self-grafted plants. Although other hormonal factors appear implicated in this response, xylem ACC concentration seems an important root-derived trait that inhibits leaf growth but does not limit fruit yield. Thus tomato WUE can be improved exploiting rootstock-derived hormonal signals which control leaf growth. [ABSTRACT FROM AUTHOR]

Abstract: Hormonal changes in two Medicago ciliaris lines differing in salt tolerance (TNC 1.8 being more tolerant than TNC 11.9) were studied as possible regulators of growth and symbiotic nitrogen fixation (SNF). After 21 days of saline treatment (100mM NaCl), four major phytohormones (abscisic acid, ABA; the cytokinin trans-zeatin, t-Z; the auxin indole-3-acetic acid, IAA; and the ethylene precursor 1-aminocyclopropane-1-carboxylic acid, ACC) were analysed. Salinity differently affected hormone concentrations in vegetative tissues and nodules in both lines. Principal component analysis (PCA) revealed that growth and SNF parameters under salinity were inversely correlated to the amount of reduced nitrogen (Nred) allocated to the roots and nodules, to the sucrolytic activity (TSA) in the roots, and to the t-Z and ABA concentration in the nodules. However, those parameters were positively associated along PC1 to the Nred and TSA in the leaves and all the hormones analysed in the roots. Interestingly, the ACC concentration of all organs was positively associated with vegetative growth and with SNF under salinity, as a putative regulator of the symbiotic-parasitic relation with the bacteria. The influence of hormonal changes in relation to plant growth, SNF and symbiotic relation is discussed. [Copyright &y& Elsevier]