Hormonal changes in relation to biomass partitioning and shoot growth impairment in salinised tomato (Solanum lycopersicum L.) plants.

Following exposure to salinity, the root/shoot ratio is increased (an important adaptive response) due to the rapid inhibition of shoot growth (which limits plant productivity) while root growth is maintained. Both processes may be regulated by changes in plant hormone concentrations. Tomato plants (Solanum lycopersicum L. cv Moneymaker) were cultivated hydroponically for 3 weeks under high salinity (100 mM NaCl) and five major plant hormones (abscisic acid, ABA; the cytokinins zeatin, Z, and zeatin-riboside, ZR; the auxin indole-3-acetic acid, IAA; and the ethylene precursor 1-aminocyclopropane-1-carboxylic acid, ACC) were determined weekly in roots, xylem sap, and leaves. Salinity reduced shoot biomass by 50–60% and photosynthetic area by 20–25% both by decreasing leaf expansion and delaying leaf appearance, while root growth was less affected, thus increasing the root/shoot ratio. ABA and ACC concentrations strongly increased in roots, xylem sap, and leaves after 1 d (ABA) and 15 d (ACC) of salinization. By contrast, cytokinins and IAA were differentially affected in roots and shoots. Salinity dramatically decreased the Z+ZR content of the plant, and induced the conversion of ZR into Z, especially in the roots, which accounted for the relative increase of cytokinins in the roots compared to the leaf. IAA concentration was also strongly decreased in the leaves while it accumulated in the roots. Decreased cytokinin content and its transport from the root to the shoot were probably induced by the basipetal transport of auxin from the shoot to the root. The auxin/cytokinin ratio in the leaves and roots may explain both the salinity-induced decrease in shoot vigour (leaf growth and leaf number) and the shift in biomass allocation to the roots, in agreement with changes in the activity of the sink-related enzyme cell wall invertase

Involvement of source-sink relationship and hormonal control in the response of Medicago ciliaris — Sinorhizobium medicae symbiosis to salt stress

In order to explore the relationship between leaf hormonal status and source-sink relations in the response of symbiotic nitrogen fixation (SNF) to salt stress, three major phytohormones (cytokinins, abscisic acid and the ethylene precursor 1-aminocyclopropane-1-carboxylic acid), sucrose phosphate synthase activity in source leaves and sucrolytic activities in sink organs were analysed in two lines of Medicago ciliaris (salt-tolerant TNC 1.8 and salt-sensitive TNC 11.9). SNF (measured as nitrogenase activity and amount of N-fixed) was more affected by salt treatment in the TNC 11.9 than in TNC 1.8, and this could be explained by a decrease in nodule sucrolytic activities. SNF capacity was reflected in leaf biomass production and in the sink activity under salinity, as suggested by the higher salt-induced decrease in the young leaf sucrolytic activities in the sensitive line TNC 11.9, while they were not affected in the tolerant line TNC 1.8. As a consequence of maintaining sink activities in the actively growing organs, the key enzymatic activity for synthesis of sucrose (sucrose phosphate synthase) was also less affected in the mature leaves of the more tolerant genotype. Ours results showed also that the major hormone factor associated with the relative tolerance of TNC 1.8 was the stimulation of abscisic acid concentration in young leaves under salt treatment. This stimulation may control photosynthetic organ growth and also may contribute to a certain degree in the maintenance of coordinated sink-source relationships. Therefore, ABA may be an important component which conserves sucrose synthesis in source leaves

pH-Driven Polymorphic Behaviour of the Third PDZ Domain of PSD95: The Role of Electrostatic Interactions

The PDZ domains are modular domains that recognise short linear C-terminal sequences in proteins that organise the formation of complex multi-component assemblies. We have crystallised the third PDZ domain of the neuronal postsynaptic density-95 protein (PSD95-PDZ3) at mildly acidic pH conditions and obtained up to four polymorphs. Thus, below pH 4.0, the protein crystallised into prism-shaped crystals that belonged to the trigonal space group P3112. In contrast, above this pH value, the crystals’ shape changes to long needles belonging to the monoclinic P21 and two different orthorhombic packings of the P212121 space group. In addition, all the polymorphs share the main crystallographic interface, where the sidechain of the Asp332 imitates the binding of the C-terminal moiety to the canonical binding motif. Furthermore, we have analysed how changes in the ionisation state of some specific residues might be critical for crystallising the different polymorphs. The analysis of these polymorphs provides clues on the relevance of specific protein-protein interactions in protein crystallisation. However, these structures allow dissecting those electrostatic interactions that play a role in the conformation adopted by some residues and the extra-domain components upon binding C-terminal sequences

Genetic analysis of physiological components of salt tolerance conferred by Solanum rootstocks:what is the rootstock doing for the scion?

Grafting desirable crop varieties on stress-tolerant rootstocks provides an opportunity to increase crop salt tolerance. Here, a commercial hybrid tomato variety was grafted on two populations of recombinant inbred lines developed from a salt-sensitive genotype of Solanum lycopersicum var. cerasiforme, as female parent, and two salt-tolerant lines, as male parents, from S. pimpinellifolium, the P population, and S. cheesmaniae, the C population, to identify an easy screening method for identifying rootstocks conferring salt tolerance in terms of fruit yield. Potential physiological components of salt tolerance were assessed in the scion: leaf biomass, [Na+], nutrition, water relations and xylem ABA concentration. A significant correlation between scion fruit yield and scion leaf fresh weight, water potential or the ABA concentration was found in the C population under salinity, but the only detected QTL did not support this relationship. The rootstocks of the P population clearly affected seven traits related to the sodium, phosphorous and copper concentrations and water content of the scion leaf, showing heritability estimates around 0.4 or higher. According to heritability estimates in the P population, up to five QTLs were detected per trait. QTLs contributing over 15% to the total variance were found for P and Cu concentrations and water content of the scion leaf, and the proportion of fresh root weight. Correlation and QTL analysis suggests that rootstock-mediated improvement of fruit yield in the P population under salinity is mainly explained by the rootstock's ability to minimise perturbations in scion water status

Cholera control and anti-Haitian stigma in the Dominican Republic: from migration policy to lived experience

As cholera spread from Haiti to the Dominican Republic, Haitian migrants, a largely undocumented and stigmatized population in Dominican society, became a focus of public health concern. Concurrent to the epidemic, the Dominican legislature enacted new documentation requirements. This paper presents findings from an ethnographic study of anti-Haitian stigma in the Dominican Republic from June to August 2012. Eight focus group discussions (FGDs) were held with Haitian and Dominican community members. Five in-depth interviews were held with key informants in the migration policy sector. Theoretical frameworks of stigma's moral experience guided the analysis of how cholera was perceived, ways in which blame was assigned and felt and the relationship between documentation and healthcare access. In FGDs, both Haitians and Dominicans expressed fear of cholera and underscored the importance of public health messages to prevent the epidemic's spread. However, health messages also figured into experiences of stigma and rationales for blame. For Dominicans, failure to follow public health advice justified the blame of Haitians and seemed to confirm anti-Haitian sentiments. Haitians communicated a sense of powerlessness to follow public health messages given structural constraints like lack of safe water and sanitation, difficulty accessing healthcare and lack of documentation. In effect, by making documentation more difficult to obtain, the migration policy undermined cholera programs and contributed to ongoing processes of moral disqualification. Efforts to eliminate cholera from the island should consider how policy and stigma can undermine public health campaigns and further jeopardize the everyday ‘being-in-the-world’ of vulnerable groups