Search

• 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]

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]

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]