Salt-induced Damage Research Articles

Using excised leaves to screen lucerne for salt tolerance

Salinity affects many physiological processes at all levels of plant structural organization. Being a physiologically and genetically complex trait, salinity tolerance implies a coordinated contribution of multiple mechanisms, making plant screening for salt tolerance extremely difficult. In this work, we show how the use of excised leaves can fulfill that task. We argue that, by adding NaCl directly to the transpiration stream, the protective effects of several mechanisms regulating Na+ delivery to the shoot are eliminated, enhancing PSII exposure to salinity treatment and resulting in a significant decline in leaf photochemistry (Fv/Fm characteristics). We suggest that measuring Fv/Fm characteristics on excised salt-treated leaves provides an opportunity to evaluate the efficiency of vacuolar Na+ compartmentation, arguably the most important feature for salt tolerance. We also explain the observed decline in Fv/Fm values as salt-induced structural damage to chloroplasts caused by oxidative stress.

Sucrose-Induced Tolerance to and Recovery from Deicing Salt Damage in Containerized Ilex aquifolium L. and Quercus robur L.

Two outdoor experiments were conducted using containerized trees of the species holly (Ilex aquifolium L.) and English oak (Quercus robur L.) to determine the effectiveness and feasibility of sucrose to improve tolerance to and recovery from deicing salt (sodium chloride [NaCl]) damage. In experiment one, sucrose plus a water-only control was applied as a root drench to containerized stock. Seventy-two hours later, NaCl was applied to both tree species as a root drench. At day 15 after NaCl application, effects on leaf chlorophyll a and b, carotenoid (lutein, β-carotene, neoxanthin, α-carotene), xanthophyll (zeaxanthin, antheraxanthin, violaxanthin) concentration, leaf necrosis, and chlorophyll fluorescence (Fv/Fm) were measured. In experiment 2, NaCl was applied as a root drench. At day 14 after NaCl application, plants were root drenched with sucrose plus a water-only control and recovery rates monitored by recording leaf necrosis, leaf chlorophyll concentration, and chlorophyll fluorescence over the proceeding 8 weeks. At week 8 after sucrose application, effects on tree growth were recorded. Sucrose was found to confer to both tree species a useful degree to tolerance to NaCl and improve recovery from salt-induced damage with promotion of photoxidative antioxidant pigments (carotenoids, xanthophylls) and chlorophylls strongly indicated as significantly contributing to the induction of NaCl tolerance.

Influence of abscisic acid and other plant growth regulators on citrus defense mechanisms to salt stress

Citrus yield and growth are deeply affected by salinity. In the present work we have studied the effectiveness of differentplant growth regulators such as abscisic acid, jasmonic acid and 8’-methylene methyl abscissate in protectingcitrus from salt-induced damage. Plants of Salustiana cultivar grafted onto Carrizo citrange were used for this purpose.Plants were watered with 100 mM NaCl and leaf abscission, ethylene production, chloride accumulation and net photosyntheticrate were measured. Non-treated plants showed a dramatic drop in photosynthetic activity in response tosalinity, an increase in leaf ethylene production and a high abscission rate as a result of a massive leaf chloride accumulation.Plants treated with jasmonic acid or 8’-methylene methyl abscisate did not show any physiological changein response to salt stress. However, plants treated with abscisic acid showed a high reduction in the parameters considered.These results suggest that abscisic acid plays a role in modifying citrus physiological behaviour in responseto salinity and could be helpful in their acclimation to saline conditions

Unsaturated fatty acids in membrane lipids protect the photosynthetic machinery against salt-induced damage in Synechococcus.

In this study, the tolerance to salt stress of the photosynthetic machinery was examined in relation to the effects of the genetic enhancement of the unsaturation of fatty acids in membrane lipids in wild-type and desA+ cells of Synechococcus sp. PCC 7942. Wild-type cells synthesized saturated and mono-unsaturated fatty acids, whereas desA+ cells, which had been transformed with the desA gene for the Delta12 acyl-lipid desaturase of Synechocystis sp. PCC 6803, also synthesized di-unsaturated fatty acids. Incubation of wild-type and desA+ cells with 0.5 M NaCl resulted in the rapid loss of the activities of photosystem I, photosystem II, and the Na+/H+ antiport system both in light and in darkness. However, desA+ cells were more tolerant to salt stress and osmotic stress than the wild-type cells. The extent of the recovery of the various photosynthetic activities from the effects of 0.5 M NaCl was much greater in desA+ cells than in wild-type cells. The photosystem II activity of thylakoid membranes from desA+ cells was more resistant to 0.5 M NaCl than that of membranes from wild-type cells. These results demonstrated that the genetically engineered increase in unsaturation of fatty acids in membrane lipids significantly enhanced the tolerance of the photosynthetic machinery to salt stress. The enhanced tolerance was due both to the increased resistance of the photosynthetic machinery to the salt-induced damage and to the increased ability of desA+ cells to repair the photosynthetic and Na+/H+ antiport systems.

Increased susceptibility to deoxycorticosterone acetate-salt-induced hypertension in endothelin-B-receptor-deficient rats.

We evaluated the role of endothelin-B- (ET(B)) receptor-mediated action in the development and maintenance of deoxycorticosterone acetate (DOCA)-salt-induced hypertension, cardiovascular hypertrophy and renal damage, using the spotting lethal (sl) rat which carries a naturally occurring deletion in the ET(B)-receptor gene. Homozygous (sl/sl) rats exhibit abnormal development of the neural crest-derived epidermal melanocytes and the enteric nervous system (ENS), and do not live beyond 1 month because of intestinal aganglionosis and resulting intestinal obstruction. Therefore, the dopamine-beta-hydroxylase (D betaH) promoter was used to direct ET(B) transgene expression in sl/sl rats to support normal ENS development. D betaH-ET(B) sl/sl rats live into adulthood and are healthy, expressing ET(B)-receptor in adrenals and other adrenergic neurons. When homozygous (sl/sl) and wild-type (WT) (+/+) rats, all of which were transgenic, were treated with DOCA and salt for 4 weeks, the homozygous rats exhibited significantly earlier and higher increases in systolic blood pressure than WT rats. The daily oral administration of ABT-627, a selective ET(A)-receptor antagonist, almost completely suppressed the DOCA-salt-induced hypertension in both groups. Renal dysfunction and histological damage induced by DOCA-salt treatment were more severe in homozygous than in WT rats. Increased and marked vascular hypertrophy of the aorta was also observed in homozygous rats, compared with WT rats. Renal and vascular injuries induced by DOCA and salt were significantly improved by ABT-627 administration. We propose that ET(B)-receptor-mediated actions are protective factors in the pathogenesis of DOCA-salt-induced hypertension. ET(A)-mediated actions are at least partly responsible for the increased susceptibility to DOCA-salt-induced hypertension and related tissue injuries in ET(B)-receptor-deficient rats.

Gene Therapy for Hypertension

Somatic gene delivery approaches have received wide attention as a new technique for studying gene expression and as a potential therapeutic tool in treating both inherited and acquired diseases. Recent studies using nonviral and viral vectors have shown great promise for gene therapy in hypertensive diseases. Potential targets for prospective gene therapy in hypertension include vasopressor renin-angiotensin system components and a number of vasodilator polypeptides such as tissue kallikrein-kinin, atrial natriuretic peptide, adrenomedullin and nitric oxide synthase. Antisense inhibition with oligonucleotides or cDNAs encoding renin, angiotensinogen, angiotensin-converting enzyme and angiotensin receptors has been shown to cause a prolonged blood pressure reduction in spontaneously hypertensive rats. To evaluate the therapeutic potential of vasodilator proteins or peptides in high blood pressure, we delivered the genes encoding human tissue kallikrein, atrial natriuretic peptide, nitric oxide synthase, and adrenomedullin into hypertensive rat models and showed that a single injection resulted in a significant and sustained reduction of blood pressure for several weeks. The potency and duration of blood pressure reduction depends on the dose and the promoter of the gene administered, age and sex of the hypertensive animals as well as the vehicle used for gene delivery. Somatic gene transfer of human tissue kallikrein or atrial natriuretic peptide not only attenuated hypertension but also exerted a protective effect against salt-induced renal damage and cardiac hypertrophy in Dahl salt-sensitive rats after high salt loading. These results suggest that the application of antisense inhibition of vasopressors, or gene delivery of vasodepressors for gene therapy, may have potential in treating human hypertension, and cardiovascular and renal disorders.

Membrane cholesterol content of cholesterol/phospholipid vesicles determines the susceptibility to both damage and protection by bile salts: implications for bile physiology.

To investigate the effect of membrane lipid composition on the susceptibility to bile salt damage and protection. Artificial model cholesterol/phospholipid (c/p) membranes (vesicles) with a varying cholesterol (0-15 mM) and phospholipid content (3-30 mM), and with a c/p ratio ranging up to 1.70, were prepared by sonication. We examined the effect of incubation with increasing concentrations of either tauroursodeoxycholate (TUDC), taurocholate (TC) or taurodeoxycholate (TDC) alone, or with proportionally varying mixtures of TUDC and TDC. Vesicle integrity was assessed by the change in optical absorbance at 340 nm. Absorption of the bile salt-vesicle mixture decreased, with increasing bile salt concentration and hydrophobicity: TUDC less than TC less than TDC. Moreover, bile salt-induced damage also depended on membrane composition: vesicles containing more than 5 mM cholesterol and with a c/p ratio greater than 0.8 were less likely to be solubilized by 30 mM bile salt. Similarly, only in cholesterol-rich vesicles (c/p > 0.5) was a protective effect of TUDC against membrane disruption by TDC revealed upon incubation with various TUDC/TDC mixtures. Apart from the bile salt concentration and hydrophobicity, the cholesterol content of vesicles is pivotal, both in the bile salt-induced solubilization of cholesterol/phospholipid vesicles and in the potency of TUDC to prevent this.

Bile salt-induced increases in duodenal brush-border membrane proton permeability, fluidity, and fragility

Rabbit duodenal brush-border membrane vesicles were treated in vitro with deoxycholate, glycodeoxycholate, or taurodeoxycholate. Intravesicular [14C]glucose space at equilibrium, 0.54 microliters/mg protein, was reduced by exposure to the three bile salts in a concentration (0.1-5.0 mM)-dependent manner, equatable with increased membrane fragility. Net proton permeability (Pnet), determined by acridine orange fluorescence quenching, was increased from 6.3 x 10(-4) cm/sec in untreated vesicles, by approximately 120, 150, and 170%, by treatment with bile salts at 0.1, 0.5 and 1.0 mM, respectively. The three bile salts were equipotent. The increases in membrane fragility and Pnet were not accompanied by significant increases in membrane fluidity, as assessed from steady-state and time-resolved diphenylhexatriene fluorescence anisotropy. The data demonstrate direct effects of bile salts on duodenal apical membrane fragility and proton permeability that are likely to be early events in bile salt-induced mucosal damage.

Bond Strength of Epoxy-Coated Reinforcing Bars

Epoxy-coated bars are used in nearly all types of structures where corrosion may cause deterioration. Bridge decks and parking garages are especially susceptible to salt-induced damage. For satisfactory structural performance, bond between concrete and steel is essential, and the effect of coatings that might decrease bond should be considered in designs. In this study, 21 beams with lap splices in a constant moment region were tested in nine groups and the bond strength of epoxy-coated bars was compared to that of uncoated bars. Variables were bar size, concrete strength, casting position, and coating thickness. In each test group, the only variable was the coating thickness.

Salt-Induced Damage to Rice Plants and Alleviation Effect of Silicate

Rice plants were grown hydroponicaIly in the presence of either NaCI, sea water, or polyethylene glycol (PEG: average molecular weights of 7,800–9,000) at an osmotic potential of up to 186 mOsmol/kg, equivalent to 100 mM NaCI or 20% sea water, and the growth and mineral composition of the plants were compared. NaCI was the most detrimental agent, followed by sea water and PEG. Mineral contents, including nitrogen, phosphorus, potassium, and calcium were not significantly affected by the treatments. Removal of silicate from the culture solution brought about a more severe growth reduction in rice plants subjected to 100 mM NaCI stress. In the plants which received silicate, the contents of sodium in the shoots were nearly half of those in the shoots of plants which did not receive silicate.

Parenterally administered salivary tissue extracts reduce outputs of Na+ and K+ associated with bile salt-induced damage of rat oxyntic mucosa.

Extirpation of the major salivary glands in rats has been shown to exacerbate the ionic fluxes associated with pharmacologically-induced damage to the gastric mucosal barrier. In the present study we have investigated the effect of the administration of a crude extract of submandibular-sublingual salivary glands on gastric secretion and gastric mucosal barrier integrity in the rat. The extract was administered in a dose (4 mg protein) which would reduce established acid secretion by 30%. Chronic parenteral (intraperitoneal) administration of salivary gland extract but not phosphate buffer resulted in a reduction in the luminal appearance of Na+ and K+ associated with bile salt-induced damage (5 mM sodium taurocholate in 150 mM HCl) to the gastric mucosa of sialoadenectomized animals. Oral administration of the extract depressed its protective action. Boiling the extract prior to parenteral administration also abolished its ability to protect the mucosa. Acute administration of the extract by intraperitoneal injection only 30 min prior to bile salt treatment was also ineffective. These results suggest that chronic parenteral but not enteral treatment with a crude salivary gland extract aids in the maintenance of the gastric mucosal barrier in sialoadenectomized rats. The inability of acute administration of the extract to reduce the net fluxes of Na+ and K+ suggests that its mode of action is not entirely dependent upon an inhibition of gastric acid secretion.

Influence of Desalivation on Acid Secretory Output and Gastric Mucosal Integrity in the Rat

Exogenous administration of substances extracted from rodent salivary glands may increase the resistance of gastric mucosal barrier to the disruptive actions of ulcerogenic agents and/or reduce acid secretory output. In the present study the influence of desalivation in the rat on acid secretory function and mucosal integrity has been investigated. Experiments were performed on rats 4 wk after removal of the major salivary glands and ligation of the salivary ducts. Intravenous infusion of pentagastrin (0.1--0.4 microgram/kg/min) resulted in an increase in acid output in desalivated rats although the responses was less than that observed in sham-operated controls. Intraluminal instillation of a bile salt solution (5 mM in 150 mM HCl) in control animals resulted in a significant loss of H+ and the luminal appearance of Na+ and K+. The net fluxes of Na+ and K+ were exacerbated in the desalivated group. Furthermore, the mean area of bile salt-induced ulceration was significantly greater in desalivated rats than in the control group. In the absence of bile salt treatment there was no difference in either the transmural ionic fluxes or area of ulceration between the two groups. These results suggests that removal of the major salivary glands in rats decreases the resistance of the gastric mucosa to bile salt-induced damage.

Studies of Salt-Induced Damage to Roadside Plants in Ontario

"Salt applied to highways runs off into streams increasing their salt content during the winter and penetrates the soil resulting in elevated levels of Na and Cl within 30 m of the highway. The salt that is most damaging to vegetation is that which is carried onto trees and shrubs as wind-borne spray: Evergreens are very sensitive, as can be seen when needles turn brown in early spring. Buds and twigs are killed on deciduous trees, flower buds being the more sensitive. Injury can be reduced by planting tolerant species in salt spray areas."

Selection of Trees for Tolerance to Salt Injury

No plants are wholly immune to salt injury and this should be considered before any type of breeding-screeningselection process is initiated. Salinity, like other stressful features of the environment, results in the evolution of races, or ecotypes adapted to it. The possibility of breeding salt tolerance into plants exists, but the strategy has not been tried in any sustained energetic manner. Salt usage, especially deicing, is increasing yearly. Plants growing along highways, on lawns, and along sidewalks exhibit stem dieback, and many are killed. The salts are deposited as spray on buds, stems, and leaves or are accumulated in the root zone. Subsequent injury results from osmotic and/or specific ion effects. Evaluations of salt-induced injury should be based on salts, concentrations, application methods, osmotic effects, shoot or leaf contents of Cl, and perhaps, shoot levels of Na. The appearance of the plant is not always reflective of the salt-induced damage, and growth parameters should be used to augment visual evaluations.