Improving crop salt tolerance using transgenic approaches: An update and physiological analysis

Salinization of land is likely to increase due to climate change with impact on agricultural production. Since most species used as crops are sensitive to salinity, improvement of salt tolerance is needed to maintain global food production. This review summarises successes and failures of transgenic approaches in improving salt tolerance in crop species. A conceptual model of coordinated physiological mechanisms in roots and shoots required for salt tolerance is presented. Transgenic plants overexpressing genes of key proteins contributing to Na⁺ ‘exclusion’ (PM-ATPases with SOS1 antiporter, and HKT1 transporter) and Na⁺ compartmentation in vacuoles (V-H⁺ATPase and V-H⁺PPase with NHX antiporter), as well as two proteins potentially involved in alleviating water deficit during salt stress (aquaporins and dehydrins), were evaluated. Of the 51 transformations, with gene(s) involved in Na⁺ ‘exclusion’ or Na⁺ vacuolar compartmentation that contained quantitative data on growth and include a non-saline control, 48 showed improvements in salt tolerance (less impact on plant mass) of transgenic plants, but with only two tested in field conditions. Of these 51 transformations, 26 involved crop species. Tissue ion concentrations were altered, but not always in the same way. Although glasshouse data are promising, field studies are required to assess crop salinity tolerance.     

Mast cell histamine release induced by Portuguese man-of-war (Physalia) venom

Nematocyst venom from Portuguese Man-of War ($\text{Physalia}$ sp.) tentacles causes isolated rat peritoneal mast cells to release histamine. Extent of histamine release is dose-dependent (K_0.5 = 6.1 μg venom/ml) and attains 100% at high doses of venom. Release is independent of intra- and extracellular calcium levels and does not depend upon a cellular supply of ATP. The rate of histamine release is temperature-dependent and the extent of release is maximized broadly over the range of 10–30°C. The cytoplasmic marker lactate dehydrogenase, is released concomitantly with histamine but is more sensitive to the venom (K_0.5 = 2.1 μg/ml). Antimycin A, while it does not significantly affect venom-induced histamine release, increases the sensitivity of lactate dehydrogenase release (K_0.5 = 0.2 μg/ml). We conclude that $\text{Physalia}$ nematocyst venom induces the release of histamine from mast cells by a cytolytic mechanism and that this action is antagonized by an intracellular, energy-requiring process.     

ABCA1 is essential for efficient basolateral cholesterol efflux during the absorption of dietary cholesterol in chickens

The ATP-binding cassette transporter A1 (ABCA1) participates in the efflux of cholesterol from cells. It remains unclear whether ABCA1 functions to efflux cholesterol across the basolateral or apical membrane of the intestine. We used a chicken model of ABCA1 dysfunction, the Wisconsin hypoalpha mutant (WHAM) chicken, to address this issue. After an oral gavage of radioactive cholesterol, the percentage appearing in the bloodstream was reduced by 79% in the WHAM chicken along with a 97% reduction in the amount of tracer in high density lipoprotein. In contrast, the percentage of radioactive cholesterol absorbed from the lumen into the intestine was not affected by the ABCA1 mutation. Liver X receptor (LXR) agonists have been inferred to decrease cholesterol absorption through activation of ABCA1 expression. However, the LXR agonist T0901317 decreased cholesterol absorption equally in both wild type and WHAM chickens, indicating that the effect of LXR activation on cholesterol absorption is independent of ABCA1. The ABCA1 mutation resulted in accumulation of radioactive cholesterol ester in the intestine and the liver of the WHAM chicken (5.0- and 4.4-fold, respectively), whereas biliary lipid concentrations were unaltered by the WHAM mutation. In summary, ABCA1 regulates the efflux of cholesterol from the basolateral but not apical membrane in the intestine and the liver.     

OPTIMIZATION OF CULTURE CONDITIONS FOR ENUMERATION OF H2S BACTERIA IN THE FLESH OF SEAFISH

H₂S bacteria of seafish flesh are weakly halophilic and require on average 1.68% NaCl according to statistical studies. Enumeration is optimal on PCA-H₂S(a PCA medium supplemented with sulfur sources and increased NaCl concentrations) incubated at 25C. Total aerobic bacteria can be counted simultaneously on this medium. The proportion of H₂S bacteria relative to total aerobic bacteria increased slightly during prolonged storage of the fish, but was highly variable. Models relating H₂S bacterial counts to spoilage of fish are sigmoidal and showed that when the count exceeds 10,000 CFU/g, whole or filleted fish stored in ice at 0C are unfit for consumption. Shewanella putrefaciens accounted for 69% of the H₂S bacteria at the fifth day of storage and 100% at the fifteenth.     

Enhanced reactivation and enhanced mutagenesis of herpes simplex virus in normal human and xeroderma pigmentosum cells.

Enhanced reactivation (ER) and enhanced mutagenesis (EM) of herpes simplex virus type 1 were studied simultaneously in UV-irradiated stationary cultures of diploid normal human and xeroderma pigmentosum (XP) fibroblasts. Mutagenesis was assayed with unirradiated herpes simplex virus type 1 as a probe in a forward mutation assay (resistance to iododeoxycytidine). Dose-response studies showed that ER increased with the UV dose given to the virus. Optimal reactivation levels were obtained when normal cells and XP variant cells were exposed to a UV dose of 8 J . m-2 and the virus was irradiated with 150 J . m-2. Repair-deficient XP cells of complementation groups A, C, and D showed optimal reactivation levels with a UV dose to the cells of 1.0 J . m-2 and a UV dose to the virus of 40 J . m-2. The time course of appearance of ER and EM was also studied, both in the normal and XP cells. In all cell types except the XP variant cells, EM followed similar kinetics of appearance as did ER. Maximal activities occurred when infection was delayed 1 or 2 days after cell treatment. In XP variant cells, however, maximal expression of the EM function was significantly delayed with respect to ER. The results indicate that ER and EM are transiently expressed in normal and repair-deficient XP cells. Although both phenomena may be triggered by the same cellular event, ER and EM appear to be separate processes that occur independently of each other.     

Effects of triclosan on growth, viability and fatty acid synthesis of the oyster protozoan parasite Perkinsus marinus

Perkinsus marinus, a protozoan parasite of the Eastern oyster Crassostrea virginica, has severely impacted oyster populations from the Mid-Atlantic region to the Gulf of Mexico coast of North America for more than 30 yr. Although a chemotherapeutic treatment to reduce or eliminate P. marinus from infected oysters would be useful for research and hatchery operations, an effective and practical drug treatment does not currently exist. In this study, the antimicrobial drug triclosan 5-chloro-2-(2,4 dichlorophenoxy) phenol, a specific inhibitor of Fab1 (enoyl-acyl-carrier-protein reductase), an enzyme in the Type II class of fatty acid synthetases, was tested for its effects on viability, proliferation and fatty acid synthesis of in vitro-cultured P. marinus meronts. Treatment of P. marinus meront cell cultures with concentrations of > or = 2 microM triclosan at 28 degrees C (a temperature favorable for parasite proliferation) for up to 6 d stopped proliferation of the parasite. Treatment at > or = 5 microM at 28 degrees C greatly reduced the viability and fatty acid synthesis of meront cells. Oyster hemocytes treated with > or = 20 microM triclosan exhibited no significant (p < 0.05) reduction in viability relative to controls for up to 24 h at 13 degrees C. P. marinus meronts exposed to > or = 2 microM triclosan for 24 h at 13 degrees C exhibited significantly (p < 0.05) lower viability relative to controls. Exposure of P. marinus meronts to triclosan concentrations of > or = 20 microM resulted in > 50% mortality of P. marinus cells after 24 h. These results suggest that triclosan may be effective in treating P. marinus-infected oysters.     

Annual breeding in a captive smalltooth sawfish,Pristis pectinata

The critically endangered smalltooth sawfish Pristis pectinata reproduces biennially in central west Florida, U.S.A. Here we demonstrate that smalltooth sawfish are physiologically capable of reproducing annually in a captive environment. The smalltooth sawfish are held in an open system, with abiotic conditions that vary naturally with the surrounding environment in The Bahamas. This suggests wild smalltooth sawfish may also be capable of annual reproduction provided there are adequate prey resources, limited competition and mate availability.