Overexpression of the HAL1 gene in yeast has a positive effect on salt tolerance by maintaining a high internal K ϩ concentration and decreasing intracellular Na ϩ during salt stress. In the present work, the yeast gene HAL1 was introduced into tomato (Lycopersicon esculentum Mill.) by Agrobacterium tumefaciens-mediated transformation. A sample of primary transformants was self-pollinated, and progeny from both transformed and non-transformed plants (controls) were evaluated for salt tolerance in vitro and in vivo. Results from different tests indicated a higher level of salt tolerance in the progeny of two different transgenic plants bearing four copies or one copy of the HAL1 gene. In addition, measurement of the intracellular K ϩ to Na ϩ ratios showed that transgenic lines were able to retain more K ϩ than the control under salt stress. Although plants and yeast cannot be compared in an absolute sense, these results indicate that the mechanism controlling the positive effect of the HAL1 gene on salt tolerance may be similar in transgenic plants and yeast.

The responses of five tomato cultivars (L. esculentum Mill) of different degrees of salt tolerance were examined over a range of 0 to 140 mM NaC1 applied for 3 and 10 weeks. Judged by both Na and C1 accumulations and maintenance of K, Ca and Mg contents with increasing salinity, the most tolerant cultivars (Pera and GC-72) showed different responses. The greater salt tolerance of cv Pera was associated with a higher C1 and Na accumulation and a lower K content in the shoot than those found in the other cultivars, typical of a halophytic response to salinity. However, the greater salt tolerance of cv GC-72 was associated with a retention of Na and CI in the root, restriction of their translocation to the shoot and maintenance of potassium selectivity under saline conditions. The salt tolerance mechanisms that operated in the remaining cultivars were similar to that of cv GC-72, as at first they excluded Na and C1 from the shoots, accumulating them in the roots; with longer treatment, the ability to regulate Na and C1 concentrations in the plant was lost only in the most salt sensitive cultivar (Volgogradskij), resulting in a massive influx of both ions into the shoot.The salt sensitivity of some tomato cultivars to salinity could be due to both the toxic effect of Na and C1 ions and nutritional imbalance induced by salinity, as plant growth was inversely correlated with Na and C1 contents and directly correlated with K and Ca contents. This study displays that there is not a single salt tolerance mechanism, since different physiological responses among tomato cultivars have been found.

The effects of seed priming with 6 M NaCl solution have been investigated with respect to growth and physiological responses of tomato plants (Lycopersicon esculentum Mill. cv. Pera) exposed to 70 and 140 mM NaCl nutrient solutions from 11 to 60 days after sowing. Tomato seedlings from primed seeds emerged earlier than from non‐primed seeds. At 70 mM, a lower shoot and root dry weight reduction was found in plants from primed seeds at the different harvests (30, 45 and 60 days after sowing), while at 140 mM the positive effect of seed priming was only shown in roots. Significant changes in Na+ and CI− accumulation with seed priming were only found in roots at 60 days after sowing, with ion accumulation in roots being higher in plants grown at 70 and 140 mM from primed seeds. In leaves of salt‐treated plants, significant increases in sugars and organic acids with seed priming were found from 30 days after sowing, and these increases were higher at longer treatment times. In roots, however, only the organic acids tended to increase in plants from primed seeds, although they increased less than in leaves, especially at 60 days after sowing. These results support the hypothesis that priming of seeds with NaCl induces physiological changes in the plants, changes which are shown more clearly at advanced growth stages.

The yeast HAL1 gene facilitates K + /Na + selectivity and salt tolerance of cells. Ectopic expression of HAL1 in transgenic tomato ( Lycopersicon esculentum Mill.) plants minimized the reduction in fruit production caused by salt stress. Maintenance of fruit production by transgenic plants was correlated with enhanced growth under salt stress of calli derived from the plants. The HAL1 transgene enhanced water and K + contents in both leaf calli and leaves in the presence of salt, which indicates that HAL1 functions in plants using a similar mechanism to that in yeast, namely by facilitating K + /Na + selectivity under salt stress.

The effects of increasing salinity on dry weight and ion concentration of shoots at various growth stages and on fruit yield in four tomato (Lycopersicon esculentum Mill.) genotypes were assessed. The salt treatments (35, 70, and 140 mm NaCl) were applied pre-emergence (seed sowing) (pre-E) and post-emergence (four-leaf stage) (post-E) and maintained during plant growth. Genotype salt tolerance, measured as shoot dry weight in response to increases in salt concentration, varied depending on plant growth stage and salt application time. When salt was applied pre-E, salt tolerance increased with plant age, whereas when applied post-E, 45-day-old plants were the most salt tolerant. Mature plants were similarly salt tolerant independent of the growth stage at which the salt treatments began. However, fruit yield of all genotypes was higher when salt was applied pre-E than post-E. Shoot dry weight decreased as shoot Cl and Na ion concentrations increased. During early growth stages, pre-E salt-treated plants had the highest Cl-and Na+ concentrations and the lowest shoot dry weights. However, at the advanced stages, shoot Cl- and Na Concentrations were equal for both salt application times. These results show that the plants must adapt to salinity during a period that allows them to develop a mechanism to regulate internal Cl- and Na+ concentrations and, thus, grow under high salinity.

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