The responses of five tomato cultivars (L. esculentum Mill) of differe
nt degrees of salt tolerance were examined over a range of 0 to 140 mM
NaCl applied for 3 and 10 weeks. Judged by both Na and Cl accumulatio
ns and maintenance of K, Ca and Mg contents with increasing salinity,
the most tolerant cultivars (Pera and GC-72) showed different response
s. The greater salt tolerance of cv Pera was associated with a higher
Cl and Na accumulation and a lower K content in the shoot than those f
ound in the other cultivars, typical of a halophytic response to salin
ity. However, the greater salt tolerance of cv GC-72 was associated wi
th a retention of Na and Cl in the root, restriction of their transloc
ation to the shoot and maintenance of potassium selectivity under sali
ne conditions. The salt tolerance mechanisms that operated in the rema
ining cultivars were similar to that of cv GC-72, as at first they exc
luded Na and Cl from the shoots, accumulating them in the roots; with
longer treatment, the ability to regulate Na and Cl concentrations in
the plant was lost only in the most salt sensitive cultivar (Volgograd
skij), 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 Cl ions and nutritional imbalance indu
ced by salinity, as plant growth was inversely correlated with Na and
Cl contents and directly correlated with K and Ca contents. This study
displays that there is not a single salt tolerance mechanism, since d
ifferent physiological responses among tomato cultivars have