Physiological mechanism of tolerance of Lycopersicon spp. exposed to salt stress

Abstract

The physiological mechanism of salt tolerance in Lycopersicon spp. was investigated. Ten Lycopersicon spp. were exposed to a gradual NaCl-induced decline in root zone water potential of −0.10 MPa d−1 for 10 d and maintained at −1.065 MPa (221.4 mM NaCl) for a period of 20 d. Growth, water relations and accumulation of ions and compatible solutes, such as proline and the quaternary ammonium compound, trigonelline (methylated nicotinic acid), were studied and correlated. Salt tolerance, measured as growth, in selected Lycopersicon species of varying ecological habitats indicated that L. cheesmanii, native to a saline-coastal habitat, was the most tolerant and L. pennellii, the most sensitive. The commercial cultivar, L. esculentum 'Duke', ranked 7th in the order of relative tolerance to salt. All species accumulated proline in all organs in response to salinity; but there was no general relationship between the ability of these species to accumulate proline and their relative salt tolerance. Relative trigonelline accumulation in meristematic tissues of NaCl-stressed plants correlated with the salt tolerance of these species, however, as did their ability to (1) maintain turgor in the expanding leaves, (2) exclude Na+ from the expanded leaves and (3) exclude Cl− from the root tissues. Key words: Chloride accumulation index, Lycopersicon spp., proline accumulation index, salt tolerance index, sodium accumulation index, trigonelline accumulation index, water potential