Changes in ethylene evolution and polyamine profiles of seedlings of nine cultivars of Lactuca sativa L. in response to salt stress during germination

Lettuce seeds from nine cultivars were germinated under control and saline (150 mM NaCl) conditions. The effect of salt stress on germination, growth, ethylene production, respiration rate and polyamine levels was investigated. Salinity delayed germination and reduced the growth of all studied cultivars, but only significantly reduced final germination percentage in Inverna and Baby Star cultivars, while the other seven cultivars reached 100% germination under saline conditions. Respiration rate and ethylene production increased with salinity in all the nine lettuce cultivars. Moreover, cultivars that had a higher increase in ethylene production under salt stress showed the lowest reduction in fresh weight. The presence of salt reduced putrescine (Put) level, while spermidine (Spd) and spermine (Spin) increased. The effects of salinity on ethylene production and polyamine metabolism are discussed in relation to salinity tolerance of lettuce seedlings. The possible role of ethylene and polyamines as physiological markers for salinity tolerance in lettuce seedlings is also discussed. (C) 2003 Elsevier Science Ireland Ltd. All rights reserved.