2017 ASHS Annual Conference

Diverse genotypes of lettuce were assessed for their seed germination responses to salt stress. The most tolerant genotype, PI251246, a primitive accession of Lactuca sativa, can germinate well at 250 mM NaCl, while the most sensitive genotypes are greatly inhibited at 225 mM NaCl. The inhibitory effect of salinity on germination was due to the osmotic stress rather than ionic toxicity. The inhibition of seed germination by salinity could be greatly alleviated by ethylene or partly by 1-aminocyclopropane carboxylic acid (ACC, ethylene precursor). Application of aminoethoxyvinylglycine (AVG, an ethylene biosynthetic inhibitor) and silver thiosulfate (STS, an ethylene receptor inhibitor) can completely block seed germination of PI251246 seeds at 250 and 200 mM NaCl, respectively. Ethylene production is seven times higher from PI251246 seeds than from UC96US23 seeds imbibed in 200 mM NaCl, although there is no significant difference between them when imbibed on water. Furthermore, free proline content of PI251246 seeds is significantly higher than that of UC96US23 seeds at 200 mM NaCl. Application of AVG or STS dramatically reduced free proline content of PI251246 seeds at 250 and 200 mM NaCl, respectively. Real-time PCR analysis showed that the transcript levels of ethylene biosynthetic gene LsACS1 and LsACO1 and of LsPDH1, a proline catabolic gene, are more abundant in PI251246 seeds imbibed in 200 mM NaCl than in other lettuce genotypes; STS greatly reduced their transcript levels in PI251246 seeds at 200 mM NaCl. However, seedling biomass and root length analyses revealed that the tolerance of PI251246 to salinity is specific to germination; seedling growth was not tolerant to salt stress. Thus, tolerance to osmotic stress during germination does not necessarily imply tolerance of seedling growth to salinity.