Salt tolerant tomato plants show increased levels of jasmonic acid

Tomato cultivars with different tolerance to NaCl were analysed for basal endogenous jasmonate (JAs) content, and its changes in response to salt-stress. Steady-state levels of JA and related compounds were higher in the "salt-tolerant cv. Pera than in cv. Hellfrucht Fruhstamm (HF) and JA levels in both cultivars changed in response to salt-stress. A steady JA increase was observed in cv. HF from the beginning of salinisation, while in cv. Pera, JA level decreased after 24 h of salt treatment. These results support the hypothesis that changes in endogenous JA in response to stress are different in genotypes of contrasting salt tolerance. The effects of salinity were then studied on lipoxygenase (LOX) protein accumulation, transcripts of allene oxide synthase (AOS) and proteinase inhibitor II (Pin2), and activities of diacylglycerol kinase (DAG-k) and phosphatidate kinase (PA-k) (enzymes involved in the phosphatidic acid (PA) and diacylglycerol pyrophosphate (DGPP) metabolism). The accumulation of a high molecular weight LOX-like protein was more pronounced in salt treated-plants of cv. HF, although both cultivars responded to exogenous JA treatment by increasing LOX accumulation. AOS-mRNA and Pin2-mRNA had also accumulated after 6 h of NaCl and JA treatments. An increase in the phosphorylation of phospholipids PA and DGPP was evident in cv. Pera, indicating that DAG-k and PA-k were highly activated by salt treatment only in this cultivar. Thus, the difference in the lipid kinase activities between both cultivars may be related to the process of salt stress tolerance rather than to JA synthesis.