Ethanol, at physiological concentrations, affects ethylene sensing in tomato germinating seeds and seedlings

Ethanol is known to accumulate in various plant organs under various environmental conditions. However, there are very scarce data about ethanol sensing by plants. We observed that ethanol accumulates up to 3.5 mM during tomato seed imbibition, particularly when seeds were stacked. Stacked seeds germinated less than spread out seeds suggesting ethanol inhibits germination. In support of this, exogenous ethanol at physiological concentrations, ranging from 1 to 10 mM, inhibited germination of wild type tomato seeds. However, the germination pattern over the whole ethanol concentration range tested was modified in an ethylene insensitive mutant, never-ripe (nr). The effects of exogenous ethanol were not linked to differences in ethylene production by imbibed seeds. But, we observed that exogenous ethanol at a concentration as low as 0.01 mM down regulated the expression of some ethylene receptors. Moreover, the triple response induced by ethylene in tomato seedlings was partially alleviated by 1 mM ethanol. Similar observations were made on Arabidopsis seeds. These results show there are interactions between ethylene sensing and ethanol in plants.