Sodium nitroprusside, ferricyanide, nitrite and nitrate decrease the thermo-dormancy of lettuce seed germination in a nitric oxide-dependent manner in light

Abstract

Lettuce (L. sativa L. ‘Jianye Xianfeng No. 1’) seeds can exhibit both photodormancy and thermodormancy (thermoinhibition); however, the mechanism for thermoinhibition of seed germination is poorly understood. Here, we have investigated the response of lettuce seed germination to temperature and light, the effect of sodium nitroprusside (SNP), potassium ferricyanide (Fe(III)CN), nitrite, nitrate and NO scavenger 2-phenyl-4,4,5,5-tetramethylimidazoline-1-oxyl 3-oxide (PTIO) on the thermoinhibition of seed germination, and the inhibiting role of PTIO on SNP, Fe(III)CN, and acidified nitrite to determine the mechanisms of thermoinhibition of seed germination. Our data showed that the optimal temperature for Jianye Xianfeng No. 1 lettuce seed germination was 13–15 °C in darkness, and 11–19 °C in light. The thermoinhibition of seed germination could be decreased by SNP, Fe(III)CN, nitrite and nitrate in light and by nitrite and nitrate in darkness. Changes in lettuce seed germination caused by PTIO at 1–200 μM were not observed at the optimal temperatures. Germination was increased by PTIO at 1–100 μM and was decreased by PTIO at 200 μM in light at 23 °C, and that was gradually decreased by 1–200 μM in darkness at 17 °C. In light, SNP, Fe(III)CN and vapours produced by SNP, Fe(III)CN and acidified nitrite could effectively decrease the thermoinhibition of seed germination, and these promoting effects were inhibited by PTIO at 200 μM. In darkness, nitrate and nitrite at 5 and 10 mM plus PTIO stimulated the germination of seeds. Our data show that thermoinhibition of lettuce seed germination is temperature- and light-dependent, was decreased by SNP, Fe(III)CN, nitrite and nitrate in a nitric oxide-dependent manner in light.