CsLCD and CsDCD are involved in nitric oxide-enhanced salt tolerance in cucumber seedlings.

Nitric oxide (NO) and hydrogen sulphide (HS) play important roles in plant growth, development and environmental adaptation. Currently, there is few information on the mechanism by which HS may be involved in NO-induced salt tolerance. In this study, cucumber was used to investigate the role of NO and HS and their relationship under salt stress. The results showed that the HS donor sodium hydrosulfide (NaHS) and the NO donor sodium nitroprusside (SNP) significantly promoted the growth of cucumber seedlings under salt stress. However, hypotaurine (HT, an HS scavenger) inhibited the positive effects of SNP under salt stress. Meanwhile, SNP treatment significantly increased the content of endogenous HS, the activity of HS synthesis-related enzymes LCD, DCD, and CAS, and the expression of HS synthesis-related genes (CsLCD and CsDCD). In addition, the salt tolerance of cucumber seedlings was largely eliminated after silencing the HS synthesis-related genes CsLCD/CsDCD, while overexpression of CsLCD/CsDCD significantly enhanced the salt tolerance. It was further found that SNP enhanced the salt tolerance of CsLCD/CsDCD overexpression lines, but it had no positive effect on the tolerance of CsLCD/CsDCD silencing lines. Therefore, NO might enhance salt tolerance in cucumber seedlings by upregulating the expression of HS synthesis-related gene CsLCD/CsDCD.