LAUSR

Main conclusion This report proves a cross talk between H 2 S and IAA in cold stress response, which has presented strong evidence that IAA acts as a downstream signal mediating the H 2 S-induced stress tolerance in cucumber seedlings. Abstract We evaluated changes in endogenous hydrogen sulfide (H 2 S) and indole-3-acetic acid (IAA) emission systems, and the interactive effect of exogenous H 2 S and IAA on chilling tolerance in cucumber seedlings. The results showed that chilling stress increased the activity and relative mRNA expression of l -/ d -cysteine desulfhydrase ( l -/ d -CD), which in turn induced the accumulation of endogenous H 2 S. Similarly, the endogenous IAA system was triggered by chilling stress. We found that 1.0 mM sodium hydrosulfide (NaHS, an H 2 S donor) significantly enhanced the activity of flavin monooxygenase (FMO) and relative expression of FMO-like proteins ( YUCCA2 ), which in turn elevated endogenous IAA levels in cucumber seedlings. However, IAA had little effects on activities of l -/ d -CD and endogenous H 2 S levels. H 2 S-induced IAA production accompanied by increase in chilling tolerance, as shown by the decrease in stress-induced electrolyte leakage (EL) and reactive oxygen species (ROS) accumulation, and increase in gene expressions and enzyme activities of photosynthesis. 1-naphthylphthalamic acid (NPA, an IAA polar transport inhibitor) declined H 2 S-induced chilling tolerance and defense genes’ expression. However, scavenging of H 2 S had a little effect on IAA-induced chilling tolerance. These results suggest that IAA acting as a downstream signaling molecule is involved in the H 2 S-induced chilling tolerance in cucumber seedlings.