The Involvement of Nitric Oxide and Ethylene on the Formation of Endodermal Barriers in Response of Cd In Sedum Alfredii

Nitric oxide (NO) and ethylene are both important signaling molecules which participate in numerous plant development processes and environmental stress resistance. Here, we investigate whether and how NO interacts with ethylene during the initiation of endodermal barriers that have major consequences for the apoplastic uptake of cadmium (Cd) in the hyperaccumulating ecotype of Sedum alfredii (HE). In response to Cd, an increased NO accumulation while a decrease in ethylene production was observed in the roots of HE. Exogenous supplementation, either NO donor (SNP) or NO scavenger (cPTIO), affected the ethylene production in roots. However, upon exogenous ethylene addition, roots retained their NO accumulation, suggesting that ethylene is downstream of the NO signaling pathway. Reduced contents of ACC and expressions of SaACS2, SaACS7 and SaACO2by exogenous SNP indicate that NO accumulation inhibited ethylene production via down-regulating expressions of ethylene synthesis genes. Correlation analysis indicates that NO positively modifies the formation of apoplastic barrier depending on the ethylene production, and the apoplastic barrier is major role for apoplast Cd uptake. Moreover, the interaction between NO and ethylene may decide the endodermal suberization via regulating SaGPAT5, SaASFT and SaCYP86A1, which is essential for Cd accumulation in shoots. Therefore, Cd-induced NO accumulation interferes with the synthesis of ethylene, leading to a deposition of endodermal barriers. However, in HE, a slight decrease of ethylene by nontoxic Cd only results in the increased proportion of partial-developed suberin lamellae. Interestingly, targeted metabolomics analysis prompts that it is worth further investigating NO-ABA interplay, which may accelerate the suberization