Exogenous CaCl₂ enhanced adventitious root formation in Cucumis sativus L. under cadmium stress through protein...

Cadmium (Cd) stress severely hinders plant growth and development. Calcium ion (Ca^2 +) and nitric oxide (NO) are involved in plant growth processes and stress responses. However, their crosstalk in adventitious rooting under Cd stress remains unclear. In this study, the effect of Ca²⁺ on enhancing the adventitious root development of cucumber under Cd condition was dose-dependent, with a maximal biological response at 200 μM CaCl₂. Moreover, Ca²⁺ chelator obviously reversed the positive influence of Ca²⁺ on promoting adventitious rooting under Cd stress, which indicates that Ca²⁺ is indispensable for the adventitious rooting under Cd stress. Meanwhile, removing endogenous NO significantly reversed Ca²⁺-induced root promotion under Cd stress. Furthermore, exogenous Ca²⁺ significantly increased endogenous NO production and total S-nitrosothiol (SNO) level under Cd stress implies that S-nitrosylation might be involved in Ca²⁺-induced adventitious root formation under Cd stress. To further investigate whether S-nitrosylation is key molecular switch of Ca²⁺-induced adventitious rooting under Cd stress, the potential S-nitrosylated proteins have been identified. An increase in the total S-nitrosylated proteins was detected under CaCl₂ treatment. Nevertheless, Ca²⁺ chelator significantly reduced the level of Ca²⁺-induced protein S-nitrosylation under Cd stress. A total of 117 S-nitrosylated proteins have been identified which mainly enriched in various biological processes, such as oxidation-reduction process, metabolic process, glycolytic process and so on. Additionally, denitrosylation agent treatment obviously decreased the activities of key enzymes during adventitious rooting under stress condition. These results suggest that Ca²⁺-induced S-nitrosylation of key proteins might participate in various pathways through differential S-nitrosylation during adventitious rooting under Cd stress. In summary, Ca²⁺ could promote the adventitious rooting under Cd stress by NO-dependent S-nitrosylation.