Interaction between the signaling molecules hydrogen sulfide and hydrogen peroxide and their role in vacuolar H+‐ATPase regulation in cadmium‐stressed cucumber roots
2019
Kabała, Katarzyna | Zboińska, Magdalena | Głowiak, Dorota | Reda, Małgorzata | Jakubowska, Dagmara | Janicka, Małgorzata
Vacuolar H⁺‐ATPase (V‐ATPase; EC 3.6.3.14) is the main enzyme responsible for generating a proton gradient across the tonoplast. Under cadmium (Cd) stress conditions, V‐ATPase activity is inhibited. In the present work, hydrogen sulfide (H₂S) and hydrogen peroxide (H₂O₂) cross‐talk was analyzed in cucumber (Cucumis sativus L.) seedlings exposed to Cd to explain the role of both signaling molecules in the control of V‐ATPase. V‐ATPase activity and gene expression as well as H₂S and H₂O₂ content and endogenous production were determined in roots of plants treated with 100 μM CdCl₂ and different inhibitors or scavengers. It was found that H₂S donor improved photosynthetic parameters in Cd‐stressed cucumber seedlings. Cd‐induced stimulation of H₂S level was correlated with the increased activities of the H₂S‐generating desulfhydrases. Increased H₂O₂ and lowered H₂S contents in roots were able to reduce V‐ATPase activities similar to Cd. H₂O₂ and H₂S‐induced modulations in V‐ATPase activities were not closely related to the transcript level of encoding genes, suggesting posttranslational modifications of enzyme protein. On the other hand, exogenous H₂O₂ raised H₂S content in root tissues independently from the desulfhydrase activity. Although treatment of control plants with H₂S significantly stimulated NADPH oxidase activity and gene expression, H₂S did not affect H₂O₂ accumulation in roots exposed to Cd. The results suggest the existence of two pathways of H₂S generation in Cd‐stressed cucumber roots. One involves desulfhydrase activity, as was previously demonstrated in different plant species. The other, the desulfhydrase‐independent pathway induced by H₂O₂/NADPH oxidase, may protect V‐ATPase from inhibition by Cd.
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