H₂S signal enhances storage globulin hydrolysis, embryo supercooling and freezing tolerance of hydrated brassica (<i>Brassica oleracea</i>) seeds

BACKGROUND: Seed storage globulins have two subunits linked by disulfide bonds. Earlier studies suggested that globulin hydrolysis may enhance the freezing tolerance of hydrated seeds. As a donor for H 2 S, NaHS can act as a nucleophile to break the disulfide bond of proteins and convert sulfhydryl group (‐SH) of cysteine to the persulfide group (‐SSH), which will promote formation of S-persulfidation and de-polymerization of seed globulins. OBJECTIVE: To examine the role of the H 2 S signal pathway in the freezing tolerance of hydrated brassica seeds. MATERIALS AND METHODS: Hydrated brassica (Brassica oleracea) seeds were treated with 5 mM NaHS to reduce the disulfide bonds of seed globulins and its effect on seed freezing tolerance was investigated. RESULTS: NaHS treatment increased embryo supercooling as determined by differential scanning calorimetry (DSC) and seed survival upon slow cooling (control vs NaHS, 30.0% vs 45.3%). NaHS treatment resulted in a significant increase of sulfhydryl groups of storage globulin, indicating the reduction of disulfide bonds. The 2D electrophoresis showed the depolymerization of storage globulins and the accumulation of small polypeptides. In addition, NaHS treatment increased the contents of ascorbate and glutathione for anti-oxidation. CONCLUSION: The H 2 S signal pathway is likely involved in the freezing tolerance of hydrated brassica seeds via the de-polymerization and hydrolysis of seed storage glubins, as well as the regulation of supercooling.