Abstract
Moisture content is the key factor that affects the freezing preservation of seeds. Previous studies have indicated that hydrolysis of seed storage globulins can enhance the freezing tolerance of hydrated seeds. Seed globulins are constituted by two subunits connected via disulfide bonds(-S-S-). As a donor for H2S, NaHS can act as a nucleophile to attack the disulfide bond of proteins and promote S-persulfidation. In this study, hydrated brassica (Brassica oleracea) seeds were treated with NaHS (5 mM) to confirm the role of the reduction the disulfide bonds of seed globulins on the freezing tolerance of hydrated seeds. The results indicated that NaHS treatment increased seed viability after slow cooling (NaHS vs. control: 55% vs. 38.3%) (P<0.05). Differential scanning calorimetry confirmed that supercooling occurred in embryos after NaHS treatment. NaHS treatment significantly increased the content of sulfhydryl groups in seed storage globulin, suggesting that NaHS promoted the reduction of disulfide bonds during slow cooling. Two-dimensional electrophoresis showed that NaHS promoted the depolymerization of seed storage globulins and accumulation of small polypeptides under slow cooling treatment. NaHS treatment also enhanced the levels of ascorbate and glutathione, which together make up an important antioxidant defense system against oxidative damage.