The ability of low and high temperatures and S-containing compounds to overcome endo- and paradormancy along with the possible mechanisms involved in these treatments for breaking `Anna' apple bud dormancy were studied. All three treatments induced budbreak in paradormant (July) and endodormant (October) buds. Cold, heat, and allyl disulfide increased ascorbic acid, the reduced form of glutathione (GSH), total glutathione, total nonprotein thiol (NPSH), and nonglutathione thiol (RSH), whereas dehydroascorbic acid and oxidized glutathione (GSSG) decreased. The treatments also increased the ratios of ascorbic acid: dehydroascorbate and GSH: GSSG and the activities of ascorbate free-radical reductase (AFR, EC 220.127.116.11), ascorbate peroxidase (EC 18.104.22.168), dehydroascorbate reductase (DHAR, EC 22.214.171.124), ascorbate oxidase (AAO, EC 126.96.36.199), and glutathione reductase (GR, EC 188.8.131.52) in the buds. These results indicate that budbreak induced by cold, heat, and allyl disulfide is associated with the removal of free radicals through activated peroxide-scavenging systems.
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