The evaluation of carbohydrate, phenol compounds changes and anti-oxidant enzymes activity during the release of dormancy in Persian walnut lateral buds by different chilling treatments

The purpose of this study was assessing the impacts of different chilling periods on the release of dormancy in walnut lateral buds, carbohydrates metabolism, phenol compounds content, and activities of soluble and cell wall peroxidase and polyphenol oxidase. In this line, one-year-old shoots were collected randomly from ten-year-old trees of Ziyarat village (Gorgan) in defoliation which were then cut into 9 cm pieces each with a single lateral bud and were subjected to different chilling treatments (0, 700, 1400 hour) at 4±1 °C and then forcing condition (25 ± 2 ◦C, 12 h light:12 h dark photoperiod, 20 µmol m−2 s−1). Results showed that 700 and 1400 chilling hours significantly increased percentage and rate of walnut lateral bud dormancy release and decreased time of initiation bud break in comparison with control. Chilling caused starch and non-reducing sugar degradation and resulted in the increase of reducing sugars. This had a positive significant relationship with the percentage of bud dormancy release. Phenols content, soluble and cell wall peroxidase activities increased up to 700 hour chilling while polyphenol oxidase activity increased up to 1400 hour as compared with control. It seems that the buildup of reducing sugars provides the required energy for dormancy release, and the increase of phenols and soluble and cell wall peroxidase activities result in decrease of oxidative stress and development of cold tolerance in buds. Moreover, rising polyphenol oxidase activity caused removing phenolic inhibitors and/or synthesis of antioxidant phenols. These processes in parallel promoted dormancy release of Persian walnut lateral buds.