Comparative carbohydrate metabolism in the shoots of a cold-hardy and a cold-sensitive peach ( Prunus persica ) cultivar during cold acclimation and deacclimation

Carbohydrate metabolism affects cold hardiness in overwintering deciduous fruit trees. In this study, we compared the changes in starch and soluble sugar contents, related enzyme activity, and gene expression in the shoots of ‘Soomee’ (SM) and ‘Odoroki’ (OD) peach ( Prunus persica ) trees during cold acclimation (CA) and deacclimation (DA). SM was cold-hardier than OD from December to March based on the LT 50 value, the temperature at which 50% injury occurred. During this period, starch contents were significantly lower in SM than in OD, along with higher total amylase activity and related gene expression. In contrast, total soluble sugar contents were significantly higher in SM than in OD, exhibiting a close relationship to cold hardiness. Of the detected soluble sugars, sucrose was predominant and its content was most significantly correlated with cold hardiness. Sucrose contents were significantly higher in SM than in OD from December to March. Fructose and glucose contents in SM, but not in OD, increased during CA and then decreased during DA concurrently with increased acid invertase activity and related gene expression. Raffinose and stachyose were detectable only from November to April. Their contents and related synthase gene expression were also significantly correlated with cold hardiness, but were not significantly different between the two cultivars. During CA, the activities of the enzymes involved in the synthesis of sucrose, raffinose, and stachyose increased with the up-regulation of their related gene expression. During DA, in contrast, the activities of the enzymes involved in the degradation of starch, sucrose, raffinose, and stachyose increased with the up-regulation of their related gene expression. Furthermore, the differential cold hardiness in the shoots of different peach cultivars was associated with the difference in enzyme activities and gene expression, especially of acid invertase, regulating soluble sugar content during CA and DA.