.Reducing sugar content was significantly greater in CA stage than in NA stage in all graft combinations (Figure 2(b)). Reducing sugar content was higher in either sweet cherry cultivars grafted on Gisela 5 rootstock compared with Mazzard rootstock in CA stages. The highest and the lowest reducing sugar contents contain in CA stage were detected in Gisela 5/Lambert (~14.0mg/g FW) and Mazzard/0900 (~9.0mg/g FW) combinations, respectively. Similar to TSS content in NA stages, no significant difference was detected in reducing sugar content of the graft combinations in NA stages. Two-way ANOVA revealed a significant effect of sampling stage, grafting combination, and the interaction of sampling stage and grafting combination on reducing sugar content (Table 1).

All graft combinations had significantly higher sucrose contents when sampled at CA than at NA stage (Figure 2(c)). When data from CA period were considered, the highest sucrose content was observed in Mazzard/Lambert combination (~9.7mg/g FW) and the lowest Gisela 5/Lambert (~7.6mg/g FW). As with TSS and reducing sugars, there were no significant differences among graft combinations in sucrose content in NA period. Two-way ANOVA revealed a significant effect of sampling stage, grafting combination, and the interaction of sampling stage and grafting combination on sucrose content (Table 1).3.3. Sucrose-Metabolizing EnzymesAcid invertase activity of all graft combinations indicated significant differences between CA and NA stages (Figure 3(a)). Acid invertase enzyme activity was significantly greater in NA stage than in CA stage in all graft combinations.

The highest and the lowest enzyme activity in CA stage were detected in Mazzard/0900 and in either sweet cherry cultivars grafted on Gisela 5 rootstocks, respectively. The highest acid invertase activity in NA stage was detected in Mazzard/0900 (0.56mg/gprot./h) while the lowest activity was detected in Mazzard/Lambert combination (0.25mg/gprot./h). Two-way ANOVA revealed a significant effect of sampling stage, grafting combination, and the interaction of sampling stage and grafting combination on acid invertase activity (Table 1).Figure 3Acid invertase (a) and SS (b) activities in cold-acclimated (CA, in January) and nonacclimated (NA, in July) bark tissues of sweet cherry cultivars grafted on different rootstock. Error bars represent �� SE of three replications.

SS activity of all graft combinations was significantly higher in NA stage compared with those in CA stage (Figure 3(b)). In addition, SS activity varied among graft combinations in both CA and NA stages. When data from the CA period were considered, the highest Batimastat SS activity was measured in Mazzard/Lambert combination (0.13mg/gprot./min) and the lowest in Gisela 5/0900 (0.04mg/gprot./min).