Relationship between Sugars and Phenylpropanoids in Tubers from Diverse Genotypes

Previous studies suggested sucrose may play a regulatory role in potato phenylpropanoid metabolism via activation of MYB transcription factors, but the interaction between sucrose and phenylpropanoids has not been studied in field grown potatoes. Exogenous sucrose increased phenylpropanoids in plantlets, whereas wounding of tuber samples increased sucrose and phenylpropanoids. Tuber sugars and phenylpropanoids were measured in over 100 different potato samples representing different genotypes, developmental stages and locations. Total phenolic content ranged from 1.6 to 17.0 mg/g dry wt and sucrose concentrations ranged from 4.7 to 132 mg/g dry wt. Sucrose was the most abundant sugar, followed by glucose and fructose. Overall, a modest positive correlation was seen between sucrose and phenolic concentrations (R2 = 0.55; p < 0.01). Typically, tubers with a higher concentration of sucrose contained higher phenolic levels. When the same cultivars were grown in multiple locations, the tubers with the lowest amount of phenolics also had the lowest amount of sucrose. The higher amounts of phenolics found in immature potatoes relative to mature potatoes also correlated with higher amounts of sucrose. Tubers infected with Zebra chip disease had higher amounts of phenylpropanoids, and also higher amounts of sucrose. These data support a regulatory role for sucrose in tuber phenylpropanoid metabolism and suggest that the absolute amount of tuber sucrose is important, but also changes in tuber sucrose homeostasis.