Sugar metabolism and accumulation in the fruit of transgenic apple trees with decreased sorbitol synthesis

Apple fruit: The advantages of a flexible sugar cycle Analysis of the sugar metabolism and transport system in apple trees shows how the fruit fructose level and fruit production is largely maintained in response to decreased sorbitol synthesis in leaves. Disruption to developmental processes and environmental factors can alter the supply of sugars from leaves to fruit. Lailiang Cheng at Cornell University, New York, US, and co-workers examined sugar metabolism and transport in modified apple trees to ascertain how a deficiency in one sugar, sorbitol, influences fruit development and sugar accumulation. Ordinarily, fructose—the sugar that generates sweeter fruit—is mainly derived from sorbitol. The modified trees compensated for sorbitol loss by increasing their sucrose supply and converting the excess sucrose into fructose and glucose, largely sustaining fruit production and fructose level. The team’s results demonstrate the metabolic flexibility of the sugar cycle in fleshy fruits