Root flooding of muskmelon (Cucumis melo L.) affects fruit sugar concentration but not leaf carbon exchange rate

Flooding the roots of greenhouse-grown muskmelon (Cucumis melo L. cv. Noy Yizreel) plants for 4 days reduced sucrose accumulation 36% in the inner mesocarp and 88% in the outer mesocarp of developing fruit. Concentration of the translocated sugars raffinose and stachyose were also lower in fruit on flooded plants than in those from nonflooded plants. In contrast, fruit hexose concentration was similar in both flooded and nonflooded plants. There was no alteration in activities of enzymes associated with sucrose metabolism in the fruit which could explain the decreased sucrose concentration. Four days of root flooding caused no reduction in leaf carbon exchange rate or assimilate export rate, indicating that the reduction in fruit sucrose accumulation was not due to source limitation. Root respiration, measured as CO₂ evolution, was approximately 30% lower in anaerobic roots than in aerobic roots. When viewed as carbohydrate consumed, a doubling of glycolytic activity occurred in the anaerobic root mass. Increased demand for carbohydrates by anaerobic roots may lead to a reduction in translocated carbohydrates available for sucrose biosynthesis in the developing fruit.