Diurnal Changes in Fixation, Transport, and Allocation of Carbon in the Sweet Potato Using 11C Tracer

Abstract

Abstract Fully expanded apical leaves of Ipomoea batatas (L.) Lam. cv. Jewel were exposed three times during the day to a square wave of 11CO2 for sufficient duration to approach steady-state isotope equilibrium in the plant. This procedure allowed monitoring of changes in the storage of photosynthate within the treated leaf and the transport and allocation of this carbon throughout the plant during the day. Early in the day, export of photosynthate from the treated leaf predominated over storage (57:43%). By mid-day, export had declined to a point that storage was favored (44:56%). Toward late afternoon, export again increased (54:46%). These changes in the allocation of carbon within the leaf were reflected by alterations in the size and turn-over time of the export pool of photosynthates within the labeled leaf. The latter increased progressively from early morning (19 min) until late afternoon (27 min). The speed of photosynthate transport within the plant varied with position along the main stem. Speeds up to 6 cm·min−1 were found between short segments of the stem (i.e. ≈10 cm). As the distance between sites increased, slow and fast rates were averaged, giving mean speeds of 2.0 to 2.5 cm·min−1. The speed of transport also changed during the day and depended, in part, on the position of the transport path along the main stem. Virtually no carbon was translocated acropetally from labeled fully expanded apical leaves during the day. Although some photosynthate was translocated into lateral branches developing at the base of the plant, the predominate sink was the root system.