Photosynthesis and distribution of photosynthates in apple shoots treated by pinching and bark ringing

Individual leaves on apple shoots treated by pinching and/or ringing were supplied with14CC2 and the rate of photosynthesis and the pattern of photosynthate distribution was studied. The ringing of the shoots as well as the ringing and pinching done together reduces the rate of photosynthesis almost by half. Pinching itself had no effect on the rate of photosynthesis. Removing the main sink — the growing shoot apex — by pinching leads to the accumulation of photosynthates in the shoot, mainly in the first internode below the pinching point. Accumulated assimilates were soon used up by the axillary meristems which were stimulated to grow by pinching. Very small amounts of assimilates (about 1 %) were translocated to adjacent shoots which were supplied by their own leaves. When adjacent shoots were defoliated, more assimilates were translocated there (nearly 8%), however, a strong tendency to accumulate the assimilates in the internode below the pinching point was observed. Assimilates are not located in matured leaves. The presence of an active sink located near the donor stimulates the mobilization of assimilates present in the donor leaf.