Studies on the translocation of 14C-labelled photosynthates, (1)

In order to study the translocation of photosynthates during shoot elongation, 14CO2 was fed photosynthetically to new shoots of seedlings of Abies sachalinensis Masters during the following three phases of shoot elongation: phase I (immediately after bud opening, May 31), phase II (end of shoot elongation, June 16), and phase III (matured shoots, July 19). One of these seedlings was harvested after 72 hours. In another experiment, all parts of seedlings were exposed to 14CO2, before bud opening. In the case of 14CO2 exposure to new shoots only, almost all 14CO2 photosynthates were distributed in new shoots in phases I and II. Little translocation to non-photosynthetic organs (stem, branch and root) from new shoots was noticed in these periods. In phase III, 14C activity in non-photosynthetic organs was recorded in 35.5% of all seedlings, and this value was higher than in phases I and II. When 14CO2 was exposed to all parts of seedlings before bud opening, most of 14CO2 photosynthates were translocated to new shoots. From these results, it is apparent that new shoots are a strong sink during shoot elongation and that non-photosynthetic organs are a sink at the end of shoot elongation. (auth.)