Fate of photosynthates from spur leaves of 'Nijisseiki' pear during the period of rapid fruit growth

Spurs of 'Nijisseiki' pear (Pyrus pyriflora Nakai) were allowed to assimila te (CO2)-C-13 at 87 d after anthesis (DAA) and at 108 DAA during the period of rapid fruit growth. Then the spurs were sampled periodically until frui t harvest time to trace the time course and amount of movement of assimilat es from spur leaves to individual organs in the spur. The amount of C-13 ab sorbed by fruit within 3 d after labelling was constant until harvest, rega rdless of the labelling date. However, the total amount of C-13 in the spur decreased continually until harvest. Of the total amount of C-13 recovered in the spur labelled at 87 DAA, by harvest, 43.2% of C-13 was found in the fruit flesh (cortex of receptacle), 5% in the core (pith of receptacle + p ericarp + seeds), 5.6% in spur stem, 5.4% in the source leaves, and 40.8% w as respired and exported from the spur. Of total amount of initial C-13 lab elled at 108 DAA, at harvest, the proportion of C-13 translocated to flesh, core, stem, respired, and remaining in leaves was 61%, 6.1%, 3.0%, 24% and 5.4%, respectively. Photosynthates fixed by the spur early in the rapid gr owth stage of the fruit contribute more to the formation of starch and stru ctural materials and less to soluble carbohydrates in fruit than do those f ixed later.